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Department of Pure and Applied Chemistry Synthesis of a Novel Palladium Catalyst System and its Application in the Heck Reaction By Callum Maxwell

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Page 1: Thesis Submission

Department of Pure and Applied Chemistry

Synthesis of a Novel Palladium Catalyst System and its Application in the Heck Reaction

By

Callum Maxwell

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Acknowledgements

Firstly, I would like to thank Prof. Billy Kerr and Dr. Siddharth Patwardhan for

allowing me to undertake such an interesting and challenging project and for

advising me throughout its progress. I would also like to thank Dr. Laura

Paterson for her help throughout the duration of this project.

My special thanks to Malcolm Gordon and Rachael Dunn, for all their efforts and

for the enthusiasm and attitude they brought to the lab every day, as well as the

patience and guidance they offered.

Finally I would like to thank the rest of the Kerr Group - Calum, Natalie, Laura

“Goldie”, Marc, Murali, Richard, Andy, and my fellow undergraduates, Tim and

Amelia, for all their help throughout my time in the lab.

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Contents

Acknowledgements ....................................................................................................... 2

Contents......................................................................................................................... 3

List of abbreviations ...................................................................................................... 6

1. Abstract...................................................................................................................... 7

2. Aims and objectives .................................................................................................. 8

3. Introduction ............................................................................................................. 10

3.1 Cross-coupling reactions .......................................................................................................................10

3.1.1 Palladium-catalyzed cross-coupling ..........................................................................................10

3.2 Heck Reaction .............................................................................................................................................12

3.2.1 Mechanism ...........................................................................................................................................12

3.2.2 Regioselectivity...................................................................................................................................14

3.3 Homogeneous catalysis ..........................................................................................................................15

3.4 Heterogeneous catalysis ........................................................................................................................16

3.5 Nanoparticle catalysis .............................................................................................................................17

3.6 Formation of silica ....................................................................................................................................18

3.5 Biosilification ..............................................................................................................................................20

3.5.1 Controlling effects on porosity and surface area ..................................................................20

3.5.2 Alternative supports .........................................................................................................................22

3.6 Analysis of heterogeneous catalysts .................................................................................................23

3.6.1 Thermogravimetric analysis .........................................................................................................23

3.6.2 Transmission electronic microscopy ..........................................................................................24

3.6.2 BET analysis.........................................................................................................................................25

3.6.3 BJH analysis .........................................................................................................................................28

4.Previous work ........................................................................................................... 29

5. Results and discussion............................................................................................. 34

5.1 Objectives .....................................................................................................................................................34

5.1.1 Synthesis of the silica support.......................................................................................................35

5.1.2 Preparation of palladium nanoparticles on silica ................................................................37

5.1.3 Synthesis of palladium catalysts ..................................................................................................38

5.1.3 Calcination ...........................................................................................................................................40

5.2 Investigating the physical properties of the catalyst.................................................................41

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5.2.1 BET testing ...........................................................................................................................................42

5.2.3 ICP testing.............................................................................................................................................43

5.2.4 BJH analysis .........................................................................................................................................46

5.2.5 Conclusions ..............................................................................................................................................47

5.3 Catalyst Testing..........................................................................................................................................48

5.3.1 Objectives..................................................................................................................................................48

5.3.2 Test of uncalcinated catalyst ........................................................................................................52

5.3.3 Test of calcinated catalyst..............................................................................................................53

5.3.3 Substrate scope...................................................................................................................................54

5.3.4 Electronic effects on the Heck reaction.....................................................................................55

5.3.5 Steric effects on the Heck reaction..............................................................................................57

5.3.6 Investigation into the effects of catalyst loading ..................................................................58

5.4 Conclusions ..................................................................................................................................................60

6. Future work ............................................................................................................. 61

7. Experimental............................................................................................................ 62

7.1 General ...........................................................................................................................................................62

7.2 General Procedures ..................................................................................................................................62

7.2.1 General Procedure A: Preparation of silica catalyst support ...........................................62

7.2.2 General Procedure B: Preparation of catalyst .......................................................................63

7.2.3 General Procedure C: Calcination of the prepared catalyst ..............................................64

7.2.3 General Procedure D: Standard Reaction for testing ..........................................................64

7.2.4 General Procedure E: Standard Reaction with additive PPh3 ..........................................64

7.3 Synthesis of silica support.....................................................................................................................65

7.4 Synthesis of palladium catalyst...........................................................................................................66

7.5 Calcination of prepared catalyst .........................................................................................................67

7.6 Determination of standard reaction conditions ..........................................................................68

7.6.1 Synthesis of methyl 3-(4-acetylphenyl)acrylate ....................................................................68

7.7 Testing of uncalcinated catalyst .........................................................................................................70

7.7.1 Synthesis of methyl 3-(4-acetylphenyl)acrylate ....................................................................70

7.8 Test of Calcinated catalyst.....................................................................................................................71

7.8.1 Synthesis of methyl 3-(4-acetylphenyl)acrylate ....................................................................71

7.9 Investigation into the effects of electronics on the Heck reaction.......................................72

7.9.1 Synthesis of methyl 3-(4-(trifluoromethyl)phenyl)acrylate .............................................72

7.9.2 Synthesis of methyl 3-(4-acetylphenyl)acrylate ....................................................................73

7.9.3 Synthesis of methyl 3-(p-tolyl)acrylate .....................................................................................74

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7.9.4 Synthesis of methyl 3-(4-acetylphenyl)acrylate ....................................................................74

7.9.5 Investigation into the effect of steric hindrance on the Heck reaction ..........................76

7.10 Investigation into the effects of catalyst loading ......................................................................76

7.10.1 Synthesis of methyl 3-(4-(trifluoromethyl)phenyl)acrylate ...........................................76

8. Appendix 1 ............................................................................................................... 78

8.1 Calculating the molar loading of the catalyst ................................................................................78

8.2 Calculating loading of the catalyst (% w/w) .................................................................................81

9. Appendix 2 ............................................................................................................... 83

10. Bibliography........................................................................................................... 86

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List of Abbreviations

amu Atomic mass units

BET Brunauer-Emmett-Teller

BJH Barrett-Joyner-Halenda

[bmim][BF4] 1-Butyl-3-methylimidazolium

tetrafluoroborate

cm Centimetres

DCM Dichloromethane

DMF Dimethylformamide

DMSO Dimethyl sulfoxide

Et3N Triethylamine

h Hours

ICP-MS Inductive coupled plasma - Mass

Spectroscopy

J Coupling Constant

m Metres

MHz Megaherts

min Minutes

mg Milligrams

ml Millilitres

mmol Millimol

Pd(OAc)2 Palladium Acetate

PEHA Pentaethylenehexamine

PVP Polyvinylpyrrolidone

S.M. Sodium metasilicate

TGA Thermogravimetric Analysis

TEM Transmission Electronic Microscopy

TEOS Tetraethyl orthosilicate

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1. Abstract

The following work details a method developed for the bioinspired preparation

of a palladium catalyst and the preliminary investigations into its use in metal

heterogeneous catalysis.

Inspired by biosilification and replicated in the laboratory, silica aggregations

were prepared using pentaethylenehexamine (PEHA) in aqueous solution. The

method used was extended to incorporate palladium nanoparticles onto the

silica prepared creating a low energy, low cost preparation of a heterogeneous

palladium catalyst.

The preliminary investigations into the stability and activity of the catalyst have

focused on the cross-coupling Mizoroki-Heck reaction between methyl acrylate

and a range of aryl halides.

The range of aryl halides available were used to investigate how the electronic

effect experienced by the halide affected the overall efficiency of the catalyst in

the system.

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2. Aims and Objectives

In the present economic climate, energy costs are rising, fossil fuels are running

out and the impact is being felt across all industries. Recently in America, Forbes

reported on a major movement indicating that it is time for universities to divest

their investments in fossil fuels.[1] This is a major sign that the environmental

and moral costs of fossil fuels are catching up with the economic value associated

with them. As a result of the rising cost of energy from fossil fuels it is of

paramount importance to find low energy methods to prepare effective catalysts

that are active and cheap to produce.

Taking inspiration from biology, where plants and grasses are able to synthesise

silica naturally to strengthen their cell walls, bioinspired silica has been

produced whilst replicating the mild conditions associated with its natural

synthesis.[2] The green routes associated with biosilification represent an

opportunity to reduce the cost, both economically and environmentally, of

nanoparticle catalysis.

The applications of bioinspired silica are numerous, however this project will

focus on the use of the silica as a system for catalyst support. With this in mind,

gaining an understanding of the overall process, and synthesising a silica support

using a bioinspired method under mild conditions was the first aim of the

project.

In this project, pentaethylenehexamine (PEHA) was used in the preparation of

the modified-silica due to its ability to control the particle size of the silica and

the physical properties of the overall support prepared, such as the surface area

and pore size.

The second aim of this project was to prepare a palladium catalyst by

incorporating palladium nanoparticles into the bioinspired silica during its

preparation. The novel approach to the preparation of this catalyst aimed to be

environmentally friendly with little chemical waste and a low energy cost. By

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preparing the catalyst at room temperature, with mild pH, and using water as a

main solvent, it was hoped that this low cost preparation could be scaled up as a

method to produce highly active and alternative catalyst systems for cross-

coupling reactions at a far reduced cost.

Since the morphology of the silica prepared was controllable, this project aimed

to prove the robustness of the reaction by keeping the physical properties of the

silica supports consistent during separate catalyst preparations. To investigate

the physical properties of the catalyst prepared Brunauer-Emmett-Teller (BET)

and Barrett-Joyner-Halenda (BJH) analysis were both used, as they would allow

the surface area and specific pore size of the catalyst to be examined.

To investigate the activity and versatility of the catalyst system prepared, the

Heck reaction was identified as a suitable reaction candidate. By using a range of

substrates the transformational capabilities of this catalyst system were hoped

to be identified, as well as where its limitations appear.

Currently heterogeneous catalysts do not have a particularly high turnover

number, and poor reusability is a trait common due to leaching of the catalyst

from its support into the respective reaction mixtures. The final objective of the

project was therefore to investigate the reusability of the catalyst. If the catalysts

prepared using the green route are as recyclable as the current catalyst systems

available, they will represent a significant drop in cost.

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3. Introduction

3.1 Cross-coupling reactions

Cross-coupling reactions are some of the most important reactions used in

chemistry today. The cross coupling reaction has the sole aim of generating a

new carbon to carbon bond, and palladium is the most widely chosen metal to

act as the catalyst for the reactions.[3] Scheme 1 shows the general form of a

cross coupling reaction; R1 is an organic fragment of a molecule, X is a good

halide or triflate, and R2 is a different organic fragment, usually attatched to a

metal species. In the presence of a metal catalyst and a base, the reaction will

bond the two organic fragments.

Scheme 1

3.1.1 Palladium-catalyzed cross-coupling

Palladium has been utilised as a catalyst in many different cross-coupling

reactions, for example, the Suzuki-Miyaura reaction, Hiyama-coupling, Negishi

coupling and the Heck reaction.

The Suzuki-Miyaura reaction (Scheme 2) was first published in 1979 and

involves the coupling of an aryl or vinyl borane with an aryl or vinyl halide or

pseudo-halide (e.g. triflate).[4],[5] Palladium (0) is used to catalyse the reaction,

with the desired product being obtained in an excellent 98% yield.

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Scheme 2

Scheme 3 shows the Hiyama-coupling, first discovered in 1988, which is a cross

coupling reaction of an organosilane with an organohalide or triflate in the

presence of a fluoride source.[6],[7] Scheme 3 indicates that the Hiyama-coupling

can be carried out at room temperature.

Scheme 3

The Negishi-coupling was first published in 1977 and involves the coupling of an

organozinc compound with an organic halide or triflate.[8] The reaction is

commonly carried out using either palladium or nickel as the catalyst (Scheme

4).[9] In the case of the Negishi coupling, the metal incorporated into the second

organic fragment is Zinc. Similarly with the Hiyama-coupling, the Negishi-

coupling can be carried out at room temperature.

Scheme 4

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3.2 Heck Reaction

The Heck reaction was first reported in the late 1960’s and involves the reaction

between an unsaturated organohalide and an olefin, to produce a new

unsaturated product as illustrated in Scheme 5.[10],[11],[12]

Scheme 5

3.2.1 Mechanism

The general mechanism for the Heck reaction and the catalytic cycle can be seen

in Scheme 6. When the reaction is carried out under a palladium (II) source, it is

first reduced from Pd(II) to Pd(0) to allow the palladium to initiate the catalytic

cycle. Such reduction of Pd (II) to Pd (0), can be carried out using, for example,

PPh3. The first step of the catalytic cycle is oxidative addition, in which palladium

inserts into the carbon – halide bond which results in the palladium (II) species.

Following oxidative addition, carbometallation occurs which involves the

insertion of the olefin into the carbon-palladium bond. β-hydride elimination

then occurs to produce the product, before the palladium (0) is reformed via

reductive elimination.[12] The catalytic cycle is completed at this stage and, as

shown in Scheme 6, the reformation of palladium (0) allows the reaction to be

naturally catalytic in palladium (0). The number of catalytic cycles able to be

completed before reactants run out is known as the turnover.

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Scheme 6

The Heck coupling mechanism shown above indicates the group X is initially

connected to an unsaturated organic molecule (e.g. R=Ar). The X group, as in the

previously discussed cross-coupling reactions can be an iodide, bromide,

chloride or triflate. The alkene can be mono, di, tri or tetrasubstituted.

