MScChemistry

ScienceforEnergy&Sustainability

MasterThesis

HeterobinuclearOrganometallicComplexes

AStudyoftheStructure,ElectronicBehaviourandReactivityofNewLow-Valent

Compounds

AnneSofieAbels

10000732

August2018

48ECTS

November2017–August2018

Supervisor/Examiner: Examiner: MScPascalJurt Prof.dr.HansjörgGrützmacher

Prof.dr.BasdeBruin

Dr.ChrisSlootweg

ETHZürich

DepartmentofChemistryandAppliedBiosciences

LaboratoryofInorganicChemistry

TheGrützmacherGroup

1

Acknowledgements

Firstofall,IwouldliketothankProf.Dr.HansjörgGrützmacherfortheopportunitytocarry

out my master thesis in his group. Second, I thank Prof. Dr. Bas de Bruin and Dr. Chris

Slootweg for being my second examiners. Then, a massive thanks goes to my daily

supervisorPascalforallhishelpinthelab,endlessexplanations,encouragingenthusiasmfor

chemistry, enjoyable times in and outside of the lab and of course for showing me the

beauty Switzerlandhas to offer. I am very grateful for the skills and knowledge youhave

taughtmethepastninemonths,whichultimatelyresulted inasuccessfulproject. Iwould

like to thankMatt andGrégoire for their helpwith theNMR experiments and Fabian for

helpingmewiththeXRDmeasurements.DongjunandJanusUrbanus,thankyouforthenice

atmosphereinthelabandLucjethanksforbeingmyNederlandserotsindebranding.Then,

IofcoursewouldliketothanktherestofallthemembersoftheGrützmachergroupforthe

greattimeIhadwiththem,youdefinitelymademystayinZürichunforgettable.Lastbutnot

leastIwouldliketothankmyfamilyandfriendsfortheirloveandsupport,andespeciallymy

parents,whoarealwaysthereformeandgavemetheopportunitytohavethisexperience

abroad.

2

Index

1.INTRODUCTION 4

2.RESULTSANDDISCUSSION 10

2.1SynthesisandCharacterisationoftheTropLigand:PhC≡CTropPPh2 10

2.2SynthesisandCharacterisationoftheRhodiumPhC≡CTropPPh2Dimer 12

2.3HeterobimetallicRh(I)Pt(II)Complexes 152.3.1SynthesisandXRDStudiesofHeterobimetallicRh(I)Pt(II)Complexes 152.3.2NMRStudies 252.3.4ThermogravimetricAnalysis 302.3.3PlatinumInfluence 30

2.4ReactivityofHeterobimetallicRh(I)Pt(II)Complexes 31

2.5HeterobimetallicComplexes–OtherGroup9Metals(Iridium&Cobalt) 37

3.CONCLUSION&OUTLOOK 39

4.EXPERIMENTALSECTION 41

5.APPENDIX 49

ListofAbbreviations 49

6.REFERENCES 50

3

Abstract

Six new heterobimetallic Rh(I)Pt(II) complexes supported by a novel type of chelating

tropPPh2 ligand were synthesised, characterised (figure 1) and tested in nitrous oxide

activation. Heterobinuclear complex 13 proved to be the most efficient homogeneous

catalystforthehydrogenationofthegreenhousegasN2Ouptodate(TON=430),producing

benignwaterandnitrogenundermildreactionconditions.Ligandalterationattherhodium

centre led to fundamental insight into the nature of the bimetallic core: NMR and XRD

studies revealed that cationic compounds contained a shorter metal-metal bond and

stronger 103Rh-195Pt coupling in NMR, while neutral complexes demonstrated a longer

intermetallicdistanceandweaker 1JRhPtcoupling.Furthermore,acorrelationbetween195Pt

satellites in 31P{1H} NMR and the intermetallic bond length was found. In these

heterobimetallic systems, the platinum centre appeared to serve as a supporting ligand,

donatingelectrondensitytotherhodium,whichissuggestedtobeessentialintherhodium

platinumbond.

Figure 1.Novel type of chelating tropPPh2 ligand that enables the coordination of rhodium(I) and

platinum(II). Ligand variation of the rhodium centre gave fundamental insight in the intermetallic

bond.

PPh2

Ph Ph

PPh2

Rh

Ph PhPt

L

+ -X10: L = Cl- 11: L = ACN, X = PF612: L = ACN, X = BArF

13: L = OTf-14: L = µ-Cl, X = BArF

15: L = µ-ClTlCl, X = BArF

8

4

1.Introduction

Nature is a great source of inspiration for the rational design of new catalysts. Since the

presenceofmultimetalliccentresinbiomoleculesarerecognisedtobeofvitalimportancein

enzymatic processes, bimetallic complexes are considered highly interesting for the

activationofdifferentinorganicandorganicsubstrates.[1]Aprominentexampleisagroupof

metalloenzymes that are involved in hydrogen reduction/water oxidation. These so-called

hydrogenasescanbecategoriseddependingontheirmetalactivesitesinmonometallic[Fe],

homobimetallic [FeFe] and heterobimetallic [NiFe] hydrogenases (figure 2). These

metalloenzymes,foundinvariousmicroorganisms,areresponsibleforprovidingenergyand

balancing the redox potential of a cell. In particular, the homobimetallic and

heterobimetallichydrogenasesaremoreactiveintheoxidationofhydrogenandgeneration

ofdihydrogen.[2]

Figure 2. Active site of a) monometallic [Fe] hydrogenase model b) homobimetallic [FeFe]

hydrogenaseandc)heterobimetallic[NiFe]hydrogenase.

Also, in synthetic chemistry there are well-known bimetallic catalysts that show the

importance of catalytic systems containingmetal-metal bonds. The study of intermetallic

bonds has been of great interest for many researchers over half a century,[3] with the

descriptionof the firstmultiplemetal-metalbondsbyProf.F.AlbertCotton in1964.[4]His

work contributed a great deal to the understanding of intermetallic interactions.[5,6]

Although numerous binuclear compounds are described in literature, the catalytic

application of these complexes is not well documented.[7–14] A renowned example of a

bimetalliccatalystistherhodium(II)acetatedimerdiscoveredinthe70’sthatisutilisedasa

carbeneandnitrenetransfercatalystandissuperiortomononuclearanaloguesintermsof

functional group tolerance and catalyst loading (figure 3).[3] Lately, a renewed interest in

Ni Fe

SSCysCys

X

CNCOCN

S

S

Cys

Cys

X: O2-, OH-, OH2, SO, in the reduced form X: H-)

Fe

S

S

N N

COOC Fe Fe

SS

CO

COCN

SCys

OCNC

4Fe-4SNH

a) b) c)

5

bimetallicsystemsresultedintheuseofmetal-metalbondedcompoundsinvariouscatalytic

applications[15]suchashydrogenationreactions[16],smallmoleculeactivation[17,18],coupling

reactions[19]anddiazo-freecyclopropanation.[20]

Figure 3. Schematic representation of rhodium(II) acetate dimer. This dimer is known for carbene

and nitrene transfer reaction and is thought to be one of themost potent catalysts containing a

metal-metalbond.

Thesynthesisandapplicationofhomobimetalliccomplexesaremoreestablishedthan the

preparation of heterobinuclear species, as these compounds, where two different metal

centres are combined within the molecule, are often more challenging to prepare.[21]

Nevertheless the study to heterobimetallic catalysts remains interesting, since the

combinationof twodifferentmetalcentreshasprovento lead tounprecedentedcatalytic

transformations and activities.[8] Most of these heteronuclear transitionmetal complexes

incorporate an early and a late transition metal, bridged by a ligand framework. The

intermetallic bond in these heterobimetallic complexes can be described as a dative

interactionbetweenahard,Lewisacidicearlytransitionmetalormaingroupelementanda

softLewisbasiclatetransitionmetal.[22]ThegroupofLurecentlydescribedaseriesofearly

transition metal-cobalt heterobimetallic complexes capable of nitrogen activation at the

cobaltcentre.Theearly-latemetalsetissupportedbyaheptadentateligandwithchelating

phosphorusandnitrogendonoratoms(figure4).[23]

RhRh

O

O

O

O

OO

OO

6

Figure 4. Structureofearly-lateheterobimetallic complexwhereaheptadentate ligand,containing

phosphorusandnitrogendonoratoms,enforcesthedinuclearM-M’axis.