Within the catalytic cycle, attaching phosphine ligands can further stabilise the

palladium catalyst. Under these conditions, the palladium (0) complex will be

more stable and therefore the risk of palladium black formation, which is

catalytically inactive, will be significantly reduced. Another method to reduce the

formation of palladium black is to lower the catalyst loading. This can also

encourage ligandless systems to succeed.Error! Reference source not found.

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3.2.2 Regioselectivity

Within the Heck reaction, attaching an electron-withdrawing group to the alkene

results in the arylation or vinylation selectively occurring at the β-position of the

alkene as shown in Scheme 7.[15] Additionally, when more electron rich alkenes

are employed, a reversal in regioselectivity is observed.

Scheme 7

Where less electronically bias alkenes are used as reactants in the Heck reaction,

regioselectivity is not as pronounced, with a mixture of α- and β-substituted

alkenes forming. Following the same procedure as Scheme 7, examples of

reactants that will produce a mixture of and products are shown in Figure 1.

Figure 1

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3.3 Homogeneous Catalysis

Homogeneous catalysis refers to a catalytic system in which the catalyst and the

substrates are in the same phase in the reaction mixture. In most cases this will

be the liquid phase. Under these conditions some problems occur when

separating out the products from the reaction mixture, especially when working

with nanoparticles.

Within industry, homogenously catalyzed reactions are of a smaller significance

than most heterogeneously catalyzed reactions, since heterogeneous catalysis

creates all the raw materials and building blocks for chemicals.[16] Perhaps the

most important reaction from a homogenous standpoint is hydrogenation, such

as the hydrogenation of alkenes using Wilkinson catalyst (RhCl(PPh3)3),

(Scheme 8). The yield of product observed in the reaction was 80%.[17]

Scheme 8

The selectivity of the hydrogenation is controllable using different reactants and

alternative catalysts. In industry asymmetric hydrogenation is used in the large-

scale synthesis of the precursor to L-Dopa (Scheme 9), which is widely used in

the pharmaceutical industry. L-Dopa is then synthesised by acid catalysed

hydrolysis.[18]

Scheme 9

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3.4 Heterogeneous Catalysis

In contrast to homogeneous catalysis, heterogeneous catalysis refers to a

catalytic system in which the catalyst is in a different phase to the reaction

mixture. There has been significant research into heterogeneous catalysis, and in

particular, the concept of attaching metal nanoparticles into a solid support has

been a successful idea through recent history. Placing a catalyst, such as

palladium metal in the Heck reaction, into a stable support allows the

opportunity to create new reactive catalysts for industry.[19], [20]

Since the recovery of a heterogeneous catalyst is both easy and cheap, this serves

as main advantage over homogeneous catalysis. Reusability of catalysts is

extremely important when trying to reduce the costs of industrial scale

reactions.

The main physical properties associated with a successful catalyst are pore

volume and surface area.[21] The support chosen will differ from reaction to

reaction but the support chosen must be completely inert to the reaction

conditions it finds itself in. Three commonly used support materials used for

heterogeneous catalysis are alumina, silica, and carbon. These materials all have

high melting points as well as high decomposition temperatures. The

characteristics of the catalyst support such as pore size, surface area and pore

distribution, can be characterised for these materials using BET and BJH

analysis.[21]

The support network used can also have an effect on the reactivity of the

catalyst. As well as preventing the build up of palladium molecules congregating

and creating palladium black, chemicals such as bismuth have been shown to

improve the activity of heterogeneous catalysts in cross-coupling reactions. The

support structure shown in Figure 2 ([BiPd(O2CCF3)5(HO2CCF3)]2) gives an

indication of how complex the chemistry of the support network has become.

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Figure 2

Mesoporous silica is extremely stable both thermally, as well as chemically and

has the bonus of a relatively simple synthesis. As far as the desired

characteristics of a support go, silica is an excellent choice from a catalytic point

of view. Its high thermal and chemical stability mean that it will not change form

and increase leaching during a reaction.[22] Silica’s stability will prevent the

catalyst support decomposing under reaction conditions, and allow the catalyst

to be long living.

3.5 Nanoparticle catalysis

As previously noted (Section 3.4), generally the higher the surface area of a

catalyst the more effective it will be. Therefore, making the particles of your

catalyst as small as possible will generate the largest surface area and in turn , the

most effective catalyst. Generally, a nanoparticle is any particle between 1 and

100 nm in size.[23] As well as the ability to generate catalysts with high surface

areas, nanoparticle technology has also resulted in a few chemicals such as gold,

which is usually considered chemically inert, to be effective as a catalyst.[11],[24]

As a result of this, nanoparticles have become a major interest to the catalyst

industry. In Figure 3, the graph shown indicates the decrease in activity of gold

nanoparticles on different catalyst supports, as the diameter of the gold

nanoparticles increases.

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Figure 3

3.6 Formation of silica

Passing oxygen over the surface of elemental silicon traditionally forms Silicon

Dioxide, (silica). At high temperatures (between 600 and 1200oC) and using

either dry or wet oxidation techniques, multiple layers of silica can be formed

whilst maintaining control of the physical properties of the product. The reaction

for the wet oxidation technique is shown in Scheme 10.[25]

Scheme 10

At higher temperatures, the layer of oxide produced increases in thickness from

1 micron at 920oC to around 1.08 microns at 1200oC (Figure 4).[25]

Si 2H2O2 SiO2 2H2920 - 1200oC,

10 h.

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Figure 4

The dry oxidation technique is carried out under similar conditions although

oxidation can occur at temperatures as low as 700oC, (Scheme 11).[25]

Scheme 11

In the experiment carried out by Deal et al., at 700oC an oxide thickness of 0.05

microns was observed, whilst at 1200oC an oxide thickness of 1 micron was

recorded (Figure 5). This correlates well with the information from the wet

oxidation of silicon, where the same pattern was recorded.

Figure 5

Si O2 SiO2700 - 1200oC,

30 - 100 h

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Traditional methods of forming silica such as wet and dry oxidation require high-

energy input to produce the product. Another method of forming silica is by the

sol-gel method, which is a type chemical solution deposition.[26] The most

common reaction for the sol-gel preparation of silica involves the hydrolysis of

tetraalkoxysilanes, Si(OR)4, (Scheme 12).[27]

Scheme 12

One of the most common precursors for sol-gel preparation of silica is tetraethyl

orthosilicate (TEOS).[28],[29] To obtain nanoscale silicon dioxide powder, the

crude product is required to be calcinated in a furnace, which requires a high

energy input. This is the main disadvantage to the preparation of silica using the

sol–gel method.[30]

3.5 Biosilification

Biosilicification is the synthesis of silica in vivo, that is, in a natural environment.

For catalysis this could be a very important process used to build structural

supports for nanoparticles. The biological silica formation brings with it some

very interesting features, including the fact that it occurs at mild pH and ambient

temperatures.[31] This environmentally friendly technique is also controllable,

something sought after in synthetic synthesis. Biologically inspired silica has

seen the use of additives in an effort to try and manage the characteristics of the

silica formed. For example the pore size and surface area of the catalyst can be

controlled depending on which substrate is used in the bioinspired silica

synthesis.

3.5.1 Controlling effects on porosity and surface area

One advantage of biosilification is the ability to influence and change the pore

size of the support for a catalyst, and hence can improve the catalyst’s efficiency.

Si(OC2H5)4 H2Ocatalyst

SiO2 4C2H5OH

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As one of the most important factors affecting the efficiency of a catalyst the

ability to influence the pore size of the catalytic support is an important

advantage of biosilification. By using different substrates in the initial synthesis

of the silica, the pore size of the support, as well as the surface area, can be

tailored to suit the properties required of each individual catalyst.

The range of surface area tailored can range from <10 up to 1030 m2 g-1 with

pore sizes ranging from <2 up to 60 nm, with the advantage of having a fast

preparation and mild conditions associated with biosilification.[32-37] In contrast,

using non-bioinspired routes of synthesis such as sol-gel processing, high surface

areas and high porosity silica can be synthesised but only using methods and

commonly harsher conditions than biosilification required.[38], [39]

Coradin et al., were able to produce a silica support containing 2 distinctive pore

sizes, mesopores of diameter 2.5-3.5 nm and meso-to-micropores with a

diameter span of 10-100 nm, using surfactants derived from amino acids. The

resulting support also had a high surface area (>500 m2 g-1).[40] Conversely,

propylamines, such as the amines found in the diatom algae, have been shown to

influence the surface area of the silica precipitating to a surface area of

<10 m2 g.[41]

Through implementing biosilification into synthetic chemistry, it is possible to

replicate the mild conditions associated with the silica production. By eventually

understanding its process, biosilification could be scaled up to be used in

biotechnological processes, for example, bioimplants (the materials used from

human or animal origin to replace or support biological systems), and enzyme

immobilisation (the process of placing an enzyme onto an insoluble solid).[42], [43]

Metal oxides can also support catalysts and these have been employed in

numerous areas, for example Suzuki coupling reactions. For example, M. Kantam

et al., synthesised a catalyst using palladium nanoparticles that had been

synthesised by counter ion stabilisation of [PdCl4]2- with nanocrystalline

magnesium oxide, followed by a reduction.[44] The catalyst synthesised showed

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good reactivity for aryl bromides and aryl iodides. For a 0.5 % loading of this

catalyst, the Suzuki coupling was carried out in 6 hours at room temperature.

However, in the experimentation, the loading of the catalyst was reduced to

0.01% and was effective. The high surface area of the magnesium oxide support

(≈ 600 m2 g-1) was attributed to the activity of the catalyst.

3.5.2 Alternative Supports

Carbon nanotubes have also been used to support palladium catalysts.[45]

Alternative methods of encapsulating the palladium on the surface of the tubes

have been employed such as impregnation, [46] supercritical fluid attatchment, [47]

and pyrolysis.[48] Pyrolysis is a type of thermolysis carried out at increased

temperature without the presence of oxygen, and is one of the simplest methods

of placing the palladium onto carbon nanotubes such as in Scheme 13, where

the palladium particles become trapped within the carboxylic acid

functionality.[48]

Scheme 13

Recently, more organic materials such as functionalised polymers have been

used to support metal catalysts in coupling reactions.[49] Polymers can be

extremely versatile when used as supports, they allow for the recycling of the

catalysts, as well as the high efficiency normally associated with homogeneous

catalysts. Sayed et al. used PVP polymers as a support for palladium catalysed

method to anchor metal nanoparticles on the surface of carbon

nanotubes.24 The metal nanoparticle–nanotube heterogeneous

architectures have been employed in fuel cells,25 electrocatalytic

reactions,26 different gas sensors27 and only a few reports include

catalytic applications in Heck, Suzuki, Stille, and Sonogashira

coupling reactions.28 However, the catalytic application of

nanotube–metal nanoparticle composites in acyl Sonogashira

coupling reactions has been missing till to date. In the present

study, a simple synthetic process was adopted to anchor

palladium nanoparticles (PdNPs) onto the surface of carboxylic

acid functionalized SWNTs following our recent approach to

synthesize heterogeneous PdNPs anchored in a polymer

matrix.29 We tested the SWNT–PdNPs as a catalyst in acyl

Sonogashira reaction under copper free condition to synthesize a

library of ynones. The ‘‘ynones’’ are multipurpose isolable

intermediates in the synthesis of pharmaceutically prominent

and biologically active N-heterocyclic compounds, such as

pyrroles,30 pyrazoles,31 isoxazoles,32 pyrimidines,33 quinolines,34

and tetrahydro-b-carbolines.35 Synthetic methods for the pre-

paration of ynones utilize well defined palladium catalysts for

coupling of terminal alkynes with an acid chloride (acyl

Sonogashira reaction)29,36 or with organic halides in the presence

of carbon monoxide (carbonylative Sonogashira reaction).37 A

recent literature survey unveils that most of these studies

exploited the use of copper as a co-catalyst, which in turn makes

the separation of the products more tedious, generating alkyne

homocoupling bi-products. Nevertheless, the acyl Sonogashira

reaction remains the more straightforward process for the

generation of ynones avoiding poisonous carbon monoxide

gas, and it can also be extended to design sequential reactions in

a one-pot fashion leading to pharmaceutically important

heterocycles.29 Thus we embellish the carboxylic acid functiona-

lized SWNT’s surface with palladium nanoparticles to quench

the thirst in developing copper free recyclable palladium

catalysts for acyl Sonogashira coupling with mild reaction

conditions yielding a library of ynones with excellent yield.

Additionally, SWNT-PdNPs composite displays promising

catalytic efficiency for trimethylsilylacetylene (analogous of

terminal alkyne) furnishing derivatives of trimethylsilyl-ynones

(TM S-ynones) which are further utilized in the synthesis of 2,4-

disubstituted pyrimidines in high yields through multicomponent

and sequential one-pot processes (Scheme 1).

Results and discussion

As a part of our ongoing interest in developing palladium

nanocatalysts for different organic transformations,29,38 herein,

we utilized carboxylic acid functionalized SWNTs as templates

for anchoring palladium nanoparticles via thermolysis of

palladium acetate under inert atmosphere avoiding the use of

any external hazardous reducing agents (Scheme 2).

In the current strategy, SWNT–PdNPs nanocomposite can be

accomplished after mixing carboxylic acid functionalized

SWNTs and palladium acetate in dry DM F followed by one

hour sonication and thermal treatment at 95 uC for four hours.

The as-synthesized SWNT–PdNPs were characterized by trans-

mission electron microscopy (TEM ), energy dispersive X-ray

spectrum (EDX), scanning electron microscopy (SEM ), atomic

force microscopy (AFM ), ICP-AES, X-ray photoelectron

spectroscopy (XPS), UV-vis-NIR spectroscopy, and resonance

Raman spectroscopy.

TEM images, recorded on a carbon–copper grid following a

drop-cast method from a very dilute sample in DM F, revealed

the presence of palladium particles having nanospheric dimen-

sion (Fig. 1A,B) in between the range 5 to 14 nm (Fig. 1C) and

EDX spectrum collected from TEM confirmed the presence of

palladium in the SWNT–PdNPs sample (see ESI { ). The SEM

Scheme 1 One-pot synthesis of 2,4-disubstituted pyrimidines catalyzed

by SWNT-PdNPsusing acyl Sonogashira reaction protocol under copper

free condition.

Scheme 2 A schematic representation for thesynthesisof SWNT–PdNPs

considering a small part of the nanotube–nanoparticle architectures.

Fig. 1 (A) TEM image of SWNT–PdNPs recorded on a carbon–copper

grid; (B) magnified TEM image of SWNT–PdNPs in 10 nm scale

revealing the presence of palladium nanoparticles attached to single

walled carbon nanotubes; (C) size distribution histogram of palladium

nanoparticles decorated on single walled carbon nanotubes.

7524 | RSC Adv., 2012, 2, 7523–7533 This journal is ß The Royal Society of Chemistry 2012

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Suzuki cross coupling reactions.[50] By varying the size of the palladium

nanoparticles they were able to investigate the effect that particle size had on the

turnover frequency of the Suzuki reaction. The results they obtained showed

that as the particle size increased, the turnover frequency decreased, suggesting

that the Suzuki reaction was structure sensitive. They also observed low activity

with very small particles, which could be attributed to the poisoning effect by the

intermediates formed.

3.6 Analysis of heterogeneous catalysts

After selecting an efficient method of synthesising the catalyst it is important to

select a method to analyse its physical composition. Different techniques can be

used to investigate the physical and chemical characteristics of a catalyst.

3.6.1 Thermogravimetric Analysis

Thermogravimetric analysis (TGA) is one such method of analysis.[51] In TGA

the rate of change in the weight of a substance is plotted as a function of the

temperature, as percentage residue. The changes in mass as the temperature

increases give an indication of the composition of elements within the

material. This allows an understanding of the thermal stability and chemical

make up of a catalyst. Figure 6, from Davar et al., indicates that as

temperature increases, the weight of the structure decreases as fragments are

removed from the molecule.[52]

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Figure 6

3.6.2 Transmission Electronic Microscopy

Transmission electron microscopy (TEM) is a method of microscopy that uses a

focused beam of electrons travelling through a sample of a material to generate

an image of the material in the same way as a light microscope. When de Broglie

released his paper on the de Broglie hypothesis (the proposal that all matter

exhibits wave-like properties, as photons do),[53] a group working at the

Technological University of Berlin believed that using electrons rather than light

would allow for an image of much higher resolution to be produced.[54] This

effect is due to electrons having a much lower de Broglie wavelength than light.

In Figure 7, shown below, nanosheets of palladium metal have been

photographed using TEM, and the structure of the palladium on the sheet in

shells is clear. [55]

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Figure 7

3.6.2 BET analysis

BET analysis was based on the BET theory developed and first published in

1938.[56] Based initially on Langmuir’s theory for monolayer molecular

adsorption, BET theory is an extension of molecular adsorption to incorporate

multilayer adsorption.[57]

Irvine Langmuir, who won a Noble prize based on his work, first derived the

Langmuir adsorption model in 1916. The model is based on single-layered

adsorption and can easily be applied to catalysts. In Figure 8, the model is

shown as a gas next to a planar surface, with gas molecules being adsorbed onto

this surface.

Figure 8

CP302 Part 3 9

Type II isotherms correspond to strong adhesion at low pressure, hence the steep initial slope, and either very wide pores or an isolated surface. After the initial monolayer is formed the isotherm becomes nearly horizontal, but then begins to curve upwards again as the saturation pressure is approached. This upturn corresponds to the formation of multilayers and ultimately a layer of liquid starts to form on the surface, called a wetting layer, whose thickness is unbounded as the saturation pressure is approached. Type III isotherms are similar to type II isotherms, except gas adhesion to the surface is much weaker. Type IV isotherms are characteristic of adsorption in mesoporous materials where gas adhesion to the surface is strong. Initially, monolayer or multilayer adsorption occurs at low pressure. The hysterisis loop occurs because of capillary condensation, whereby gas condenses to liquid within the mesopores at a pressure lower than the bulk saturation pressure. Type V isotherms are similar to type IV isotherms, except that gas adhesion to the surface is weak.

3.4. Langmuir isotherm

Microporous adsorbents are usually used to separate mixtures of gases. So we will mostly be concerned with type I isotherms. It is useful to be able to represent these kinds of isotherm in terms of an adjustable function, and the Langmuir isotherm is the simplest example. Much more sophisticated modelling techniques, such as those based on �statistical mechanics� (which is the physical theory that lies behind thermodynamics), are able to reproduce all these isotherms as well as other adsorption effects. Irvine Langmuir, who received the Noble Prize for chemistry in 1932, derived his eponymous equation in 1916, as well as a simple method for fitting it to experimental data. It must have been a short paper, because we can easily re-derive both the equation and fitting method! Consider Figure 3.

S surface

sites

only F are filled

gas next to

surface with concentration C

Figure 3 � illustrating Langmuir�s model for surface adsorption

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The planar surface, shown above, has a maximum number of surface sites, S. Of

these sites, only the amount, F, are filled. Irvine Langmuir based his model on

assumptions he made which are listed below;

The surface of the adsorbing site is perfectly planar,

the gas is stationary when adsorbed onto the surface,

all sites are equivalent,

one molecule can only be adsorbed to one site at a time,

there are no interactions between adjacent sites.

From these assumptions Langmuir derived an equation to calculate the

fractional coverage of the surface by the gas (Equation 1) where 𝜃 is the

fractional coverage of the surface, 𝛼 is the Langmuir constant, which varies

depending on the substrate, and P is the gas pressure or concentration.

𝜃 = 𝛼 .𝑃

1 + 𝛼 .𝑃

Equation 1

BET theory uses the same assumptions as Langmuir theory, but it also includes

three more to address some problems with Langmuir theory. The first is that gas

molecules will physically adsorb on a solid in layers infinitely, the second

assumes the different adsorption layers do not interact and the third assumes

that the theory can be applied to each layer.[58] Equation 2 is the accepted form

of the BET equation, where vm is the monolayer absorbed gas volume, v is the

measured volume of gas adsorbed, x is equal to 𝑝

𝑝0 and c is the BET constant.

𝑣 =𝑣𝑚. 𝑐. 𝑥

(1 − 𝑥)(1 − 𝑥 + 𝑐𝑥)

Equation 2

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Rearranging Equation 2 gives the graphical representation of the BET isotherm,

Equation 3;

𝑥

𝑣(1 − 𝑥)=

1

𝑣𝑚𝑐+

𝑥(𝑐 − 1)

𝑣𝑚𝑐

Equation 3

From the values obtained for 𝑥

𝑣.(1−𝑥) and from experimental data, a graph can be

plotted with 𝑝0

𝑝 on the x-axis to create a BET plot. The gradient of the slope of the

linear line is used to calculate the monolayer adsorbed gas quantity (vm) as

shown in Equation 4, where A is the slope of the BET curve and I is the y-

intercept;

𝑣𝑚 = 1

𝐴 + 𝐼

Equation 4

vm is then used to calculate the total surface area in Equation 5, where SBET,total is

equal to the total surface area, N is Avogadro’s number, s is the cross section for

adsorption and V is molar volume of adsorbate gas;

𝑆𝐵𝐸𝑇 ,𝑡𝑜𝑡𝑎𝑙 =(𝑣𝑚𝑁𝑠)

𝑉

Equation 5

From total surface area of material the specific surface area, SBET and 𝑎 is equal to

the mass of adsorbent;

𝑆𝐵𝐸𝑇 =𝑆𝐵𝐸𝑇 ,𝑡𝑜𝑡𝑎𝑙

𝑎

Equation 6

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3.6.3 BJH Analysis

Another method of analysing the physical characteristics of catalysts is the

Barrett-Joyner-Halenda (BJH) analysis, which is used to calculate pore area and

specific pore volume. This method of analysis uses a modification to the Kelvin

equation to incorporate condensation occurring with in the pores of a

material.[59] The Kelvin equation is used to calculate pore size distribution and is

shown in equation 7, where d is pore size distribution, p is vapour pressure, p0

is the saturated vapour pressure and the surface tension is .

𝑑 =2. 𝛾.𝑉𝐿

𝑅𝑇𝑙𝑛(𝑝0𝑝 )

Equation 7

The modified form of the Kelvin equation incorporates the thickness of the

multilayers of condensation occurring in the pore walls, t, (Equation 8).

𝑑 =2. 𝛾. 𝑉𝐿

𝑅𝑇𝑙𝑛(𝑝0𝑝 )

+ 2𝑡

Equation 8

Having stated all of the above, it is clear that there are many different catalytic

systems widely in use. As energy supplies appear to dwindle, the interest in

synthesising efficient catalysts and their subsequent systems increases. Although

the number of systems is numerous, the investment into research continues. The

latest breakthroughs in the chemistry of catalysts are likely to come from our

ability to replicate nature, reducing the cost of building highly efficient catalyst

systems. With this in mind, this project will attempt to use the process of bio-

inspired silica as a support for palladium, in the hope of proving that catalysts

synthesised this way can be efficient and cost efficient. The Heck reaction will be

used as a means to test the effectiveness of the catalyst, while BET and BJH

testing will be used to investigate the physical properties of the catalyst.

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4.Previous work

Previously within the University, Javier Barral undertook a project that aimed to

investigate the use of bioinspired synthesis of silica as a catalyst support. A

reaction system was identified to prepare the silica produced on a consistent

scale with consistent properties.[60]

The reaction system for the preparation of the silica was adapted as a support

system for a catalyst, and accordingly, palladium nanoparticles were

incorporated into its structure. Each batch of catalyst was prepared and analysis

of physical properties using BET and ICP analysis were carried out to determine

the loading of the catalyst. BJH analysis was also used to investigate the pore

area and specific pore volume of the catalyst support. Table 2 shows the results

obtained during physical characterisation of the silica prepared. In this case the

results reflect the characteristics of a catalyst on a 9.3 and 7.0 mmol scale

(sodium metasilicate).

Entry Scale S.M. (mmol)

BET surface area (m2/g)

Pore Volume (cm3/g)

BJH adsorption: Average Pore

Diameter (4V/A) /nm

BJH desorption: Average Pore

Diameter (4V/A) /nm

1 9.3 20.772 0.03803 14.1127 10.4392

2 7.0 20.397 0.05707 12.8096 12.4274

Table 2

From Table 2 it is clear that the previous work carried out obtained silica with

very consistent physical conditions. Although there was some variance between

the scale of Entry 1 and 2, the BET surface area for both entries varied only

slightly (20.772 m2/g and 20.397 m2/g). This trend continued across pore

volume associated with each entry (0.03803 cm3/g and 0.05707 cm3/g). There

was a larger difference between BJH adsorption pore diameters, with Entry 1

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having a pore diameter of 14.1127 nm compared to 12.8096 nm in Entry 2. This

difference is continued in BJH desorption pore diameter, where the Entry 1 has a

pore diameter of 10.4392 nm whilst Entry 2 was ≈ 2 nm larger. No comment was

made on the reasons for these minor differences, however it may have been

down to experimental error.

Having investigated the physical properties of the catalyst, the chemical

properties of the catalyst were then investigated using the Suzuki-Miyaura cross

coupling reaction. By selecting a range of substrates with varying electron

densities, it was hoped that the transformational limitations of the prepared

catalyst would be identified. A substrate scope was identified tending from using

substrates with a low electron density at the position of palladium insertion

(4-bromoacetophenone and 4-bromobenzotrifluoride) towards a substrate with

a higher electron density (4-bromoanisole).

Following a literature search a standard reaction was identified for the reaction.

To determine a comparison towards standard catalyst systems such as

palladium acetate, an initial reaction was used using palladium acetate as the

catalyst. The substrate chosen for the first reaction was 4-bromoacetophenone

whilst phenylboronic was used as the aryl boronic acid in all subsequent

reactions. The results from the experiment are shown below, and 1H NMR

spectroscopy was used to investigate the conversion and yield of the products

formed (Table 3).

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Scheme 14

Run Base Solvent Yield (%)

1 K2CO3 EtOH 82

2 K2CO3 EtOH 79

Table 3

Using 4-bromoacetophenone, the anticipated yield using palladium acetate was

expected to be high. The low electron density around the halide would

encourage palladium insertion and the yields observed reflect this. Between

Entries 1 and 2 the yield achieved was relatively high with 82 and 79%,

respectively. Following the results of the standard reaction using palladium

acetate, the catalyst prepared in the lab was used to catalyse the same reaction,

however no product conversions were detailed Having said this, it was reported

that the desired product was obtained for approximately 25% of the runs.