The intermetallic interaction and the catalytic application of heterobinuclear complexes

bearing two late transitionmetals remain ratherunderexplored.Still, this fieldhasbeena

subjectofsignificantresearchinterest.Forexample,thegroupofChensynthesiseslate-late

heterobimetallic Pd/M (M: Cu, Ag, Au) and Pd(II)/Zn(II) model systems to gain detailed

mechanistic informationon transmetalation reactions inSonogashiraandNegishi coupling

reactions, respectively.[24,25] Furthermore, Nocera and co-workers described a

heterobimetallic complex with a Rh(II)Pt(I) core which is readily oxidised to a Pt(III)Rh(II)

core. Irradiation of the oxidised product promotes the photoelimination of halogen and

regenerates the reducedRh(II)Pt(I) core.Halogen oxidation and halogen photoelimination

chemistry isconsideredpromising for theproductionofdihydrogen fromHXsubstrates to

store solar energy.[26] Additionally, Mankad et al. recently studied a heterobimetallic

ruthenium-silvercompoundforhydrogenactivationandthecatalyticsemi-hydrogenationof

alkynes(figure5).[27]

Figure 5. A ruthenium-silver heterobimetallic complex for the catalytic semi-hydrogenation of

alkynes.

NN

M

P CoPiPr2

NN

PiPr2iPr2

M = V, Cr

N

N

RRH

R

HR

H2 (1atm)Ag-Ru cat. (20%)

xylenes,150 ºC, 24h

N

NAg Ru

COCO

7

Duringthiscatalysisthemetal-metalbondiscleaved,leadingtotwomonometallicspecies.

Toclosethecatalyticcyclethesilverrutheniumbondmustberestored,whichlikelycaused

the high catalyst loading (20%). However, bimetallic cooperation led to the observed cis

selectivity, which only was observed in very few monometallic systems before.[28,29] This

phenomenon of fragmentation during catalysis is common in bimetallic catalysis, since

metal-metalbondsareoftenmorelabilethanorganicbonds.[30]Liganddesigncanbeatool

toavoidbreakingtheintermetallicbondbycreatingasystemthatallowsthecoordinationof

two different metal centres in close proximity, assisting a metal-metal interaction that

remainsintactthroughoutacompletecatalyticcycle.

Inthiscurrentstudy,anewtypeofligandwasdesignedwhichenablesthecoordinationof

two different late transition metals. The newly designed chelating ligand features a trop

(trop = 5-dibenzosuberene) unit, which contains a seven-membered ring, providing the

preparation of robust complexes. A chelating concavely shaped tropPPh2 ligand can be

prepared binding a σ-donor diphenylphosphine to the trop unit, which itself bears a

sterically encumbered double bond that functions as a π-accepting coordination site.[31]

PreviousworkoftheGrützmachergroupshowedthatthisligandallowsstrongcoordination

todifferentlatetransitionmetals,suchasrhodium,palladiumandiridium,andisespecially

valuable for stabilizing low-valent oxidation states.[32–35] Further studies on this tropPPh2

ligandresultedinthedevelopmentofaligand,TMSC≡CTropPPh2,thatisabletocoordinateto

two electron rich group 9 and 10 d8-metals, while leaving open coordination sites at the

metalcentres.Whereasthefirstmetalisboundtothetropmoietyviainteractionwiththe

phosphineandalkene,thesecondmetaliscoordinatedtothealkynemoieties(figure6).[36]

Figure 6. Previous work of the Grützmacher group, where the specially designed TMSC≡CTropPPh2

ligandallowsthecoordinationoftwodifferentlatetransitionmetalsinachelatingfashion.

PPh2

TMS TMS

PPh2

M1Ln

TMS TMSM2Ln

n+Ph2P

TMSTMS

=

M1, M2: Late Transition Metals (group 9 & 10)Ln: Me, Cl, ACN, OTf

8

Inthesynthesisofthisnoveltypeofchelatingligandthealkynegroupswereintroducedbya

cross-coupling Sonogashira reaction. This product required purification by column

chromatography, which involved the use of large amounts of solvents and could not be

scaledupsuccessfully.The last step in this synthesis, the substitutionofa chlorideby the

diphenylphosphine,wasrathertedious,sincedeprotectionofthetrimethylsilyl(TMS)group

canoccurbystronglybasicorproticreactantsorsolvents.Fromligand1asyntheticrouteto

heterobimetallicRh(I)Pt(II)complexeswasdeveloped(figure7).[36]Thesynthesisof2posed

problems, as the isolation and purification required a fine tuned, non-trivial reaction

protocolandpurificationstep.

Figure 7. Previous work of the Grützmacher group: synthesis of heterobimetallic Rh(I)Pt(II)

complexes3and4basedontheTMSC≡CTropPPh2ligand1.

Heterogeneous rhodium-platinum carbonyl catalysts have proven to be active in

hydrogenation reactions of aromatic compounds and CO. In toluene hydrogenation to

methylcyclohexane the presence of platinum appeared to improve the activity of the

catalyst.Howeverbothcatalystsdecomposedafterafewruns.[37]ThehydrogenationofCO

yieldedethyleneglycolandmethanolthatsuggestedthatmixedmetalclusters,whichcould

notbedetermined,wereinvolvedinthecatalyticreactions.[38]

PPh2

TMS TMS

PPh2

Rh

TMSPh2P

Rh

TMSTMS

ClCl

TMS

PPh2

Rh

TMS TMSPt

ClPPh2

Rh

TMS TMSPt

N

+ -PF6

[Rh(C2H4)2Cl]2

DCM

TlPF6

DCM/ACN

[Me2Pt(SMe2)]2, DCM

1 2

4 3

9

The goal of this study was to synthesise a similar chelating trop ligand, allowing the

coordinationoftwodifferentlatetransitionmetals,whileavoidingthepreviouslydescribed

problems.Furthermore, thepreparationofdifferentheterobimetalliccomplexes,basedon

thenewligand,werestudied,usingd8metalsrhodium(I)attheM1positionandplatinum(II)

as M2 (figure 6). Additionally, the coordination of other group 9 metals, iridium(I) and

cobalt(I),tothechelatingtropligandwasinvestigated.Also,theinfluenceofvariousligands

coordinated to theM1metal centre on themetal-metal bondwas explored. Studying the

structureandelectronicpropertiesofthesedifferentheterobinuclearcomplexescouldgive

fundamentalinsightinthisunderdevelopedlatemetal-metalbond.Finally,thereactivityof

this classof compounds towards theactivationof thegreenhousegasnitrousoxide (N2O)

withhydrogenwasstudied.

10

2.ResultsandDiscussion

2.1SynthesisandCharacterisationoftheTropLigand:PhC≡CTropPPh2

Based upon the synthesis of ligand 1 that was described in unpublished results of the

Grützmachergroup,anexperimentalprocedureforthepreparationofanewchelatingtrop

ligand 8 was developed (figure 8).[36] In this new ligand, the TMS groups on the alkyne

moiety were replaced by phenyl groups. First, a Sonogashira coupling was performed to

introducephenylacetyleneinthetropmoietyandbynucleophilicsubstitutionusingthionyl

chloridetheOHgroupisreplacedbyachloride,formingcompound7.Forthelaststepofthe

ligand synthesis, the substitution of the chloride by the phosphine, a different procedure

was applied and optimised to obtain the final product. Diphenylphospine was added to

compound 7 and the reactionmixturewas stirred at 50°Cwhile forming a precipitate of

chlorodiphenylphosphonium salt.UponadditionofNa2CO3 as a base,HClwas eliminated,

leadingtoproduct8witha63%yield.Thisstepdeviates fromthe ligandsynthesisof the

TMS analogue, where n-butyllitihium was used as reagent to deprotonate

diphenylphosphine. The in situ formed lithium diphenylphosphine then replaced the

chloride.However,deprotonationoftheTMSgroupscouldoccurduringthisstep.Theyield

of the synthesis of the PhC≡CTropPPh2 ligand 8was comparable to the TMS analogue and

upscaleofthereactionwaspossible.Therefore,thepreparationofthePhC≡CTropPPh2ligand

wasshowntobemorereliableandscalablecomparedtotheTMSC≡CTropPPh2ligand.Infigure

9 thecrystal structureof thechelating ligand8 isdepicted.This liganddesignenables the

anchoring of twometals using a set of different chelating ligands: phosphine, alkene and

alkynes.