Continuing the investigation into the effects of electron withdrawing groups on

the yield for the Suzuki reaction, 4-bromobenzotrifluoride was selected as the

cross-coupling partner with phenylboronic acid. Table 4 indicates the reported

yield when using palladium acetate as the catalyst.

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Scheme 15

Table 4

From Table 4, the product yield appeared to fluctuate between the two Entries.

Entry 1 resulted in a significantly lower yield (69%), than Entry 2 (87%). The

strong electron withdrawing effect of the trifluoromethyl function group meant

that the oxidative addition, and palladium insertion steps to the Heck reaction

should have been favourable in this reaction system. It was assumed that the

reduced yield in Entry 1 was a result of experimental error.

When the catalyst prepared in the labaratory was used in the reaction system,

products were identified for 1 reaction out of the 31 carried out, though no

yields were reported.

The reaction between 4-bromoanisole and phenylboronic acid was used to

investigate how the yield observed with palladium acetate as the catalyst would

reduce based on the reduced electron withdrawing effect experienced by the

halide. Table 5 indicates the reported yield when using palladium acetate as the

catalyst.

Run Base Solvent Yield (%)

1 K2CO3 EtOH 69

2 K2CO3 EtOH 87

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Scheme 16

Run Base Solvent Yield (%)

1 K2CO3 EtOH 43

2 K2CO3 EtOH 48

Table 5

Using 4-bromoanisole as the selected substrate, it was anticipated that the yields

obtained would be lower than had been previously recorded using

4-bromoacetophenone and 4-bromobenzotrifluoride. From the results in Table

5, it is clear that the product yield for Entries 1 and 2 (43 and 48%) is

significantly lower than when 4-bromoacetophenone was used (82 and 79%)

and also lower than the when 4-bromobenzotrifluoride was used (69 and 87%).

The increased electron density within 4-bromoanisole resulted in a drop of in

yield as oxidative addition became more difficult for the catalyst to carry out.

When the catalyst was used the more challenging conditions appeared to affect

the success of the catalyst prepared and none of the expected product was

obtained in any of the runs.

While experiencing difficulty in obtaining products, Javier was able to recover

the catalyst easily after each reaction by filtering off the product, which was an

aim of the project.

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5. Results and Discussion

The following section shows the results obtained throughout the project.

5.1 Objectives

The objective of this project was to further develop the:

i. synthesis of a novel silica supported heterogeneous palladium catalyst,

and

ii. use the catalyst system in a series of Heck reactions to highlight its

potential as an alternative catalyst system in organometallic

transformations to traditional homogeneous reagents.

The following section will contain first a description of how the synthesis of the

catalyst was carried out and analysed, and secondly, provide details on the

catalysts performance.

However, before attempting the preparation of the palladium catalyst, an

understanding into the formation of the silica support was required. By

approaching the project in this way, it provided an opportunity for

familiarisation of the required experimental procedures and to obtain consistent

results before attempting to incorporate the metal in the catalyst system.

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5.1.1 Synthesis of the silica support

All attempts at the synthesis of the silica support were achieved following a

bioinspired approach developed from within the laboratories of Dr. Siddharth

Partwardhan, as shown in Scheme 17. A 1:1 ratio of sodium metasilicate and

PEHA were combined and dissolved in water, resulting in a basic solution (pH

13). Upon complete dissolution of the reagents, 1M aq. HCl was slowly titrated

into the solution until a consistent pH of 7 was achieved. At pH 7 the silica

precipitates out of solution as a result of the interaction between the PEHA and

the silica itself. Throughout the neutralisation, the reaction mixture was stirred

using a magnetic stirrer, and having obtained the correct final pH (6.9-7.1), the

silica support was isolated from the reaction mixture by centrifuge. Following

this, the product was washed with water to remove excess PEHA. From analysis

of previous results from within the group, the rough volume of HCl required to

reduce the solution to the correct pH was already known. It was with this

knowledge that a series of titrations were carried out to investigate the

formation of the desired silica support. Towards this aim, the reaction sequence

was repeated until three consistent results were obtained.

Scheme 17

The results shown in Table 6 indicate that when the synthesis was attempted on

a small scale (0.5 mmol), that a relatively constant mass output of ≈ 20 mg could

be achieved, with only minor variances observed (Entries 1-4). It should also be

noted that although the final pH values fluctuated slightly (between 6.91 in Entry

1 to 7.03 in Entry 2) this did not appear to affect the mass of silica isolated

significantly.

sodium metasilicate

PEHA

crude silica support silica support

1) dissolve reactants

2) mix reactants

3) reduce pH 3) oven dry

1) Centrifuge

2) 3 x H2O washes

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Table 6

Whilst working on this very small scale provided confidence that the described

procedure was in fact robust and reproducible, it unfortunately did not deliver a

realistic mass of catalyst support to provide the required material to complete a

project of this nature. At this stage, the scale of the silica produced was increased

ten-fold, and the results obtained are shown in (Table 7).

Entry

Sodium metasilicate

(mg)

PEHA (mg) Initial pH Final pH HCl (μl) Mass silica

support (mg)

1 636.0 116.0 12.58 6.91 6634 289.1

2 635.6 117.5 12.36 6.94 6615 201.6

3 636.2 116.4 12.42 6.92 6625 285.3

Table 7

The results shown in Table 7 indicate that upon increasing the scale of the

reaction, the mass of silica output varied from between 201.6 mg in Entry 2 to

289.1 mg in Entry 1. Comparing these results to that of the smaller scale

reactions, shown in Table 6, highlights the differences in isolated mass of silica

support upon scale up. In Table 6 the average mass of catalyst was ≈20 mg,

therefore by scaling up ten-fold, a mass of ≈ 200 mg was expected. From this

perspective, Entry 2 would appear to have produced an isolated mass of silica,

consistent with previous results, with 201.6 mg produced. However, Entries 1

and 3 produced significantly higher amounts of silica support (285.3 and 289.1

mg). At this stage, it is unclear if the increase in isolated mass observed was a

Entry

Sodium metasilicate

(mg)

PEHA (mg)

Initial pH Final pH HCl (μl) Mass silica

support (mg)

1 63.9 11.9 12.99 6.91 630 19

2 63.7 12.4 13.30 7.03 663 20

3 63.6 12.2 13.21 6.93 662 21

4 63.6 12.1 13.17 6.90 664 18

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result of greater reaction efficiency at scale, or if simply more of the PEHA was

present in the final silica residue, having not been washed out as effectively as

with Entry 2. These results do however highlight that the reaction appeared to

be much more sensitive at an increased scale, with yields varying significantly

despite following an identical protocol. Unfortunately, due to time constraints

further optimisation of the procedure was suspended at this time.

Having successfully prepared silica in a controlled method, the first aim of the

project had been completed, and the preparation of palladium catalyst was the

next objective.

5.1.2 Preparation of palladium nanoparticles on silica

Preliminary work from within the laboratories of Dr. Siddharth Partwardhan had

previously identified a method to prepare the palladium catalyst as shown

(Scheme 18).

Scheme 18

The main difference in protocol between the preparation of the silica support

(Scheme 17) and the silica supported palladium catalyst (Scheme 18) was that

in the latter case, the procedure required the addition of a preformed solution of

palladium acetate (Pd(OAc)2) and sodium metasilicate, to a solution of PEHA in

water, before neutralising to pH 7. Towards this aim, the palladium acetate was

initially dissolved in 5 cm3 of acetone, before combining with an aqueous

solution of sodium metasilicate. Acetone was chosen as the eluent of preference,

since previous results from within the group had indicated that Pd(OAc)2

sodium metasilicate

PEHA

Crude ProductPalladiumCatalyst

1) dissolve reactants

2) mix reactants

3) reduce pH 3) oven dry

1) Centrifuge

2) 3 x H2O washes

Pd(OAc)2 / (CH3)2CO

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dissolved in acetone formed a more homogeneous solution, compared to when

dissolved in ethanol.[31,54]

5.1.3 Synthesis of palladium catalysts

With regards to the palladium catalyst itself, it was decided at an early stage that

a relatively low loading of metal would be used in order to allow for easy

handling of the resultant product. Towards this aim, the loading that was aspired

to was 10 mol % of palladium. In an attempt to try to achieve this, 10-mol % of

palladium was added comparative to the initial amount of sodium metasilicate.

Additionally, it was recognised that although the initial loading of the metal

would be calculated using a basic molar ratio between sodium metasilicate and

palladium, that the final metal loading would be calculated retrospectively using

ICP analysis of the wastewater generated from each batch of catalyst. From

previous work, it was noted that while aspiring to a 10 mol % catalyst, the

percentage loading (% w/w) achieved was actually closer to 35% w/w. With this

knowledge in mind, catalyst preparation could be initiated.

Since a procedure was already established, the only decision to be made was the

scale at which to prepare the first batches of catalyst. Finally settling on a 5 mmol

scale with respect to sodium metasilicate, an initial set of reactions was

attempted (Table 8).

Catalyst

Batch

Sodium metasil icate

(mmols)

PEHA

(mmol)

Palladium

(mmol) Initial pH Final pH HCl (μl)

Mass of catalyst

(mg)

1

5.26

0.50

0.45

12.39

6.98

6129

324.8

2

5.21

0.51

0.44

12.36

7.01

6150

298.4

3

15.64

1.50

1.56

12.67

7.08

18000

873.8

4

15.64

1.51

1.56

12.68

7.03

17900

935.6

Table 8

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From the table above, it can be seen that the differences between Catalyst 1 and

2 are relatively small. The initial pH of the reaction mixtures were very similar,

with a difference of only 0.03 between both attempts. The final pH of the reaction

mixture was also very similar between Entries 1 and 2 with 6.98 in comparison

to 7.01, respectively. Surprisingly, however, the mass of catalyst produced in

each of the reactions did vary slightly, with Entry 1 affording 324.8 mg of catalyst

compared to an isolated mass of 298.4 mg in Entry 2. Again, the reasons for this

variation in isolated mass were not clear, but it was recognised that the

differences in mass were not different enough to justify a lengthy optimisation

sequence. Due to time constraints, it was decided to scale up the reaction to

provide the required volume of material to screen the subsequent Heck

reactions. Additionally, it was also recognised that should there be any

significant differences between the batches of catalyst produced, that this would

be discovered when further investigating the physical properties of the catalyst.

Having successfully synthesised 2 batches of catalyst, the reaction was scaled up

to prepare enough catalyst to carry out all the subsequent Heck reactions.

Hence, Batches 3 and 4 of the catalyst reflect a three-fold increases in scale of

catalyst preparation, to 15 mmol sodium metasilicate. The results shown above

compare favourably with Batches 1 and 2, with very similar initial pH values

associated with each system, 12.67 and 12.68 respectively for Batches 3 and 4.

The final pH was also similar (7.03 – 7.08) between the two. In accordance with

the scale up, the mass of catalyst isolated has increased by around three times

(298.4 - 324.8 mg for Batches 1 and 2, and 873.8 – 935.6 mg for 3 and 4).

However, a variation in the mass of catalyst isolated in Batches 3 and 4 was

observed. It should be noted, however, that similar variances were observed

from Batches 1 and 2. With time constraints in place, it was decided that having

produced enough catalyst to begin testing the reactivity of the system, we would

move on.

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5.1.3 Calcination

Calcination is the heat treatment of a material as a method to remove volatile

fractions from a material or result in a thermal deposition, or phase change of a

material. Prior to investigating the physical properties of the catalysts prepared,

they were first subjected to calcination in an air furnace. This was necessary,

since the unreacted PEHA left in the reaction mixture has a tendency to remain

in pores after oven drying, and only the increased temperature within the

furnace has the ability to evaporate the amine from the silica. This heat

treatment meant that the catalyst should result in an increase to both surface

area and pore size.[15] As a result of the calcination the mass of each catalyst

reduced as the PEHA was evaporated, the results pre and post calcination are

shown in Table 9.

Catalyst Batch

Pre-Calcination mass (mg)

Post-calcination mass (mg)

Change in mass (mg)

Change in mass (%)

1 324.8 275.4 49.4 15.21

2 298.4 247.5 50.9 17.06

3 873.8 736.8 137.0 15.68

4 935.6 804.9 130.7 13.97

Table 9

Each catalyst was subjected to the same conditions throughout the calcination,

with the furnace set to 5500C for five hours. This was to ensure that all of the

PEHA was removed from the pores of the catalysts, and Table 9 indicates the

change of mass of the catalyst due to this process. Although Catalyst 3 and 4

were prepared in a larger scale (three-fold) to Catalysts 1 and 2, the percentage

change in mass from the original pre-calcination mass is relatively constant,

scaling from 13.97% in Catalyst 4 to a maximum of 17.06% in Catalyst 2.

Catalysts 1 and 2 showed a similar change in mass (49.40 mg and 50.90 mg)

however, since the pre-calcination mass of catalyst was larger for catalyst 1, the

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change in mass represented a smaller overall change of 15.21%, while for

Catalyst 2, having a significantly lower pre-calcination mass meant that the

change in mass had a greater overall difference to the mass of catalyst and a

larger percentage change in mass of 17.06%,

Catalysts 3 and 4 experienced a similar percentage change in mass (15.68% and

13.97%) indicating that there was a similar mass of PEHA trapped in the

structure of the catalyst. Although there is a larger change in mass between

Catalysts 3 and 4 than between 1 and 2, this represents a lower percentage

difference since the catalysts prepared are on a larger scale.

These results might also indicate that the variances observed in the masses of

catalyst produced cannot be due to residual PEHA, since a consistent amount

was removed from each of the catalyst batches prepared.

It should be noted that a small amount of the catalyst prepared was not

calcinated in an effort to test the effect of the uncalcinated catalyst in direct

comparison to the calcinated catalyst, to determine if this step is necessary.

5.2 Investigating the physical properties of the catalyst

Before proceeding to investigate the overall reactivity of the final catalyst system

in organometallic transformations, one final piece of information was required,

namely, its physical properties. Towards this aim, three methods were identified

as crucial. The first of these was BET testing, as this would show the total surface

area of the catalyst as well as the specific surface area, (Equations 5-6 in Section

3.6.2). Secondly, BJH analysis would be used to investigate pore size, for both

adsorption and desorption, (Equation 8 in Section 3.6.3). Finally, ICP testing

would be carried out to estimate the quantity of the metal present within the

catalyst system. From these results we should be able to determine if the catalyst

preparation provides consistent physical properties and loading to further

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identify if the procedure is suitable or if further optimisation is required to

obtain a reliable synthesis.

5.2.1 BET testing

The first method used to investigate the physical properties of the catalyst was

BET testing. Having numbered each batch of catalyst as they were was prepared,

the batches were submitted for BET testing individually. The results obtained are

shown below in Table 10.

Catalyst Batch 1 2 3 4

Scale (mmol S.M.) 5 5 15 15

BET surface Area (m2/g) 60.3187 64.8807 120.1755 170.7142

Pore Volume (cm3/g) 0.06401 0.06976 0.03803 0.02103

Table 10

The batches of catalyst in Table 10 can be looked at separately according to the

scale at which they were synthesised. As can be seen in Table 10, Batches 1 and

2 were physically very similar to one another. Their total surface area compare

favourably, with the surface area for Batch 1 equal to 60.32 m2/g, while for Batch

2 the calculated surface area was equal to 64.88 m2/g. The difference in pore

volume between the two batches is also very small, with Batch 1 having a pore

diameter for adsorption of just 0.06401 cm3/g, while Batch 2 has a pore volume

of 0.06976 cm3/g. These results would seem to suggest that on a 5 mmol scale

for sodium metasilicate the described method allows for a relatively consistent

mass of catalyst prepared (see Table 8).

However, Batches 3 and 4 (15 mmol scale synthesis) of the catalyst appear to be

significantly different in physical properties to the smaller scale Batches of 1 and

2 (5 mmol). Firstly, in general the surface area appears to be much larger with

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120-170 m2/g observed in Batches 3 and 4 compared to 60-65 m2/ g associated

with Batches 1 and 2 of the catalyst. As a larger structure of silica had been

produced, it was expected that the surface area of Batches 3 and 4 would be

greater than the surface area of Batches 1 and 2. Additionally, the pore volumes

of the catalysts appear to be significantly different, having decreased from

around 0.064 - 0.069 cm3/g in Batches 1 and 2, to between 0.038 – 0.02103

cm3/g in Batches 3 and 4. Importantly, when taking a closer look at just Batches

3 and 4 of the catalyst, it quickly becomes clear that the present method does not

seem suitable to produce a consistent catalyst at increased scale. Notably,

despite Batches 3 and 4 having been synthesised on the same scale, the large

difference in surface area between the two is relatively striking. Hence, Batch 3

had a surface area of 120.1755 m2/g while Batch 4 had a surface area of

170.7142 m2/g. The pore volume also experiences a similar discontinuity

between observed results; with the pore volume of Batch 3 was equal to 0.03803

cm3/g, whilst, for Batch 4, the pore volume was equal to 0.02103 cm3/g.

It should be noted that, at this time, it is unclear why these physical properties

vary so widely upon increasing the scale of the reaction, resulting in an overall

increase in pore volume and surface area. There results were rather surprising

since each of the smaller scale (5 mmol) batches appeared to be very similar

both in terms of mass produced and physical properties. These results would

indicate that further investigation is required to develop a protocol that would

allow a reproducible catalyst both in terms of mass of catalyst and physical

properties. It is also unclear what the overall effect on the reactivity of the

catalyst these clear changes in physical properties would have. Unfortunately,

due to time constraints further investigation into catalyst synthesis was not

pursued.

5.2.3 ICP testing

In an effort to investigate the amount of palladium contained within the silica

support, ICP testing of the wastewater generated from each catalyst preparation

was obtained. The assumption made during testing was that any palladium that

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was not discovered in the wastewater would instead be attached to the catalyst

support. By calculating how much palladium remained in the wastewater, it

would be possible to calculate how much palladium could be found in the silica

support. The results obtained by the ICP testing are shown below in Table 11.

Table 11

The results in Table 11 show that for Batch 1 and 2 (5 mmol) that a similar

amount of palladium was found in the wastewater, Batch 1 contained 239.52

mg/l while Batch 2 contained 237.69 mg/l. This indicates that on the smaller

scale, the loading is similar and appears to be reproducible. In Batches 3 and 4

(15 mmol) the results are also fairly similar, though there is more variance

between the final two batches than the first two, Batch 4 containing 639.03 mg/l

compared with 584.73 mg/l in Catalyst 3. It should be noted however that the

significant difference in palladium values between Batches 1-2 and 3-4 is due to

the increased scale from 5 mmol to 15 mmol. Furthermore, Table 12 shows the

results after calculating the estimated percentage loading by mole of the catalyst

having calculated the palladium remaining in the silica support.

Catalyst 1 2 3 4

Scale (mmol S.M.)

5 5 15 15

Conc. palladium

(mg/l) 239.52 237.69 584.73 639.03

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Catalyst Batch

Concentration Pd in sample (mg/l)

Sample Volume (cm3)

Palladium in silica (mmol)

Percentage loading

(mol %)

1 239.52 50 0.45 10.844

2 237.69 50 0.44 12.073

3 548.73 50 1.56 15.507

4 639.02 50 1.56 13.188

Table 12

As mentioned previously (Section 5.1.3), preparation of the catalyst was

designed to produce a metal loading of 10 mol %. From Table 12 it can be seen

that the estimated percentage loading appears to be fairly close to the desired

value of 10 mol%, with Catalysts 1 – 4 showing a loading range of between

10.844% and 15.509 mol%. Looking more specifically at the results it can be

seen that some variance in loading is observed in each of the various batches

with loadings slightly higher in 3 and 4 (15 mmol) with 15.507% and 13.188%

respectively. Compared to Batch 1 and 2, with loadings calculated at 10.844%

and 12.073% respectively. However, the protocol does appear to be suitable to

provide the catalyst at the desired loading, although further optimisation is

required. The methodology for the calculation for the estimated molar loading of

the catalyst is shown in appendix 1 (Section 8).

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5.2.4 BJH analysis

The final type of analysis carried out on the prepared catalyst was BJH testing.

Used in conjunction with BET testing, BJH analysis specifically looks at the pore

diameters of a catalyst for adsorption and desorption.

Catalyst Batch 1 2 3 4

BET surface area (m2/g)

60.3187 64.8807 120.1755 170.7142

BJH adsorption (nm) 16.2253 15.6309 22.9997 17.2249

BJH desorption (nm) 20.4723 19.9013 31.4944 23.5811

Table 13

From the results presented in Table 13, it can be seen that in the smaller scale

reactions (Batches 1 and 2, 5 mmol), the pore size does appear to be relatively

similar, with a diameter for adsorption of 16.23 nm observed for Catalyst 1,

whilst a diameter of 15.63 nm was observed for Catalyst 2. This indicates that

the synthesis of the catalyst does appear robust when on the small scale (5

mmol). Importantly, for the larger scale synthesis (Catches 3 and 4, 15 mmol),

the difference in adsorption diameter was significantly different, having values of

22.9997 nm and 17.2249 nm, compared to ≈ 16 nm in Batches 1 and 2. These

results would seem to confirm that when the reaction is scaled up from 5 mmol,

to a 15 mmol scale, that significant differences in physical characteristics of the

catalyst are occurring.

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5.2.5 Conclusions

Overall, the results suggest that the current procedure for the preparation of the

catalyst is robust at a small scale (5 mmol), but less so at a larger scale (15

mmol). Further investigation is required to obtain a protocol to synthesise the

catalyst on a larger scale.

As a final comment, this project is focused on the proof of concept of bioinspired

silica and its use as a catalyst support. To avoid any variances in reactivity due to

the differences in physical properties of the catalysts, all four batches of catalyst

prepared were combined together to form a homogenised catalyst system,

before reacting them under the conditions identified in the next sectio n.

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5.3 Catalyst Testing

5.3.1 Objectives

With the silica-supported catalyst now in hand, the second objective of the

project could now be started. Towards this aim, the catalyst would be introduced

as the active catalytic ingredient to mediate an organotransition metal coupling.

More specifically, palladium has become the most versatile of transition metal

catalysts mediating a range of cross coupling reactions including Suzuki, Heck

and Negishi couplings, amongst the most commonly used in industry. As

previously mentioned, research from the group had analysed the effectiveness of

the catalyst in a series of Suzuki reactions as shown.

Scheme 19

Although some moderate success had been achieved to date, the catalyst system

was still at an early stage of development and further optimisation was required

to attain results competitive with other systems currently in the recent scientific

literature, (see Section 4).[34]

In an effort to extend the substrate scope and further illustrate the versatility of

the novel catalyst system under investigation, the Heck reaction was identified

as a suitable reaction candidate. From the outset of this project, the aim had been

to test the limits of its transformational capability. Due to the time constraints

surrounding the project, the substrate of choice had to be commercially available

and easy to purify. With this in mind, methyl acrylate was identified as an

excellent candidate, since it is well known as a reagent in Heck reactions, is

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commercially available and has a low boiling point (80oC). The final of these

qualities was off the upmost importance since, upon reaction completion, any

unreacted methyl acrylate could be easily removed at reduced pressure, leaving

only starting bromide and products. From the remaining product mixture 1H

NMR analysis should allow a ratio of product to starting materials to be

determined to give an estimation of conversions.

It was from this point, that a comprehensive literature search identified a set of

standard conditions that provided a suitable basis to test the reactivity of our

catalyst system comparative to a known system as shown in Scheme 20, Table

14. [35]

Scheme 20

Entry Catalyst Percentage

conversion (%)

1 Pd(OAc)2 85

2 Pd2(dba)3.CHCl3 75

3 Pd(OAc)2/2PPh3 100

4 Pd(OAc)2/2PPh3 97

5 Pd(OAc)2/dppe 85

6 Pd(OAc)2/dppp 86

7 Pd(OAc)2/dppf 96

Table 14

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Although the literature example was concerned with the effect of ligands on

conversions within homogeneous catalysis it did provide a standard reaction

protocol to compare the reactivity of our catalysts system to. It is from this point

that the chemical analysis of the catalyst was initiated.

In the following section the results are presented as % conversion, for clarity

these are not determined using a standard, but rather are a ratio of the

diagnostic peaks for starting material against the product peaks obtained in the

1H NMR spectrum.

4-bromoacetophenone

In their paper relating to the activity of various palladium catalysts in the Heck

reactions, the Qadir group identified that 4-bromoacetophenone could be readily

transformed under Heck conditions, using Pd(OAc)2 and Et3N in DMF at 140oC

(Scheme 21).[61] In this specific example the reaction was deemed an excellent

place to initiate the testing of our catalyst due to the simplicity of the system.

Before beginning the analysis of the novel catalyst system, a standard set of

reactions was performed. This allowed not only the identification of an optimal

set of conditions to provide high conversions, but also allow a familiarisation of

both the experimental procedure and the 1H NMR analysis of the resultant

product mixture. The results obtained from the experiments are shown in Table

15 below.

Scheme 21

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Entry Palladium

source Additive Reaction Time (h) Conversion (%)

1 Pd(OAc)2 - 24 80

2 Pd(OAc)2 - 24 100

3 Pd(OAc)2 PPh3 24 80

4 Pd(OAc)2 PPh3 24 90

5 Pd(OAc)2 - 24 95

6 Pd(OAc)2 - 24 100

Table 15

Table 15 represents an attempt to find a standard set of reaction conditions that

would allow high levels of conversions combined with simple analysis. All

reactions were carried out in a sealed vessel, heating to 140oC, for 24 hours.

Entries 1-2 represent the simplest conditions identified from the Qadis group

paper. In this case, Et3N converts the Pd(II) to Pd(0) in situ to provide the active

catalyst. Upon reaction completion Et3N is also of sufficiently low boiling point

(89oC) to allow simple removal at reduced pressure so as not to complicate the

final 1H NMR spectra. As can be seen from the results this very simple system

proved extremely successful with conversions of 80-100% observed.

Entries 3-4 represent identical reaction conditions only with the inclusion of

PPh3 as an additive. PPh3 was added for two reasons: firstly PPh3 is widely used

to reduce Pd(II) to Pd(0) under the reaction conditions. The paper by Qadis also

identified phosphine ligands as beneficial to reaction conversions hence it was

hoped that the inclusion of PPh3 would increase the efficiency of the system. The

results show that although conversions of 80-90 % were observed, no obvious

advantage was gained from the addition of phosphine additives. Furthermore,

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PPh3 has a high boiling point (3600C) and proved detrimental to 1H NMR analysis

by further complicating the resultant spectra.