11

Figure8.Three-stepsynthesisof ligand8, includingaSonogashiracouplingto introducethealkyne

moieties in themolecule,yielding6.This is followedbysubstitutionof thealcoholby thechloride

andthefinalproduct8isobtainedbythereactionof7withdiphenylphosphine.

Figure 9.Molecular structureof8.Hydrogenatomsand solventmolecules areomitted for clarity.

Selectedbonddistances(Å):C1-P1:1.890(3),C2=C3:1.373(5),C4≡C5:1.207(5),C6≡C7:1.201(5).

Ph2P

PhPh

HO

PhPh

Br Br

HO

Cl

PhPh

=

PPh2

Ph Ph

PhCCH

5 % Pd0, 5% CuI

Tol/Et3N

HPPh2Na2CO3 (aq)

Tol/n-Hex50ºC, 3 days

SOCl2, pyridineDCM

Yield: 63%

5 6

78

C2

C3P1

C1

C4

C5

C6

C7

12

2.2SynthesisandCharacterisationoftheRhodiumPhC≡CTropPPh2Dimer

Complex 9 was synthesised by reacting ligand 8 with [Rh(C2H4)2Cl]2 in benzene at room

temperature(figure10).Clean9precipitatedfromthereactionmixtureasaredpowderin

good yield. The synthesis of 9 is considerably more convenient compared to theTMSC≡CTropPPh2 trop dimer,where isolation and purification of the product is tedious and

non-scalable.Singlecrystalsofcomplex9wereobtainedbyslowdiffusionofn-hexaneinto

solution of 9 in dichloromethane and analysed by X-ray diffraction. The structure of this

complexisshowninfigure11.Backdonationfromthemetalintotheπ*orbitaloftheolefins

leads to weakening and elongation of the double bond (1.470(3) Å in 9, compared to

1.373(5)Åinfreeligand8).

Figure10.Synthesisofcomplex9fromligand8with[Rh(C2H4)2Cl]2.

Figure11.Molecularstructureof9.Hydrogenatomsandsolventmoleculesareomittedforclarity.

Selectedbonddistances[Å]andangles[°],centroidofC2=C3isindicatedasct1andct1’iscentroid

ofC2’=C3’:Rh1/1’-ct1/1’:2.009(2),Rh1/1’-P1/1’:2.169(6),C2/2’=C3/3’:1.470(3),Rh1-Cl1:2.375(6),

Rh1-Cl1’:2.507(6),ct1-Rh1-P1:92.013(6),ct1-Rh1-Cl1’:100.008(6)Cl1’-Rh1-Cl1:80.76(2)Cl1-Rh1-P1:

87.94(2).

8

[Rh(C2H4)2Cl]2

BenzeneRT, 1 hr

PPh2

Rh

PhPh2P

Rh

PhPh

ClCl

Ph 9

PPh2

Ph Ph

Yield: 79%

Cl1

Rh1

P1

C2C3

C1

Cl1’

Rh1’

P1’

C2’C3’

13

In 1H NMR and 31P NMR spectra of complex 9 broad signals were observed at room

temperature. Line broadening in NMR can be caused by several factors, such as fast

relaxationofthemolecule,thepresenceofaparamagneticspeciesandchemicalexchange.

Cooling and heating experiments of the NMR sample indicated that there is indeed a

dynamicprocess,whichcauses the linebroadening in theNMRspectra.When there isan

equilibriumbetweentwospeciescoolingthesamplecanslowdowntheexchangeandatthe

low-temperaturelimitastaticspectrumcanbeobserved.Heatingthesampleincreasesthe

rateofexchange,whichatthehigh-temperaturelimitleadstothefullyaveragedspectrum.

Betweenthesetwoextremesbroadsignalsareobserved[39].Variabletemperature1HNMR

and 31P NMR spectra from 248 K to 378 K in 1,1,2,2-tetrachloroethane-d2were recorded

(figure12).1HNMRiszoomedinonthesignalofthebenzylicproton.

Figure12revealedthatcompound9waspresentastwospeciesinequilibriuminsolution,

withdifferentRh-Pcouplingsof260Hzand194Hz.NMRstudiesinacoordinatingsolvent,

ACN-d3, resulted in cleavage of the dimer and coordination of the acetonitrile to the

rhodium. Sharp signals were recorded, indicating that there was no chemical exchange.

Basedontheseresultsitisproposedthatthereisanequilibriumbetweenthecis-andtrans-

isomer(figure13).

14

Figure 12. a) Variable temperature 1H NMR and b) 31P NMR of 9 in 1,1,2,2-tetrachloroethane-d2

reveals an equilibrium in chlorinated solvents. Shimming was not carried out before every

experiment,which resulted in broadeningof the signals in someof the experiments. The 1HNMR

spectraarezoomedinonsignalofthebenzylicproton.

4.54.64.74.84.95.0f1 (ppm)

378 K

368 K

358 K

348 K

338 K

328 K

318 K

308 K

298 K

288 K

278 K

268 K

258 K

248 K

a)

102104106108110112114116f1 (ppm)

378 K

368 K

358 K

348 K

338 K

328 K

318 K

308 K

298 K

288 K

278 K

268 K

258 K

248 K

b)

15

Figure13.Equilibriumbetweentrans-isomer9andcis-isomer9ainchlorinatedsolventsledtobroad

signalsinNMRatroomtemperature.

2.3HeterobimetallicRh(I)Pt(II)Complexes

Complex 9 was used as building block for the synthesis of the heterobimetallic species

studied in this thesis. Here we describe the preparation and analysis of these dinuclear

Rh(I)Pt(II)compoundswillbedescribed.

2.3.1SynthesisandXRDStudiesofHeterobimetallicRh(I)Pt(II)Complexes

Thesecondmetal,platinum(II),wasintroducedbyreactingcomplex9with[Me2Pt(μ-SMe2)]2

in dichloromethane to produce complex10. In a one-pot synthesis, complexes11 and12

werepreparedfrom9byabstractingthechloridewithTlPF6orNaBArF,respectively(figure

14).Thissaltmetathesisreactionwascarriedoutinthepresenceofacetonitrile,leadingto

thecoordinationofacetonitriletotherhodiumcentre,withnoncoordinatinganionsPF6and

BArFascounterions.

PPh2

Rh

PhPh2P

Rh

PhPh

ClCl

Ph 9 9a

PPh2

Rh

Ph

Ph2P

Rh

PhPh

ClCl

Ph

16

Figure 14. Synthesis of PhC≡CTropPPh2 heterobimetallic Rh(I)Pt(II) complexes 10, 11 and 12 fromPhC≡CTropPPh2dimer9and[Me2Pt(SMe)]2.

Figure 15. a) Molecular structure of 10. b) Molecular structure of 11 and 12. Hydrogen atoms,

counterionsandsolventmoleculesareomittedforclarity.

PPh2

Rh

Ph PhPt

N

+ -PF6

TlPF6, DCM/ACN NaBArF, DCM/ACN

PPh2

Rh

Ph PhPt

N

+ -BArF

[Me2Pt(SMe2)]2, DCM

PPh2

Rh

Ph PhPt

Cl

PPh2

Rh

PhPh2P

Rh

PhPh

ClCl

Ph

Yield: 58%Yield: 63%

Yield: 85%

9

10

11 12

Rh1 N1

P1

Pt1C7

C8

b)

Rh1

Pt1

P1

C7

C8

Cl1

a)

C1

C2C3

C4

C5

C6

C1

C2

C3

C4

C5

C6

C9

C9

17

Table1.Selectedbonddistances[Å]andangles[°]for10,11and12,wherethecentroidofC2=C3is

indicatedasct1,ct2forC4≡C5andct3forC6≡C7.