From these results it was decided that the conditions to be used going forward

would be: DMF, 1400C, 24 h, Et3N, Pd(OAc)2 (10 mol %).

With these results in hand, Entries 5-6 represent further repeats of entries 1 and

2. These experiments were carried out to provide confidence that the identified

conditions were roust and reproducible. This was confirmed by conversions of

95-100 %.

5.3.2 Test of uncalcinated catalyst

To determine the effect of any PEHA remaining in the pores of the uncalcinated

catalyst, two reactions were carried out under standard conditions. These

reactions were designed specifically to determine if calcinations of the catalyst

system were necessary before deployment in organometallic reactions (Scheme

20, Table 16).

Scheme 22

Entry Palladium

source Additive Reaction Time (h) Conversion (%)

1 Pd/SiO2 - 24 95

2 Pd/SiO2 PPh3 24 <10

Table 16

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From the results it can be seen that the uncalcinated catalyst is extremely active

under certain conditions (Table 16). More specifically, Entry 1 represents the

reaction of the uncalcinated catalyst using the identified standard conditions.

Under these reaction conditions a conversion of 95% was obtained showing that

an effective catalytic system can be achieved using an uncalcinated catalyst.

However, at present it is unclear if calcination is necessary but it will be revisited

once it can be compared to calcinated results.

Entry 2 represents the effect of PPh3 on the catalyst system. From the results

obtained from the standard reactions (Table 15) it was unclear if the PPh3

would promote the reaction, have little or no effect on the reaction, or potentially

block the pores of the catalyst and slow the reaction. As can be seen from the

results in Table 16, a conversion of <10% was observed. From the results of

Entry 2, it is clear that to adding PPh3 is completely detrimental and shuts down

the catalyst system.

5.3.3 Test of calcinated catalyst

Following investigation into the activity of the uncalcinated catalyst, two

reactions were set up to directly compare the reactivity of the calcinated catalyst

under standard conditions. The results are shown below in Table 17.

Scheme 23

Entry Palladium

source Additive Reaction Time (h) Conversion (%)

1 Pd/SiO2 - 24 100

2 Pd/SiO2 - 24 100

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Table 17

It can be seen from the results that the calcinated catalyst is active under

standard conditions (Table 17). Both Entries 1 and 2 achieved extremely high

levels of conversion with 100% observed for both entries. Comparing these

results to the reactivity of the uncalcinated catalyst (Table 16), it was observed

that the level of conversion was only marginally better than the uncalcinated

catalyst (95%, Entry 1, Table 16).

The results obtained in Table 17 can also be compared to the standard reactions

using unsupported palladium acetate. With this in mind, conversions obtained in

Table 17 for both Entries 1 and 2 (100%) compared favourably to the results

obtained in Table 14 with unsupported palladium acetate (80-100%). These

results also indicate that the catalyst prepared in the laboratory is at least as

effective as unsupported palladium acetate in the conversion of 4-

bromoacetophenone.

Having successfully concluded that the calcinated catalyst prepared in the

laboratory was effective within the Heck reaction system, it was decided to

investigate whether different substrates would affect the level of conversion, and

ultimately, the effectiveness of the catalyst within the Heck reaction.

5.3.3 Substrate Scope

Having proven that the catalyst system is reactive under standard reaction

conditions, a range of alternative coupling partners were examined. To begin this

expansion of substrate scope, a variety of aryl halides were examined, beginning

with electron deficient and tending towards more difficult, electron rich

substrates. By changing the electronics of the coupling partner a relative

examination of the activity of the catalyst could be determined.

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From this point of view electron deficient systems are known to be highly

reactive systems since the oxidative addition step of the Heck reaction occurs

readily in these substrates. As the aryl halide becomes increasing electron rich or

sterically encumbered, the oxidative insertion step should become more difficult

and hence only a highly reactive catalyst will succeed in catalysing these

reactions.

5.3.4 Electronic Effects on the Heck Reaction

Table 18 represents the relative product conversions associated with the

various aryl halides when the calcinated catalyst was reacted under standard

conditions, (Scheme 24).

Scheme 24

Entry R1 R2 Reaction time Conversion

1 -CF3 Br 24 > 95

2 -CF3 Br 24 100

3 -COCH3 Br 24 100

4 -COCH3 Br 24 100

5 -CH3 Br 24 50

6 -CH3 Br 24 40

7 -COCH3 Cl 24 < 10

8 -COCH3 Cl 24 0

Table 18

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Entries 1 and 2 represent the results obtained whilst using

4-bromobenzotriflouride as the substrate. With the three fluorine atoms at the

same end of the benzene ring, an area of electron density will occur as a result of

the dipole caused by the highly electronegative fluorine atoms. As a result of the

dipole the oxidative addition step of the Heck reaction should become easier,

making the substrate more reactive compared to electron rich substrates. From

Table 18, the results indicate that the catalyst activity was high with product

conversions of 95% and 100% observed. Comparing these results to Entries 3

and 4 (4-bromoacetophenone), it can be seen that in a slightly more electron rich

system, the catalyst also performed well, obtaining 100% conversion for both

attempts. It was anticipated from the outset that the overall conversion of

Entries 1-4 would be relatively high, and the results between these substrates

endorse the hypothesis.

In Entries 5 and 6 the substrate used was 4-bromotoluene. Having used strongly

electron-withdrawing groups up to this point it was anticipated that this

coupling partner would represent a more difficult test for the catalyst.

Accordingly, the product conversions were reduced to 40 and 50% for Entries 5

and 6 with this coupling partner. With regards to the level of product

conversion, the catalyst was successful in transforming some of the substrate to

the desired product, under standard conditions. This result indicates that the

catalyst prepared is robust enough that it is not restricted to substrates

containing beneficial electron withdrawing groups, however it appears that

optimisation of the reaction is required to improve conversions further. With

this in mind, conversions may improve with prolonged reaction times.

The final substrate used was 4-chloroacetophenone (Entries 7 and 8), which

represented a different type of challenge for the palladium catalyst. As

previously mentioned the carbonyl group is an electron-withdrawing group,

however, the chlorine atom is not as effective a leaving group as bromine in

4-bromoacetophenone. Bromine is an excellent leaving group because it does not

form particularly strong bonds with carbon (288 kJ/mol) and has a longer bond

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length (194 pm) than the equivalent chlorine-carbon bond (177 pm).

Accordingly, the shorter bond length associated with the chlorine-carbon bond is

indicative that the overlap of the bonding orbitals between the two atoms is

better than that of the bromine-carbon bond, and hence the overall bond energy

for the chlorine-carbon bond is higher (330 kJ/mol) than that of the bromine-

carbon bond. Taking this information into account, the oxidative addition step

would be expected to be more difficult and hence a lower reactivity was

expected to be observed.

From Table 18, it can be seen that as expected a lower level of conversion was

achieved for Entries 7 and 8 (< 10% and 0 respectively). Although expected, the

low conversion figures achieved by the palladium catalyst for 4-

chloroacetophenone were nonetheless slightly disappointing. However, A.C.

Hillier et al., discovered that while using aryl chloride substrates in the Heck

reaction, “no activity was observed”.[62] With this in mind, and understanding

that aryl chlorides are tough cross-coupling partners, we decided to move on to

allow sufficient time to investigate the effect of steric hindrance and catalyst

loading to the reaction.

5.3.5 Steric effects on the Heck reaction

Having investigated if varying the electronics on the aryl halide affects product

conversions, it was decided that the steric effects should also be analysed. Since

4-bromoacetophenone was known to be a highly effective substrate, it was

decided that 2-bromoacetophenone would be used to investigate how steric

hindrance would affect performance of the catalyst under standard conditions.

From the investigation into the electronic effects on the Heck reaction the

observed conversions would allow a direct comparison between the substrate

chosen (2-bromoacetophenone) and the previous results obtained (Scheme 25).

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Scheme 25

Entry Substrate Reaction Time Conversion

1 2-bromoacetophenone 24 0

Table 19

From Table 19 we can see that there was no reaction was observed with 2-

bromoacetophenone. This result can be directly compared to the conversion

associated with 4-bromoacetophenone (100 %, Table 17, Entry 1) From this

result it can be determined that increased steric hindrance around the carbon-

halide bond would appear to inhibit reaction progress. Due to the complete

failure of this reaction further investigations were suspended at this time.

Having investigated the difference in percentage conversion between two

sterically different regioisomers, and under time constraints, it was decided that

it was important to move on to an investigation into the loading of the catalyst

before the supply of the prepared catalyst was exhausted.

5.3.6 Investigation into the effects of catalyst loading

From the outset of this project, it was hoped that the catalyst could be recyclable

for multiple reactions as had been possible in the previous investigations

involving Suzuki reactions (see section 4). However, when using DMF as a

solvent it immediately became clear that recycling the catalyst was not going to

be a facile process. With this in mind, it was decided to investigate if the loading

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of the catalyst could be decreased significantly for the purposes of reducing cost

and chemical waste of the system, but without reducing overall activity.

Furthermore, throughout the investigations, the presence of the catalytically

inactive palladium black was suspected. With this in mind, it seemed of

paramount importance for future work to attempt to reduce or prevent its

formation. A literature search indicated that high catalyst loadings can

encourage the formation of palladium black, and also that the leaching of

palladium into reaction mixtures results in its formation.[37] In an attempt to

address this problem, it was hoped that by reducing the loading of the catalyst, a

reduction in palladium black formation would occur. Towards this aim, two

separate catalyst loadings were used, 2.5 mol% and 1.25 mol% (Table 20,

Scheme 26).

Scheme 26

Entry Catalyst Loading

(mol%)

Reaction

Time Conversion

1 2.50% 24 100

2 1.25% 24 100

Table 20

From the results shown in Table 20, it is clear that reducing the loading of the

catalyst had little or no effect on the overall conversion to the products. Prior to

starting this experiment, it had been thought that to achieve similar conversions

at a lower catalyst loading, the reaction times may have had to be increased.

However, TLC analysis of the reaction mixture indicated that after 24 hours both

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reactions had gone to completion. Importantly, within the reaction mixture there

was no visible palladium black. This was of paramount importance since in all

previous reactions the mixture had to be filtered through celite before

separating. The success of the reduced loading may suggest that while testing the

effects of electronics and steric hindrance of the substrates on the catalyst, the

reaction mixtures could have been slightly saturated by palladium. To confirm

this, further investigation into the effects of catalyst loading is required.

5.4 Conclusions

Overall, the novel palladium doped catalyst prepared has proven to be very

active both at higher and lower loadings. Using substrates with electron-

withdrawing substituents such as 4-bromoacetophenone and 4-

bromobenzotrifluoride resulted in the highest conversions to products. As the

substrate scope moved into increasingly electron-rich systems, such as 4-

bromotoluene, moderate levels of conversion were achieved (40-50%). It would

also appear that this catalyst system is not applicable to aryl chlorides, or

sterically congested substrates. Under the current standard conditions, it would

appear that recycling the catalyst is not a viable option without further

modifications of either the catalyst or the reaction conditions.

This project was undertaken in an effort to prove that a cheap, reliable,

palladium catalyst could be prepared under mild conditions and be effective in

the cross-coupling Heck reaction, and to this end the experimentation has been

successful.

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6. Future work

This project aimed to prove the concept that a bioinspired silica based palladium

catalyst could be used efficiently to catalyse the Heck reaction. However,

throughout the project there were certain areas that could not be optimized

effectively. The preparation of silica, and the variances between physical

properties of the batches of catalyst prepared throughout this project in

particular should be thoroughly reinvestigated to identify a protocol that

produces a consistent form of catalyst at increased scale. From this standpoint, it

is clear that until consistent batches of catalyst can be produced gaining

consistent results in chemical transformations is always going to be difficult.

A significant difficulty in this project was the inability to recycle the catalyst after

each experiment. Perhaps future work could involve the screening of several

solvent systems that may allow easier recycling of the catalyst. Significantly, it

also appeared that the formation of palladium black may be an issue. Further

investigation should involve loading studies that includes the addition of both

less catalyst to the reaction mixture, and also having a significantly lower metal

loading within the silica support. By developing a catalyst that can be recycled,

future studies should involve ICP analysis of the products to determine the levels

of palladium leaching.

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7. Experimental

7.1 General

All reagents used were obtained from commercial suppliers and were used with

no further purification.

Calcination of the catalyst was carried out in an open-air tube furnace at 5500C

for 8 hours with a variation of 100C per minute when warming up and cooling

down.

ICP analysis was carried out using an Agilent Technologies 7700 Series ICP-MS.

50 ml of the reaction mixture and wastewater were submitted for analysis.

BET and BJH analysis were carried out using a micromeritics ASAP 2520. For

each batch of catalyst, a 25 mg sample was submitted for analysis.

Thin layer chromatography was carried out using Camlab silica plates coated

with fluorescent indicator UV254. The plates were analysed using a Mineralight

UVGL-25 lamp and further developed using vanillin solution.

1H NMR spectra were recorded using either a Bruker DPX-500 at 500 MHz, or a

Bruker DPX-400 at 400 MHz. The chemical shifts are reported in ppm, whilst the

coupling constants are reported in Hz and refer to 3JH-H interactions unless

otherwise specified.

7.2 General Procedures

7.2.1 General Procedure A: Preparation of silica catalyst support

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Into a centrifuge tube, sodium metasilicate was dissolved in water (Solution A).

In a separate sample tube, pentaethylenehexamine was dissolved in water

(Solution B). Solution B was mixed with solution A, and a magnetic stirrer bar

was added. The pH was recorded and the mixture was then neutralised using

HCl. By a process of co-precipitation the silica crashed out of the reaction

mixture and having reached a pH of 6.9 – 7.1 the reaction mixture was

centrifuged at 8000 rpm for 15 minutes. The silica recovered was removed from

the centrifuge and rinsed with distilled water. The reaction mixture was

centrifuged again at 8000 rpm for 15 minutes to allow all silica to be recovered.

This process was carried out a further two times. The wastewater and reaction

mixture were collected for ICP analysis. The silica prepared was dried in an oven

at 800C for 3 hours.

7.2.2 General Procedure B: Preparation of catalyst

In a beaker, sodium metasilicate was dissolved in distilled water (Solution A). In

a separate beaker, pentaethylenehexamine was dissolved in distilled water

(Solution B). At the same time, palladium acetate was dissolved in acetone in a

sample tube, before being added to Solution A. Solution B was then mixed with

Solution A, and a magnetic stirrer was added. Noting the initial pH of the reaction

mixture, HCl was then pipetted drop wise into the mixture to neutralise the pH.

By a process of co-precipitation the silica crashed out of the reaction mixture

with the palladium nanoparticles incorporated within the structure of the silica.

When the pH had reduced to between 6.9 and 7.1, the reaction mixture was

centrifuged at 8000 rpm for 15 minutes. The catalyst recovered was removed

from the centrifuge and rinsed with distilled water. The reactio n mixture was

centrifuged again at 8000 rpm for 15 minutes to allow all catalyst to be

recovered. This process was carried out a further two times. The wastewater and

reaction mixture were collected for ICP analysis. The catalyst recovered was

dried in an over for 3 hours at 1400C. The mass of the dried catalyst was then

recorded.

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7.2.3 General Procedure C: Calcination of the prepared catalyst

The prepared catalyst was spread evenly in a rectangular crucible. The crucible

was then calcinated in an open-air furnace for 8 hours at 5500C. The temperature

was increased at a rate of 100C per min, and the furnace was cooled at the same

rate. The final calcinated mass of the catalyst was recorded.

7.2.3 General Procedure D: Standard Reaction for testing

In a 10 ml microwave tube, palladium was added with triethylamine for 10

minutes and heated gently to 400C using an oil bath. Following this, the chosen

substrate was added with methyl acrylate and DMF before sealing the

microwave tube for 24 hours and increasing the temperature to 1400C. When

working up the products, the reaction mixture was filtered through celite and

washed through using DCM, before washing the DMF from the mixture by

separating with brine in a separator funnel. A rotavapor was then used to

evaporate off the methyl acrylate and DCM. The product obtained was dissolved

in chloroform before being submitted for 1H NMR analysis.

7.2.4 General Procedure E: Standard Reaction with additive PPh3

In a 10 ml microwave tube, palladium acetate was added to PPh3 and DMF. The

solution was then heated gently to 400C for 10 minutes using an oil bath.

Following this, the chosen substrate was added with methyl acrylate, Et3N and

before sealing the microwave tube for 24 hours and increasing the temperature

to 1400C. The reaction mixture was filtered through celite and washed through

using DCM, before washing the DMF from the mixture by separating with brine

in a separating funnel. A rotavapor was then used to evaporate the unreacted

methyl acrylate and DCM. The product obtained was dissolved in deuterated

chloroform before being submitted for 1H NMR analysis.

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7.3 Synthesis of silica support

Following General Procedure A, results are reported as a) amount of sodium

metasilicate, b) volume of distilled water in Solution A, c) amount of PEHA, d)

volume of distilled water Solution B, e) volume of HCl, f) reaction time, g) mass of

product.

Table 6, Entry 1:

a) 63.6 mg, 0.5 mmol, b) 5ml, c) 11.9 mg, 0.05 mmol, d) 4ml, e) 630 μl,

f) 10 minutes, g) 19 mg.

Table 6, Entry 2:

a) 63.7 mg, 0.5 mmol, b) 5ml, c) 12.4 mg, 0.05 mmol, d) 4ml, e) 663 μl,

f) 10 minutes, g) 20 mg.

Table 6, Entry 3:

a) 63.6 mg, 0.5 mmol, b) 5ml, c) 12.2 mg, 0.05 mmol, d) 4ml, e) 662 μl,

f) 10 minutes, g) 21 mg.

Table 6, Entry 4:

a) 63.6 mg, 0.5 mmol, b) 5ml, c) 12.1 mg, 0.05 mmol, d) 4ml, e) 664 μl,

f) 10 minutes, g) 18 mg.

Table 7, Entry 1:

a) 636.0 mg, 5 mmol, b) 50 ml, c) 116.0 mg, 0.5 mmol, d) 40 ml, e) 6634 μl,

f) 10 minutes, g) 289.1 mg.

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66

Table 7, Entry 2:

a) 636.6 mg, 5 mmol, b) 50 ml, c) 117.5 mg, 0.5 mmol, d) 40 ml, e) 6615 μl,

f) 10 minutes, g) 201.6 mg.

Table 7, Entry 3:

a) 636.2 mg, 5 mmol, b) 50 ml, c) 116.4 mg, 0.5 mmol, d) 40 ml, e) 6625 μl,

f) 10 minutes, g) 285.3 mg

7.4 Synthesis of palladium catalyst

Following General Procedure B, results are reported as a) amount of sodium

metasilicate, b) volume of distilled water in Solution A, c) amount of PEHA, d)

volume of distilled water Solution B, e) amount of palladium acetate, f) volume of

acetone, g) volume of HCl required, h) reaction time, i) uncalcinated mass, j)

calcinated mass

Table 8, Entry 1

a) 642.0 mg, 5.26 mmol, b) 50 ml c) 117.9 mg, 0.507 mmol, d) 40 ml

e) 100.1 mg, 0.4459 mmol f) 5 ml g) 6129 μl, h) 10 min, i) 324.8 mg,

j) 298.4 mg.

Table 8, Entry 2

a) 636.5 mg, 5.21 mmol, b) 50 ml c) 118.1 mg, 0.508 mmol, d) 40 ml

e) 99 mg, 0.4409 mmol f) 5 ml g) 6150 μl, h) 10 min, i) 298.4 mg,

j) 247.5 mg.

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67

Table 8, Entry 3

a) 1908.6 mg, 15.64 mmol, b) 150 ml c) 348.8 mg, 1.501 mmol, d) 120 ml

e) 351.1 mg, 1.56 mmol f) 15 ml g) 18000 μl, h) 10 min, i) 873.8 mg,

j) 735.8 mg.

Table 8, Entry 4

a) 1909.1 mg, 15.64 mmol, b) 150 ml c) 350.22 mg, 1.507 mmol, d) 120

ml, e) 351.1 mg, 1.56 mmol f) 15 ml g) 18000 μl, h) 10 min, i) 935.6 mg,

j) 804.9 mg.

7.5 Calcination of prepared catalyst

Following General procedure D, the results were reported as a) pre-calcination

mass, b) post-calcination mass, c) change in mass, d) percentage change in mass.

Table 9, Entry 1

a) 324.8 mg, b) 275.4 mg, c) 49.4 mg, d) 15.21 %

Table 9, Entry 2

a) 298.4 mg, b) 247.5 mg, c) 50.9 mg, d) 17.06 %

Table 9, Entry 3

a) 873.8 mg, b) 736.8 mg, c) 137.0 mg, d) 15.68 %

Table 9, Entry 4

a) 935.6 mg, b) 804.9 mg, c) 130.7 mg, d) 13.97 %

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7.6 Determination of Standard reaction conditions

7.6.1 Synthesis of methyl 3-(4-acetylphenyl)acrylate

1H NMR (500 MHz, CDCL3):

δ 7.88 (d, 2H, J = 8.3 Hz, ArH), 7.63 (d, 1H, J = 16.1 Hz) 7.50 (d, 2H, J = 8.3 Hz,

ArH), 6.40 (d, 1H, J = 16.1 Hz, CH), 3.75 (s, 3H, CH3), 2.53 (s, 3H, OCH3).

Following General Procedure D, results are reported as; a) amount of palladium

acetate, b) amount of 4-bromoacetophenone, c) volume of methyl acrylate, d)

volume of Et3N, e) volume of DMF, f) reaction time, g) reaction temperature, h)

substrate conversion.

Table 15: Entry 1

a) 0.01122 g, 0.5 mmol, b) 0.1099 g, 1 mmol, c) 0.418 ml, 3 mmol,

d) 0.272 ml, 3 mmol, e) 3 ml f) 24 hours, g) 1400C, h) 80 %.

Table 15: Entry 2

a) 0.01122 g, 0.5 mmol, b) 0.1099 g, 1 mmol, c) 0.418 ml, 3 mmol,

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C , h) 100 %.

Following General Procedure E, the results are reported as; a) amount of

palladium acetate, b) amount of 4-bromoacetophenone, c) amount of PPh3, d)

volume of methyl acrylate, e) volume of Et3N, f) volume of DMF, g) reaction time

h) reaction temperature, i) substrate conversion.

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69

Table 15: Entry 3

a) 0.01122 g, 0.5 mmol, b) 0.1099 g, 1 mmol, c) 0.26229 g, 1 mmol

d) 0.418 ml, 3 mmol, e) 0.272 ml, 3 mmol, f) 3 ml, g) 24 hours h) 1400C,

i) 80 %.

Table 15: Entry 4

a) 0.01122 g, 0.5 mmol, b) 0.1099 g, 1 mmol, c) 0.26229 g, 1 mmol

d) 0.418 ml, 3 mmol, e) 0.272 ml, 3 mmol, f) 3 ml, g) 24 hours h) 1400C,

i) 90 %.

Following General Procedure D, results are reported as; a) amount of palladium

acetate, b) amount of 4-bromoacetophenone, c) volume of methyl acrylate, d)

volume of Et3N, e) volume of DMF, f) reaction time, g) reaction temperature, h)

substrate conversion.

Table 15: Entry 5

a) 0.01122 g, 0.5 mmol, b) 0.1099 g, 1 mmol, c) 0.418 ml, 3 mmol,

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 95 %.

Table 15: Entry 6

a) 0.01122 g, 0.5 mmol, b) 0.1099 g, 1 mmol, c) 0.418 ml, 3 mmol,

d) 0.272 ml, 3mmol, e) 3 ml, f) 24 hours g) 1400C, h) 100 %.

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7.7 Testing of uncalcinated catalyst

7.7.1 Synthesis of methyl 3-(4-acetylphenyl)acrylate

1H NMR (500 MHz, CDCL3):

δ 7.88 (d, 2H, J = 8.3 Hz, ArH), 7.63 (d, 1H, J = 16.1 Hz) 7.50 (d, 2H, J = 8.3 Hz,

ArH), 6.40 (d, 1H, J = 16.1 Hz, CH), 3.75 (s, 3H, CH3), 2.53 (s, 3H, OCH3).

Following General Procedure D, results are reported as; a) amount of catalyst, b)

amount of 4-bromoacetophenone, c) volume of methyl acrylate, d) volume of

Et3N, e) volume of DMF, f) reaction time, g) reaction temperature, h) substrate

conversion.

Table 16: Entry 1

a) 0.1122 g, (10 mol %), b) 0.19905 g, 1 mmol, c) 0.418 ml, 3 mmol,

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 95%.

Following General Procedure E, the results are reported as; a) amount of catalyst,

b) amount of 4-bromoacetophenone, c) amount of PPh3, d) volume of methyl

acrylate, e) volume of Et3N, f) volume of DMF, g) reaction time h) reaction

temperature, i) substrate conversion.

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Table 16: Entry 2

a) 0.1122 g, 10 mol %, b) 0.109905 g, 1 mmol, c) 0.26229 g, 1 mmol, d)

0.418 ml, 3 mmol, e) 0.272 ml, 3 mmol, f) 3 ml, g) 24 hours h) 1400C,

i) <10 %.

7.8 Test of Calcinated Catalyst

7.8.1 Synthesis of methyl 3-(4-acetylphenyl)acrylate

1H NMR (500 MHz, CDCL3):

δ 7.88 (d, 2H, J = 8.3 Hz, ArH), 7.63 (d, 1H, J = 16.1 Hz) 7.50 (d, 2H, J = 8.3 Hz,

ArH), 6.40 (d, 1H, J = 16.1 Hz, CH), 3.75 (s, 3H, CH3), 2.53 (s, 3H, OCH3).

Following General Procedure D, results are reported as; a) amount of catalyst, b)

amount of 4-bromoacetophenone, c) volume of methyl acrylate, d) volume of

Et3N, e) volume of DMF, f) reaction time, g) reaction temperature, h) 100 %.

Table 17: Entry 1

a) 0.1122 g, (10 mol %), b) 0.19905 g, 1 mmol, c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 100 %.

Table 17: Entry 2

a) 0.1122 g, (10 mol %), b) 0.19905 g, 1 mmol, c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 100%.

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72

7.9 Investigation into the Effects of electronics on the Heck Reaction

7.9.1 Synthesis of methyl 3-(4-(trifluoromethyl)phenyl)acrylate

1H NMR (500 MHz, CDCL3):

δ 7.72 (d, 2H, J = 16.0 Hz, ArH), 7.66 – 7.61 (m, 4H, J = 12.0 Hz, ArH), 6.53 (d, 1H,

16.0 Hz, CH), 3.83 (s, 3H, CH3),

Following General Procedure D, results are reported as; a) amount of catalyst,

b) volume of 4-bromobenzenetrifluoride, c) volume of methyl acrylate, d)

volume of Et3N, e) volume of DMF, f) reaction time, g) reaction temperature, h)

substrate conversion.