Compound 10 11 12

Rh1-ct1 1.953(3) 1.979(3) 1.978(5)

Rh1-P1 2.1850(8) 2.2055(9) 2.1904(12)

C2=C3 1.471(4) 1.467(5) 1.454(6)

Rh1-Cl1/N1 2.3294(7) 2.059(3) 2.02(3)

Rh1-Pt1 2.7657(2) 2.6784(3) 2.6979(4)

C4≡C5 1.227(4) 1.217(5) 1.226(7)

C6≡C7 1.228(4) 1.220(5) 1.225(7)

Pt1-ct2 2.233(3) 2.257(3) 2.272(5)

Pt1-ct3 2.215(3) 2.266(3) 2.247(6)

P1-Rh1-ct1 93.167(8) 93.303(9) 93.524(13)

ct1-Rh1-Pt1 75.701(8) 77.730(10) 77.853(12)

Pt1-Rh1-Cl1/N1 96.34(2) 91.59(8) 92.4(2)

Cl1/N1-Rh1-P1 94.86(3) 97.39(9) 96.1(7)

ct2-Pt1-C8 92.556(12) 94.381(14) 91.708(2)

ct3-Pt1-C9 94.427(11) 93.314(14) 94.128(2)

ct2-Pt1-ct3 93.889(10) 94.747(12) 91.740(18)

C8-Pt1-C9 86.87(13) 87.04(15) 85.9(3)

Rh1-Pt1-ct2 79.832(10) 80.254(9) 79.746(12)

Rh1-Pt1-ct3 78.966(10) 79.815(9) 76.975(12)

Rh1-Pt1-C8 99.80(9) 99.77(11) 101.06(17)

Rh1-Pt1-C9 97.14(9) 98.41(11) 99.69(17)

Thegeometryof10-12canbedescribedasasquareplanargeometryaroundtherhodium

centre, while the geometry around the platinummetal centre can be defined as square

pyramidal,where the rhodium centre occupies the axial position of the square pyramidal

structure(figure15andtable1).Thesignificantlyelongatedolefinbondfor10(1.471(4)Å),

11 (1.467(5)Å)and12 (1.454(6)Å) indicatesstrongbackdonationfromthemetalintothe

anti-bondingorbitalsπ*of theC=Cdoublebond.TheRh-Ptbond is considerably longer in

complex 10 (2.7657(2) Å) than in complexes 11 (2.6784(3) Å) and 12 (2.6979(4) Å).

18

Furthermore,theRh-Cl(2.3294(7)Å)bondissubstantiallylongerthantheRh-N(2.059(3)Å

and 2.02(3) Å) bond. Although the differences in the olefin bond length are rather small

betweencomplexes10-12,itisobservedthatthestrongerπ-donorchlorideresultsinmore

backdonationtoC=Colefintropanti-bondingorbitals,whichindicatesamoreelectronrich

rhodium centre. This interaction can be described as a “push-pull” interaction,where the

olefinacceptselectrondensityintotheπ*anti-orbitaltoreducetheelectrondensityonthe

metal(“pull”).Thisreducesthedestabilisationgeneratedbytheπdonationofthechloride

tothemetal(“push”).Thispush-pullmechanismisknownforsquareplanard8complexes.[40]

Since compounds11 and12 are cationic,while10 is neutral, it is expected that all bond

lengths are shortened in the cationic complexes. This is because the positive charge will

decreaseall orbital energies resulting inbetteroverlapbetween the ligandand themetal

orbitals. Remarkably, this is not observed for the Rh-ct1, whichmay be explained by the

push-pull effect of the chloride compared to the acetonitrile that is solely a σ-donor.

However, the influenceof thepositive charge is strongly reflected in theRh-Pt bond that

indeedbecomesmuchshorterincations11and12comparedtoneutral10.

Furthermore,NMRandcrystallographydataoftheacetonitrileboundcomplexes11and12

wereverysimilartooneanother,whichindicatesthatthecounteriondoesnotinfluencethe

electronicbehaviourandgeometricalfeaturesofthecomplexes.However,BArFconsiderably

increasesthesolubilityofthecomplexinnon-coordinatingsolventscomparedtocompound

11. Furthermore, the use of toxic thallium(I) is avoided in the synthesis of complex 12.

Thereforethesynthesisanduseofcomplex12ismorepreferredcomparedto11.

Consequently, silver triflate was used to abstract the chloride from 10 to bind a weakly

coordinatinganionictriflate,totherhodiumcentre,leadingtocomplex13 (figure16).XRD

studiesrevealedthatthegeometryofcomplex13canbedescribedassquareplanararound

therhodiumcentreandsquarepyramidalaroundtheplatinum(figure17andtable2).The

C=Colefintropbondiselongatedinasimilarfashionasinchloridecomplex10duetoπback

donation (1.473(7)Å in13, 1.471(4)Å in10).Also, themeasuredmetal-metalbondof13

(2.7427(4)Å)israthercomparabletotheRh-Ptbondof10(2.7657(2)Å).Thisdemonstrates

the similar electronic properties for both neutral complexes. Moreover, the metal-metal

bondlengthof13islongerthantheacetonitrilecoordinatedcomplexes11(2.6784(3)Å)and

19

12 (2.6979(4) Å), indicating as well that a neutral complex results in an elongated Rh-Pt

bond.

Figure16.Synthesisofcomplex13from10withAgOTf.

Figure17.Molecularstructureof13.Hydrogenatomsandsolventmoleculesareomittedforclarity.

PPh2

Rh

Ph PhPt

Cl AgOTf

THF

PPh2

Rh

Ph PhPt

OTf

Yield: 69%10 13

P1

Rh1

Pt1

C2

C3

C1

C4

C5

C6

C7

O1

20

Table2.Selectedbonddistances[Å]andbondangles[°]of10and13,wherethecentroidofC2=C3is

indicatedasct1,ct2forC4≡C5andct3forC6≡C7.

Compound 10 13

Rh1-ct1 1.953(3) 1.954(5)

Rh1-P1 2.1850(8) 2.1964(14)

C2=C3 1.471(4) 1.473(7)

Rh1-Cl1/O1 2.3294(7) 2.087(4)

Rh1-Pt1 2.7657(2) 2.7427(4)

C4≡C5 1.227(4) 1.231(7)

C6≡C7 1.228(4) 1.217(8)

Pt1-ct2 2.233(3) 2.235(5)

Pt1-ct3 2.215(3) 2.266(5)

P1-Rh1-ct1 93.167(8) 93.133(14)

ct1-Rh1-Pt1 75.701(8) 76.964(14)

Pt1-Rh1-Cl1/O1 96.34(2) 89.87(10)

Cl1/N1-Rh1-P1 94.86(3) 100.04(11)

ct2-Pt1-C8 92.556(12) 94.085(2)

ct3-Pt1-C9 94.427(11) 91.781(2)

ct2-Pt1-ct3 93.889(10) 91.040(18)

C8-Pt1-C9 86.87(13) 85.1(2)

Rh1-Pt-ct2 79.832(10) 77.785(13)

Rh1-Pt1-ct3 78.966(10) 78.050(14)

Rh1-Pt1-C8 99.80(9) 100.50(16)

Rh1-Pt1-C9 97.14(9) 100.16(15)

Then, the preparation of a T-shaped rhodium complex, with a non-coordinating anion,

leadingtoopencoordinationsitecistotheM-M’bondwasattempted(figure18).SuchaT-

shaped bimetallic complexes is expected to show enhanced reactivity due to the readily

availableopencoordinationsite,asisdescribedformonometallicRh(I)analogues.[41]

21

Figure18.AttemptedpreparationofT-shapedrhodiumcomplexwithanopencoordinationsitecisto

theRh-Ptaxis.NaBArFandTlBArFwereusedaschloridescavengers.

Thereactionof10withNaBArFintoluenedidnotresultinaT-shapedrhodium,butonlyone

chloridecouldbeabstractedanddimerisationofthecomplexwasobserved,leadingto14.

When using TlBArF, another chloride scavenger, to remove the chloride bridged chloride-

thallium-chloride 15 complex was formed (figure 19). This indicated that the chloride is

stronglycoordinatedtotherhodiumcentre.Singlecrystalsof14and15wereanalysedby

XRD (figure 20). These dimeric structures can be as well described as square planar d8

aroundrhodiumandsquarepyramidalfortheplatinumcentre(table3).