Table 18: Entry 1

a) 0.1122 g, 10 mol %, b) 0.1406 g, 1 mmol, c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 95 %.

Table 18: Entry 2

a) 0.1122 g, 10 mol %, b) 0.1406 g, 1 mmol, c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 100 %.

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73

7.9.2 Synthesis of methyl 3-(4-acetylphenyl)acrylate

1H NMR (500 MHz, CDCL3):

δ 7.88 (d, 2H, J = 8.3 Hz, ArH), 7.63 (d, 1H, J = 16.1 Hz) 7.50 (d, 2H, J = 8.3 Hz,

ArH), 6.40 (d, 1H, J = 16.1 Hz, CH), 3.75 (s, 3H, CH3), 2.53 (s, 3H, OCH3).

Following General Procedure D, results are reported as; a) amount of catalyst, b)

amount of 4-bromoacetophenone, c) volume of methyl acrylate, d) volume of

Et3N, e) volume of DMF, f) reaction time, g) reaction temperature, h) substrate

conversion.

Table 18: Entry 3

a) 0.1122 g, 10 mol %, b) 0.199 g, 1 mmol, c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 100 %.

Table 18: Entry 4

a) 0.1122 g, 10 mol %, b) 0.199 g, 1 mmol, c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 100 %.

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74

7.9.3 Synthesis of methyl 3-(p-tolyl)acrylate

1H NMR (400 MHz, CDCL3):

δ 7.71 (d, J = 16.0 Hz, 1H, CH), 7.39 (d, J = 8.3 Hz, ArH), 7.06 (d, 2H, J = 8.2 Hz,

ArH), 6.40 (d, 1H, J = 16.0 Hz, CH), 3.82 (s, 1H, CH), 2.39 (s, 3H, OCH3).

Following General Procedure D, results are reported as; a) mass of catalyst,

b) mass of 4-bromotoluene, c) volume of methyl acrylate, d) volume of Et3N, e)

volume of DMF, f) reaction time, g) reaction temperature, h) substrate

conversion.

Table 18: Entry 5

a) 0.1122 g, 10 mol %, b) 0.1406 mg, 1 mmol c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 50 %.

Table 18: Entry 6

a) 0.1122 g, 10 mol %, b) 0.1406 mg, 1 mmol c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 40 %.

7.9.4 Synthesis of methyl 3-(4-acetylphenyl)acrylate

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75

1H NMR (500 MHz, CDCL3):

δ 7.88 (d, 2H, J = 8.3 Hz, ArH), 7.63 (d, 1H, J = 16.1 Hz) 7.50 (d, 2H, J = 8.3 Hz,

ArH), 6.40 (d, 1H, J = 16.1 Hz, CH), 3.75 (s, 3H, CH3), 2.53 (s, 3H, OCH3).

Following General Procedure D, results are reported as; a) mass of catalyst,

b) volume of 4-chloroacetophenone, c) volume of methyl acrylate, d) volume of

Et3N, e) volume of DMF, f) reaction time, g) reaction temperature,

h) substrate conversion

Table 18: Entry 7

a) 0.1122 g, 10 mol %, b) 0.199 g, 1 mmol c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) < 10 %.

Table 18: Entry 8

a) 0.1122 g, 10 mol %, b) 0.199 g, 1 mmol c) 0.418 ml, 3 mmol,

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 0 %.

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76

7.9.5 Investigation into the effect of steric hindrance on the Heck Reaction

Attempted Synthesis of methyl 3-(2-acetylphenyl)acrylate

Following General Procedure D, results are reported as; a) amount of catalyst, b)

amount of 2-bromoacetophenone, c) volume of methyl acrylate, d) volume of

Et3N, e) volume of DMF, f) reaction time, g) reaction temperature,

h) substrate conversion.

Table 19: Entry 1

a) 0.1122 g, (10 mol %), b) 0.199 g, 1 mmol, c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 0 %.

7.10 Investigation into the effects of catalyst loading

7.10.1 Synthesis of methyl 3-(4-(trifluoromethyl)phenyl)acrylate

1H NMR (500 MHz, CDCL3):

δ 7.72 (d, 2H, J = 16.0 Hz, ArH), 7.66 – 7.61 (m, 4H, J = 12.0 Hz, ArH), 6.53 (d, 1H,

16.0 Hz, CH), 3.83 (s, 3H, CH3),

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77

Following General Procedure D, results are reported as; a) amount of catalyst,

b) volume of 4-bromobenzenetrifluoride, c) volume of methyl acrylate, d)

volume of Et3N, e) volume of DMF, f) reaction time, g) reaction temperature h)

product conversion.

Table 20: Entry 1

a) 0.0281 g, (2.5 mol %), b) 0.1406 g, 1 mmol, c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 100 %.

Table 20: Entry 2

a) 0.0140 g, (1.25 mol %), b) 0.1406 g, 1 mmol, c) 0.418 ml, 3 mmol

d) 0.272 ml, 3 mmol, e) 3 ml, f) 24 hours, g) 1400C, h) 100%.

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8. Appendix 1

8.1 Calculating the molar loading of the catalyst

Having obtained an ICP analysis of the wastewater from each batch of catalyst,

the percentage loading of the catalyst was calculated from the concentration of

palladium remaining in the wastewater. The calculations for each of the four

batches were identical, however catalyst 1 will be looked at in detail at this point.

Catalyst

Batch

Concentration

palladium in

sample (mg/l)

Volume of sample

(cm3)

Total volume of

wastewater

(cm3)

1 239.52 50 62.5

Table 1

Assuming a uniform concentration of palladium in the total wastewater from the

reaction, the volume of wastewater can be used to calculate the number of moles

of palladium in wastewater.

Since the palladium is in the form of palladium acetate, the molar mass used for

the palladium in the system was 224.05 amu. The number of mmols palladium in

the wastewater was calculated by firstly calculating the concentration per cm3 of

palladium;

𝑛 = 𝑐

𝑣

𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑖𝑛𝑚𝑔

𝑙= 239.52

𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑖𝑛𝑚𝑔

𝑚𝑙= 𝟎.𝟐𝟑𝟗𝟓𝟐

𝒎𝒈

𝒄𝒎𝟑

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79

Since total volume of sample is equal to 62.5 cm3, and assuming the

concentration throughout the wastewater is constant then the mass of palladium

is equal to;

0.23952𝑚𝑔

𝑐𝑚3∗ 62.5 𝑐𝑚3 = 𝟏𝟒.𝟗𝟕 𝒎𝒈

The number of moles of palladium in the wastewater was then calculated by;

𝑛 =𝑚

𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠

𝑛 =14.97 𝑚𝑔

224.5 𝑔= 𝟎.𝟎𝟔𝟕 𝒎𝒎𝒐𝒍

Since we know the number of moles of palladium input into the reaction system,

we can use the principle of molar conservation to calculate the number of moles

of palladium remaining in the system.

Moles of palladium input into reaction system = 0.45 moles

𝑛𝑃𝑑 𝑖𝑛 𝑠𝑖𝑙𝑖𝑐𝑎 = 0.45 𝑚𝑚𝑜𝑙 − 0.067 𝑚𝑚𝑜𝑙 = 𝟎.𝟑𝟖𝟑 𝒎𝒎𝒐𝒍

Since we known the number of moles of palladium in the system and we know

the mass of the catalyst prepared, we can calculate the number of moles of silica

within the catalyst;

Mass of catalyst = 275.4 mg

Molar mass silica = 60.08 amu

𝑚𝑎𝑠𝑠 𝑜𝑓 𝑝𝑎𝑙𝑙𝑎𝑑𝑖𝑢𝑚 𝑖𝑛 𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡 = 0.383 𝑚𝑚𝑜𝑙 ∗ 224.5 𝑚𝑔 = 85.98 𝑚𝑔

𝑡ℎ𝑒𝑟𝑒𝑓𝑜𝑟𝑒,𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑖𝑙𝑖𝑐𝑎 = 275.4 𝑚𝑔 − 85.98 𝑚𝑔 = 189.42 𝑚𝑔

𝑛𝑠𝑖𝑙𝑖𝑐𝑎 =189.42 𝑚𝑔

60.08 𝑚𝑔= 𝟑.𝟏𝟓𝟐 𝒎𝒎𝒐𝒍

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80

Therefore the total number of moles of catalyst can be calculated, assuming there

are no impurities in the system, and finally the percentage loading of the catalyst

can be calculated;

𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡 = 3.152 𝑚𝑚𝑜𝑙 + 0.383 𝑚𝑚𝑜𝑙 = 𝟑. 𝟓𝟏

= 𝟑.𝟓𝟑𝟓 𝒎𝒎𝒐𝒍

% 𝒍𝒐𝒂𝒅𝒊𝒏𝒈 𝒐𝒇 𝒄𝒂𝒕𝒂𝒍𝒚𝒔𝒕 = 0.383 𝑚𝑚𝑜𝑙

3.535 𝑚𝑚𝑜𝑙∗ 100

= 𝟏𝟎.𝟖𝟒 %

The full table of results for the 4 catalysts is shown below, including the

calculated molar loadings.

Catalyst

batch

Pd input

to batch

(mmol)

Pd remaining

in Batch

(mmol)

mmols

of

silica

Total

number of

moles

% Loading

(mole)

1 0.45 0.383 3.152 3.538 10.844

2 0.44 0.374 2.726 3.1 12.073

3 1.56 1.335 7.288 8.622 15.507

4 1.56 1.298 8.559 9.857 13.186

Table 2

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81

8.2 Calculating loading of the catalyst (% w/w)

Using the same example as above (Catalyst 1), the loading of the catalyst (%

w/w) can be calculated, as above, by firstly investigating the mass of palladium

remaining in the silica support. (Table 3)

Catalyst

Batch

concentration

palladium in

sample (mg/l)

volume of sample

(cm3)

Total volume of

wastewater

(cm3)

1 239.52 50 62.5

Table 3

From the results detailed in Table 3, we recognize that the mass of palladium

within the system is equal to;

0.23952𝑚𝑔

𝑐𝑚3∗ 62.5 𝑐𝑚3 = 𝟏𝟒.𝟗𝟕 𝒎𝒈

From the principle of conservation of mass we know that the palladium not in

the waste stream must remain in the silica support, we can calculate the

palladium remaining in the silica by;

𝑚𝑎𝑠𝑠 𝑜𝑓 𝑝𝑎𝑙𝑙𝑎𝑑𝑖𝑢𝑚 𝑟𝑒𝑚𝑎𝑖𝑛𝑖𝑛𝑔 𝑖𝑛 𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡 = 100.83 𝑚𝑔 − 14.97 𝑚𝑔

= 𝟖𝟓.𝟖𝟔 𝒎𝒈

Since we already know the total mass of the catalyst (275.4 mg), the percentage

loading (% w/w) can be calculated by;

𝑝𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑙𝑜𝑎𝑑𝑖𝑛𝑔 (% 𝑤

𝑤) = (85.86 𝑚𝑔 ÷ 275.4 𝑚𝑔 ) ∗ 100

= 31.18 %

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82

The percentage loading for each catalyst (% w/w) was calculated for each

catalyst, (Table 4).

Catalyst Batch mass of palladium in

batch (mg) total mass catalyst

Percentage loading (% w/w)

1 85.863 275.4 31.25

2 83.737 247.5 33.91

3 299.069 736.8 40.68

4 290.781 804.9 36.21

Table 4

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9. Appendix 2

Figure 9.2.1 : 1H NMR of Synthesis of methyl 3-(4-acetylphenyl)acrylate (Table 17: Entry 1)

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84

Figure 9.2.2 : 1H NMR of methyl 3-(4-(trifluoromethyl)phenyl)acrylate (Table 18: Entry 2)

C8A14 December 201216:18

callum nmrs Page 1

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85

Figure 9.2.3: 1H NMR of methyl 3-(p-tolyl)acrylate (Table 18, Entry 5)

C9A14 December 201216:29

callum nmrs Page 1

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10. Bibliography

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retrieved from: http://www.forbes.com/sites/mindylubber/2012/12/17/fossil-

fuel-divestment-is-timely-issue-for-investors/

[2] Q. Sun, E. Vrieling, R. van Santen, N. Sommerdijk, Current Opinion in solid state and

materials science, 2004, 8, 111-120.

[3] R. Bates, Organic Synthesis using Transition Metals, John Wiley and Sons.

[4] N. Miyaura, A. Suzuki, J. Chem. Soc., Chem. Commun., 1979, 866-867.

[5] A. F. Little, C. Dai, G. C. Fu, J. Am. Chem. Soc., 2000, 122, 4020–4028.

[6] Y. Hatanaka, T. Hiyama ,The Journal of Organic Chemistry, 1988, 53, 918.

[7] J. Y. Lee, G. C. Fu, J. Am. Chem. Soc., 2003, 125, 5616-5617

[8] A. King, N. Okukado, E. Negishi, J. Chem. Soc., Chem. Commun., 1977, 683-684.

[9] J. Liu, Y. Deng, H. Wang, H. Zhang, G. Yu, B. Wu, H. Zhang, Q. Li, T. B. Marder, Z. Yang,

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