Figure19.Synthesisofdimericcomplexes14and15from10,usingdifferentBArFsaltsinattemptto

abstract thechloride from the rhodiumcentre. For15 noyield is reported, since the reactionwas

onlyperformedattestreactionscale.

PPh2

Rh

Ph PhPt

Cl

10

Na/Tl BArF

Toluene

PPh2

Rh

Ph PhPt

NaBArF, Toluene TlBArF, Benzene

PPh2

Rh

Ph PhPt

Cl

PPh2

Rh

Ph PhPt

P

Rh

PhPhPt

Cl

+ -BArFPh2 PPh2

Rh

Ph PhPt

P

Rh

PhPhPt

+ -BArFPh2

Cl ClTl

10

14 15Yield: 38%

22

Figure20.a)Molecularstructureof14.b)Molecularstructureof15.Hydrogenatoms,counterions

andsolventmoleculesareomittedforclarity.

P1

Rh1

Pt1C9

C8

C5

C4

C2C3

C6

C7

C1

Cl1

Pt2

Rh2

P2

a)

Rh1

Pt1

P1

C3

C4

C1

Cl1

Tl1Cl2

Rh2

Pt2

P2

b)

23

Table3.Selectedbonddistances[Å]andbondangles[°]forterminalchloride10,14and15,where

thecentroidofC2=C3isindicatedasct1,ct2forC4≡C5andct3forC6≡C7.

Compound 10 14 15

Rh1-C2=C3 1.953(3) 1.958(5) 1.964(4)

Rh1-P1 2.1850(8) 2.178(13) 2.183(11)

C2=C3 1.471(4) 1.456(7) 1.460(4)

Rh1-Cl1 2.3294(7) 2.403(11) 2.340(10)

Rh1-Pt1 2.7657(2) 2.788(4) 2.750(3)

C4-C5 1.227(4) 1.233(8) 1.227(6)

C6-C7 1.228(4) 1.212(8) 1.225(6)

Pt1-C4-C5 2.233(3) 2.217(6) 2.241(4)

Pt1-C6-C7 2.215(3) 2.256(6) 2.245(4)

P1-Rh1-ct1 93.167(8) 92.933(14) 94.079(11)

ct1-Rh1-Pt1 75.701(8) 76.049(13) 76.140(11)

Pt1-Rh1-Cl1 96.34(2) 97.60(3) 97.60(3)

Cl1-Rh1-P1 94.86(3) 92.85(4) 92.15(4)

ct2-Pt1-C8 92.556(12) 92.847(2) 93.439(19)

ct3-Pt1-C9 94.427(11) 92.816(2) 93.459(18)

ct2-Pt1-ct3 93.889(10) 91.042(18) 92.685(15)

C8-Pt1-C9 86.87(13) 85.5(2) 85.8(2)

Rh1-Pt-C4C5 79.832(10) 76.798(13) 79.407(11)

Rh1-Pt1-C6C7 78.966(10) 79.123(14) 79.066(11)

Rh1-Pt1-C8 99.80(9) 97.816(13) 98.605(14)

Rh1-Pt1-C9 97.14(9) 104.653(16) 99.161(13)

Comparison of bridged compound 15 and terminal chloride complex 10 revealed that 15

matched the trend in the electronic behaviour established previously, inwhich a cationic

compound led to a shorter intermetallic bond. However, 15 can be considered an

intermediate case, since the cationic charge is divided over two bridged molecules.

Therefore,themetal-metalbond isonlyslightlyshorter in15 (2.750(3)Å)comparedto10

(2.7657(2)Å).Sincethesamechlorideorbital isresponsibleforπdonationtotherhodium

centreandσdonationtothethalliumcentrein15,thereislesselectrondensitypresenton

24

therhodiumcentre,resultinginlessbackdonationandashorterolefinbond(1.460(4)Åin

15 compared to 1.471(4) in10). In14 theπ donationof the chloride is dividedonto two

metalcentres,whichwasdemonstratedinacomparableolefinbondlengthas15(1.456(7)

Å).However, theRh-Ptbondwas considerably longer in cationic complex14 (2.788(4)Å),

whichdidnotfittheelectronictrend.Therefore,thiselongatedintermetallicinteractionwas

explainedasastericeffectuptoformationofthedimer.

A survey of the CCDC crystallographic database 1 concerning all reported Rh-Pt bond

distances (214 rhodium-platinumbonds) reveals that themeasuredRh-Pt bond lengths in

this study (2.698 Å – 2.788 Å) are in range with described data in literature. Figure 22a

displays an example of a similar rhodium-platinum heterobimetallic compound with an

intermetallicbonddistanceof2.750(1)Å.[42]Thisreportedvalueiscomparablewiththedata

foundinthisstudy.AnothersimilarheterobimetallicRh-Ptcomplexreportedalongermetal-

metal bond distance (2.949(2) Å) that is explained due to the bridging hydride (figure

22b).[43]

Figure21.PlotofthesurveyresultoftheCCDCcrystallographydatabaseregardingallreportedRh-Pt

bond lengths in Å (X-axis). The Y-axis represents the number of structures for the given bond

distances.TherangeofmeasuredRh-Ptbonddistancesinthisstudyisindicatedinred.

1CSDConquest2018version5.39,accessed14August2018.

25

Figure22.a)HeterobimetalliccomplexwithaRh-Ptbonddistanceof2.750(1)Åb)heterobimetallic

compoundwithaRh-Ptbondlengthof2.949(2)Å.

2.3.2NMRStudies

Figure23.Synthesisedligand8,rhodiumdimer9andheterobimetallicRh(I)Pt(II)complexes10-15.

Table4summarisesselected1HNMRdatafortheligand8,rhodiumdimerprecursor9and

theheterobimetalliccomplexes10-15,thataredisplayedinfigure23.Thebenzylicprotonis

a distinctive feature of this trop system.Up to coordination to a rhodium centre the 2JPH

couplinggetsstronger.Additionally,theprotonsofthemethylgroupsontheplatinumare

observedasasingletaround1.29-1.46ppm,showingthecharacteristic195Ptsatellites.NMR

spectraofcompound14and15showedbroadsignals.Sincethesearedimericstructuresas

well, this could indicate a chemical exchange. The samples were cooled down, which

resulted in a static spectra where two species were observed, demonstrating indeed a

dynamic process.Moreover, sharp signals were observed when NMR spectra of 14 were

recorded in ACN-d3, therefore it was assumed that an equilibrium between the cis- and

Pt RhCO

CO

COCp

F

FF

F

F

F

F F

F

F

a)

Pt RhSi

Ph Ph

H

Si

Me3PPMe3

PMe3

PMe3

Ph

Ph

Cl

b)

H

PPh2

Ph Ph

8

PPh2

Rh

PhPh2P

Rh

PhPh

ClCl

Ph9

PPh2

Rh

Ph PhPt

N

+ -PF6 PPh2

Rh

Ph PhPt

N

+ -BArFPPh2

Rh

Ph PhPt

Cl

10 11 12

PPh2

Rh

Ph PhPt

P

Rh

PhPhPt

Cl

+ -BArFPh2

PPh2

Rh

Ph PhPt

P

Rh

PhPhPt

+ -BArFPh2

Cl ClTl

14 15

PPh2

Rh

Ph PhPt

OTf

13

26

trans-isomer, as seen for 9 (vide supra, figure 13), is responsible for the observed broad

signals in NMRin case of 14 and 15. Although the uncoupled signal from the protons of

methyl groups on the platinumwas sharp, broad signals for the 195Pt satellites were still

observed.Thiscanbeexplainedby195Ptrelaxationeffectsonthemethyl1Hlineshapes.[44]

Therefore,accuratedeterminationofthe2JPtHofcompound14and15wasnotpossible.As

the 1H NMR data was not conclusive about the electronic behaviour of these

heterobimetalliccompounds, furtherNMRstudies including31P, 103Rhand195PtNMRwere

performedtogainmoreinsightintheelectronicbehaviourofthisbinuclearsystem.

Table4.Selected1HNMRspectroscopicdataofcompounds8-15indifferentdeuteratedsolvents.All

datawereobtainedat298Kunlessotherwisestated.

Compound Solvent δHbenzylic

(ppm)

2JPH(Hz)/2JRhH(Hz)

δPt(CH3)2

(ppm)

2JPtH(Hz)

8 CDCl3 4.70 5.7 - -

9 ACN-d3 5.10 14.9 - -

10 THF-d8 4.92 14.4 1.46 92.4

11 CD2Cl2 4.98 15.4/2.3 1.35 87.7

12 CD2Cl2 4.94 15.3/2.4 1.35 87.9

13 THF-d8 5.19 14.8/2.8 1.46 90.1

14[a] THF-d8 4.69 14.3/-[b] 1.42 -[b]

15 THF-d8 5.29 14.4/2.4 1.29 -[b][a]Measuredat193K[b]Broadsignal

In 31P{1H}NMRdata a large change in chemical shiftwas observed upon coordination of

rhodium to diphenylphosphine (table 5). The chemical shift range (88-93 ppm) is

characteristic for these rhodium tropPPh2 complexes.[34,45,46] Introduction of the platinum

didonlyleadtominorchangesofthechemicalshift.Since195PtisalsoanNMRactivenuclei

platinumsatelliteswith33.7%intensityofthe31P{1H}signalcouldbedetected.[44]NMRdata

showed that complexes11 and12have theweakestphosphorus-rhodiumcoupling (197.9

Hzforbothcompounds),whiletheJPPtisstronger(537.4Hzand537.9Hz,respectively).For

theothercomplexesappliedthatiftheJPRhcouplingisstronger,theJPPtisweaker.

27

Table5.Selected31P{1H}NMRspectroscopicdataofcompounds8-15.Chemicalshifts(δ)aregivenin

ppmandcouplingsconstants(J)inHz.

Compound Solvent δ(ppm) 1JPRh(Hz) 2JPPt(Hz)

8 CDCl3 -12.95 - -

9 ACN-d3 93.70 186.5 -

10 THF-d8 89.88 217.5 519.9

11 CD2Cl2 91.40 197.9 537.4

12 C6D6 91.26 197.9 537.9

13 THF-d8 91.60 211.8 519.0

14 THF-d8 88.76 215.6 505.7

15 THF-d8 90.12 218.9 513.6

Additionally,otherNMRactivenuclei,195Ptand103Rh,weremeasuredtostudytheelectronic

behaviouroftheheterobimetalliccomplexes(table6and7).Complex15wasnotstudiedby195Pt and 103Rh NMR, since there was no sufficient amount of compound produced to

measure195Ptand103RhNMRspectra.Especially195PtNMRgivesvaluableinformationabout

the Rh(I)-Pt(II) bond, since the coupling between these two nuclei can bemeasured. The195Pt spectrawereacquiredwith 1Hdecoupling, as this leads to less crowded spectra. For

compound10theweakestPt-Rhcouplingwasmeasured(83.4Hz),whereasforcompounds

11 and12 strongermetal-metal couplingsweredetermined (104.1Hz and109.1Hz). The1JRhPtcouplingforcompound14couldnotbedetected,becauseoffastrelaxationofthe195Pt

nuclei,whichleadstolinebroadening.Asdescribedintheliterature,arelevantcontribution

to the relaxation of heavy nuclei, such as 195Pt, is the chemical shift anisotropy (CSA)

mechanism.[44]Since195Pthasalargechemicalshiftrange,theCSAeffectislargeraswell.[47]

Potentially, this iswhy the 1JRhPtfor14 could not be observed. In literature, one reported1JRhPtof24Hzfora[PtRh5(CO)15]-clusterwasfound,whichisconsiderablyweakerthanthe

measured couplings here.[48] However, the cluster is hardly comparable to the bimetallic

complexespresentedhere,sinceoxidationstateandligandsphereareverydifferent.

28

Table6.195PtNMRspectroscopicdataofcomplex10-15,withexceptionof14.Chemicalshifts(δ)are

giveninppmandcouplingsconstants(J)inHz.

Compound Solvent δ(ppm) 1JPtP(Hz) 2JPtRh(Hz)

10 THF-d8 -3274 530.1 83.4

11 CD2Cl2 -3223 546.7 104.1

12 CD2Cl2 -3196 538.0 109.3

13 THF-d8 -3263 519.4 94.5

14 THF-d8 -3321 502.5 -[a]

[a]Broadsignal

Although103Rhhasanaturalabundanceof100%,directmeasuringof103RhNMRisdifficult,

sinceithasalow(negative)gyromagneticratio,31.8timessmallerthan1H.Therefore,103Rh

NMRisoftendetected indirectlybyheteronuclearcorrelation,where1H iscorrelatedwith103Rh,whichenhances the sensitivityof the rhodiumnucleus[49].Here, 103Rhwasdetected

usingheteronuclearmultiple-quantumcoherence(HMQC).Asforthedatafromthe31P{1H}

spectra,aweakerRh-Pcouplingfortheacetonitrileboundcomplexes11and12,compared

tocomplexes10,13and15,whereananionic ligand isboundtotherhodiumcentre,was

observed.

Table7. 103RhNMRspectroscopicdataofcomplex9-15,withexceptionof14.Chemicalshifts (δ)are

giveninppmandcouplingsconstants(J)inHz.

Compound Solvent δ(ppm) 1JRhP(Hz) 2JRhH(Hz)

9 CDCl3 -6926 237.2 13.5

10 THF-d8 -7045 215.2 13.8

11 CD2Cl2 -7207 196.2 15.0

12 CD2Cl2 -7304 200.3 15.2

13 THF-d8 -6737 210.6 14.6

14 THF-d8 -7491 209.1 14.9

In table 8 NMR and XRD data of the heterobimetallic Rh(I)Pt(II) complexes 10-15 were

compared. It was observed that a shorter metal-metal bond length corresponded to a

29

strongerJRhPtcoupling.Forexample,complexes11and12 includedtheshortestRh-Ptbond

length (2.678Åand2.698Å, respectively)and thestrongestRh-Ptcoupling (104.1Hzand

109.3Hz, respectively),whereasa longerM-M’bond lengthof2.766Åandaweaker JRhPt

coupling(83.4Hz)wasmeasuredfor10.Furthermore,the2JPPtmeasuredin31P{1H}NMRwas

related to the Rh-Pt bond lengths, where a shorter metal-metal bond correlated to a

stronger JPPt coupling (graph 1). Thus, information about the intermetallic distance could

alreadyberetrievedfromanaccessible31P{1H}spectrum.

Table8.SelectedXRDandNMRspectroscopicdataofcomplexes10-15.

Compound dRh-Pt(Å) 1JPtRh(Hz) 2JPPt(Hz)

10 2.766 83.4 519.9

11 2.678 104.1 537.4

12 2.698 109.3 537.9

13 2.743 94.5 519.0

14 2.788 - 505.7

15 2.750 - 513.6

Graph1.CorrelationbetweenP-Ptcoupling(2JPPtinHz)andRh-Ptbondlength(dRhPtinÅ).

y=-294x+1330R²=0.89

490

500

510

520

530

540

550

2.65 2.70 2.75 2.80 2.85

2 JPP

t(Hz

)

dRhPt(Å)

30

2.3.4ThermogravimetricAnalysis

Thermogravimetric analysis (TGA) of compound12 was conducted. Themass changewas

measuredoveraperiodoftime,whilechangingthetemperature.Fromtheseexperiments

moreinformationabouttheformationofaT-shapedrhodiumcompoundcouldberetrieved.

At 171°C there was amass loss of 41 g/mol detected, which corresponds to acetonitrile

(figure24).Afterwards,itwastestedtoremovetheacetonitrilethermallybyheatingatthis

temperature.However,thisledtodecompositionofthecompound.

Figure24.TGAofcomplex12.Bluecurve:thermogravimetry(%),greencurve:differentialscanning

calorimetry,DSC,(μV/mg),pinkcurve:quasimultipleiondetection,QMID,(A).At171°Camassloss

wasdetectedthroughadecreaseintheDSC,whichcorrelatedtothelossofacetonitriledetermined

withQMID.

2.3.3PlatinumInfluence

The coordination environment of the platinummetal was altered to study the electronic

effectoftheplatinumcentreontheintermetallicbond.Methylgroupsarestrongσdonors.

Created with NETZSCH Proteus software

-1.5

-1.0

-0.5

0.0

0.5

DSC /(µV/mg)

50

60

70

80

90

100

TG /%

50 100 150 200 250 300 350 400 450Temperature /°C

2

4

6

8

10

12

QMID *10-12 /A

Main 2018-07-30 16:34 User: abelsa

[1]

s:1, m:41 [2]

[1]

↓ exo

31

Thereforedonationof their electrondensity to theplatinumcentre results in an electron

richmetal.Here, themethyl groupson theplatinumwereprotonatedwith a strong acid,

trifluoroacetic acid to remove themethyl groups and investigate the influence of these σ

donors on the platinum centre (figure 25). In 31P{1H}NMR loss of platinumwas observed

uponprotonation,asthePtsatelliteswerelost,andultimatelycompletedecompositionof

the compound was observed. This could indicate that electron density on the platinum,

donated by the σ donor methyl groups, is essential for the rhodium-platinum bond, by

electrondonationfromtheplatinumtotherhodiumandsuggeststhattheplatinumactsas

aligandtotherhodiumcentre.

Figure25.Protonationofthemethylgroupsontheplatinumbytrifluoroaceticacidledtolossofthe

platinummetal.

2.4ReactivityofHeterobimetallicRh(I)Pt(II)Complexes

Nitrousoxide isagreenhousegaswithawarmingpotential that isabout300timesbigger

thanCO2.[50]Anthropogenicemissionsofnitrousoxide,mainlyduetolarge-scaleapplication

offertilizers,arecausinganincreaseofthelevelofN2Ointheatmosphere.[51]AlthoughN2O

is thermodynamically unstable it is kinetically inert,[52] which necessitates the use of a

catalyst to activate themolecule and convert it to harmlessmolecules. The conversionof

N2Ointonitrogenandwatercouldbeconsideredhighlyinterestingforreducingthenitrous

oxidelevelsinatmospherethatareinvolvedinclimatechangeandozonedepletion(figure

26).

PPh2

Rh

Ph PhPt

N

+ -BArF

F3C OH

O

C6D6

PPh2

Rh

Ph PhPt

N

+ -BArF

Me+ CH4

+ CF3COO-

12 12a

32

Figure26.Schematicoverviewofnitrousoxideemissionsintheatmosphere.Naturalemissionsare

responsiblefor64%ofthenitrousoxideemissions.30%isemittedduetodenitrificationofthesoil,

whereas6%isreleasedintheatmosphereduetoindustrialprocesses,suchasthesynthesisofadipic

acid and nitric acid. Nitrous oxide is a greenhouse gas and related to climate change and ozone

depletion.CatalyticconversionofN2Otoharmlessnitrogenandwatermoleculescould reduce the

levelsinatmosphere.–FigurereprintedwithpermissionfromProf.Gianetti,UniversityofArizona.

N2O isknowntobeaunreactiveandpoor ligand for transitionmetals.[53] InnatureN2O is

activated and reduced in a cooperative fashion to nitrogen by the enzyme nitrous oxide

reductaseata tetranuclear copper sitebinding toadjacent copper centres (figure27a).[54]

Also in a heterogeneous catalytic system, Cu-ZSM-5, N2O is activated by metal-metal

cooperationoftwoadjacentcoppersites(figure27b).[55,56]

Figure27.ActivationofN2Obya)tetranuclearcoppersiteinnitrousoxidereductaseandb)adjacent

coppersitesinCu-ZSM-5.

Cu CuCu Cu

SNHis

NHis NHis

NHisNHis

NHis

NHis

ONN

HNHis

HNLys

Cu CuON N

OSiOAl

OAl OSi

a) b)

33

The development of homogeneous catalytic systems for the hydrogenation of N2O is of

interest,sincethiscouldgivemechanisticunderstanding inthis reaction,which isvaluable

forrationalcatalyticdesign.Recently,Milsteinreportedahomogeneouslycatalysedreaction

of N2O with hydrogen by a PNP ruthenium complex (figure 28), using relatively high

pressures of the gasses, 3 bar ofN2O and 4 bar ofH2, to producewater andnitrogen.[57]

Furthermore, a rhodium(I) carbene complex featuring a trop system was described in

previous work of the Grützmacher group to perform dehydrogenation of alcohols with

nitrous oxide as a hydrogen acceptor.[58] To our knowledge, there is no bimetallic system

identifiedforthisreaction.

Figure 28.HydrogenationofnitrousoxidehomogeneouslycatalysedbyaPNPrutheniumcomplex,

generatingwaterandnitrogenunder3barN2Oand4barH2at65°Cfor48hours.ATONof417was

measuredbasedupontheformationofwater.

In this work the activity of the different Rh(I)Pt(II) complexes (10-14) was systematically

tested for this reaction (figure 29). A solution of the catalyst in benzene or THF was

pressurisedwithonebarN2Oandhydrogen.Afterstirringthereactionmixturefor22hours

atroomtemperature,theturnovernumber(TON)wasdeterminedby1HNMRspectrumof

the reaction solution using mesitylene as an internal standard (figure 30). The results of

theseexperimentsare listed in table9.Acontrolexperimentwithout thepresenceof the

catalystwasperformedandshowednoformationofH2O.

THF, 65º, 48 hTON up to 417

N2O + H23 bar 4 bar H2O + N2

RuN

P

PH

H

CO

P: P(iPr)2

34

Figure29.Thereactivitytowardsthehydrogenationofnitrousoxideissystematicallytestedforthe

synthesized heterobimetallic complexes 10-14 in different solvents at room temperature for 22

hours.

Figure30.1HNMRspectrumofreactionsolutionafterthehydrogenationofnitrousoxideby13.The

amountofH2OformedandtheTONcanbecalculated,usingmesityleneasaninternalstandard.

PPh2

Rh

Ph PhPt

L

+ -X

Solvent, RT, 22 h

N2O + H21 bar 1 bar H2O + N2

10: L = Cl- 11: L = ACN, X = PF612: L = ACN, X = BArF

13: L = OTf-14: L = µ-Cl, X = BArF

1.52.02.53.03.5f1 (ppm)

H2O

Mesitylene

THF THF

35

Table9. OverviewoftheTONsbasedontheamountofH2Oformedafterhydrogenationofnitrous

oxidewithcomplexes10-14indifferentsolvents.

Rh(I)Pt(II)catalyst Solvent TONbasedonH2O

10 THF 11

11 THF Noreaction

12 THF 11

12 Benzene 47

13 THF 62

14 Benzene 6

Compound11 was not able to perform the activation of N2Owith H2, since the complex

formedahighly reactivespeciesunderhydrogenatmosphere,which led to intramolecular

follow-up reactions.Ultimately this resulted indecompositionof thecompound.Since the

non-coordinating counterion BArF increased the solubility in non-coordinating solvents

considerably,thecatalysisreactionsusingcomplexes12and14wereperformedinbenzene.

Thisenhancedthereactivityofthecatalyst12andaTONof54wasobtained.Furthermore,

a side reactionwas observed for12 and14 in benzene,whichwas the hydrogenation of

benzene to cyclohexane. A TON of 9 was calculated for 12 and 14 for 14. This reaction

seemed to compete with the hydrogenation of nitrous oxide and is quite remarkable,

considering the fact that very mild reaction conditions were used.[59] As the other

compounds were not soluble in benzene, the reactions were carried out in THF.Weakly

coordinatingtriflatecomplex13wasshowntobesuperiortoallothercomplexes(TON:62)

13. This could indicate that coordination of nitrous oxide to the complex is necessary.

However,furtherstudiesarenecessarytogainmoreinsightintheactivationofN2OandH2

on the complex. 31P{1H}NMRof the reaction solution revealed that the complexwas still

intactaftercatalysis.

Inanattempttooptimisethereactionconditions,thereactiontimewasprolongedwhile13

wasusedasacatalyst(figure31).ThisresultedinaTONof430basedontheformationof

H2O,whichisthebestperforminghomogeneouscatalystfortheactivationofN2OwithH2at

thismomenttoourknowledge,evenunderremarkablymildreactionconditions.

36

Figure31.Homogeneouslycatalysedhydrogenationofnitrousoxidebycomplex13gavethehighest

TONforthisreaction.Thiscomplexcanbeconsideredasthebestperforminghomogeneouscatalyst

forthisreactionatthismoment.

Althoughnoevidenceispresentyet,acatalyticcyclecouldbeenvisioned,asshowninfigure

32. As in other similar studies on nitrous oxide activation,[57,58] hydrogen activation is

proposed to take place first to afford complexB. The bondingmode of hydrogen on the

metalcomplexwasnotdeterminedyet.ThisstepisfollowedbyanoxygentransferfromN2O

togivecomplexC,andthereleaseofwaterandcoordinationoftheligandcouldregenerate

A. However, thorough investigation on the catalytic mechanism is required to present a

proposalofthegenuinereactionsequenceofthehydrogenationofnitrousoxide.

Figure 32. Envisioned catalytic mechanism for the hydrogenation of nitrous oxide by Rh(I)Pt(II)

complexesinvestigatedinthiswork.

PPh2

Rh

Ph Ph

Pt

OTf

THF, RT, 3 daysTON: 430

N2O + H21 bar 1 bar H2O + N2

H2

H2O

N2O

N2

L

L

RhPt=

PPh2Rh

Ph PhPt

LRhPtRhPt

RhPt

L

H2

H2O

B

CA

37

2.5HeterobimetallicComplexes–OtherGroup9Metals(Iridium&Cobalt)

Besides the synthesis and analysis of Rh(I)Pt(II) dinuclear compounds, the preparation of

other group 9 metal bimetallic complexes was studied. First, the synthesis of iridium

complexes using the TMSC≡CTropPPh2 ligand and different iridium dimer precursors were

examined (figure 33). However, the synthesis of these complexeswas not successful and31P{1H}NMRdatashowedmultiplesignals,whichcouldnotbeexplained,butindicatedthat

iridiumcomplexeswerenotformed.

Figure33.Attemptedsynthesisofhomobimetalliciridium(I)TMSC≡CTropPPh2complexes.

Then,thepreparationofcobalt(I)complexeswasstudied,butthehypothesizedcomplexes

werenotobtainedandNMRdatagavenoconclusionabouttheformedspecies(figure34).It

couldbearguedthatformationofbothcomplexeswasnotpossible,sincereplacingthePPh3

groups by the trop ligand is not favourable. The synthesis of homobimetallic iridium

1 eq [Ir(C2H4)2Cl]2

Benzene

Ph2P

TMSTMS

PPh2

Ir

TMS TMSIr

Ph2P

Ir

TMSTMSIrCl

ClCl

Cl

1 eq [Ir(C2H4)2Cl]2 AgOTf

DCM

Ph2P

TMSTMS

O

OS

PPh2

Ir

TMS TMSIr

O

OSOCF3

CF3

O

1 eq [Ir(COE)2Cl]2

Benzene

Ph2P

TMSTMS

PPh2

Ir

TMS TMSIr

Ph2P

Ir

TMSTMSIrCl

ClCl

Cl

38

PhC≡CTropPPh2complexeswasalsoinvestigated(figure35).However,thesecomplexescould

notbesynthesizedsuccessfully.Apossibleexplanationfortheunsuccessfulpreparationof

theiridiumTMSC≡CTropPPh2andPhC≡CTropPPh2complexesisthattheinsertionofiridiuminthis

chelatingligandisstericallyandelectronicallynotfeasible.

Figure34.Attemptedsynthesisofhomobimetalliccobalt(I)TMSC≡CTropPPh2complexes.

Figure35.Attemptedsynthesisofhomobimetalliciridium(I)PhC≡CTropPPh2complexes.

2 eq [Co(PPh3)2Cl]

THF

Ph2P

TMSTMS

PPh2

Co

TMS TMSCo

Ph2P

Co

TMSTMSCoCl

ClCl

Cl

1 eq [Co(PPh3)2Cl]

THF

Ph2P

TMSTMS

PPh2

Co

Ph Ph

Cl

PPh3

1 eq [Ir(C2H4)2Cl]2

CD2Cl2

Ph2P

PhPh

PPh2

Ir

Ph PhIr

Ph2P

Ir

PhPhIrCl

ClCl

Cl

1 eq [Ir(C2H4)2Cl]2 AgOTf

ACN

Ph2P

PhPh

O

OS

PPh2

Ir

Ph PhIr

O

OSOCF3

CF3

O

39

3.Conclusion&Outlook

Inconclusion,sixnewheterobimetallicRh(I)Pt(II)withanoveltypeofchelatingligandwere

synthesisedandcharacterised.Severalofthesecompoundswerefoundtobeactive inthe

homogeneously catalysed hydrogenation of nitrous oxide under mild conditions, yielding

water and nitrogen. The highest TON was achieved using catalyst 13, which is to our

knowledge the best performing catalyst for this reaction at this moment. This reaction

catalysed by a heterobimetallic Rh(I)Pt(II) complex offers a green, efficient and mild

procedurefortheremovalofthegreenhousegasnitrousoxide.

Furthermore,NMRandXRDstudiesrevealedthat longerRh-Ptbondlengthscorresponded

toaweakerRh-PtcouplinginNMR,whileashortermetal-metalbondlengthisrelatedtoa

strongercoupling.Additionally,alongermetal-metalbondwasinagreementwithaweaker2JPPtmeasuredin31P{1H}NMRandviceversa,whichimpliesthatinformationabouttheRh-Pt

bondlengthcouldalreadyberetrievedfromanaccessible31P{1H}spectrum.

In general, a shorter rhodium-platinum bond was observed for the cationic bimetallic

complexescomparedtotheneutralcompounds.Exceptionfromthiseffectwascomplex14,

wherethelongestRh-Ptbondlengthwasmeasured(2.788(4)Å),whichcouldbeexplained

by steric reasons upon formation of the dimer. Moreover, further studies on the metal-

metal bond suggested that an electron rich Pt(II) is essential for the Rh-Pt bond, which

indicatedthattheplatinummostlikelyactasanelectrondonatingsupportingmetalloligand.

Furtherresearch isrequiredtofindoutwhetheraheterobimetallicsystemissuperiortoa

homo(bi)metallicsystem intheactivationofN2OwithH2.Thiscouldthenbetheevidence

that the presence of two different metal centres indeed enhances the catalytic activity.

Moreover,additionalstudiesarenecessarytogainmoreinsightinthecatalyticmechanism

ofthisreaction.StoichiometricreactionsofthecomplexeswithN2O,H2,H2OandN2could

give insight into the activation of the substrates and the steps in the catalytic cycle.

Additionally, the reaction set-up should be improved in order to determine the precise

amount of gasses used and produced. Furthermore, the internal standard should be

40

calibrated. These actions should then lead to amore accurate determination of the TON

basedontheamountofH2O,determinedby1HNMRandN2,determinedbyGC.Besides,a

homogeneitytestisnecessaryinordertoruleoutthepossibilitythatnanoparticlesandnot

theheterobimetalliccomplexcatalysethehydrogenationofnitrousoxide.Scanningelectron

microscope (SEM) images of the reaction mixture after catalysis should give information

aboutanynanoparticleformation.

41

4.ExperimentalSection

General techniques:Allexperimentswereperformedunderan inertatmosphereofargon

using standard Schlenk and glove-box (argon atmosphere) techniques unless otherwise

specified.DCM,THF,toluene,diethylether,n-hexaneandacetonitrilewerepurifiedusingan

InnovativeTechnologiesPureSolvsystem.DeuteratedsolventswerepurchasedfromEuriso-

Top,degassedanddistilledfromtheproperdryingagent,andstoredovermolecularsieves.

Chemicals:BasicchemicalswereorderedatABCR,Acros,Aldrich,Fluka,LancasterorSTREM.

The following organic compounds and metal precursors were prepared by literature

methods:Br2TropOH[60],[Rh(C2H4)2Cl]2[61],[(Me)2Pt(SMe2)]2[62].PhC≡CTropCl7wassynthesised

accordingtoearlierresultsofthehostgroup.

IRspectrawererecordedonaPerkin-Elmer-Spectrum2000FT-IR-Ramanspectrometer.The

absorptionbandsaredescribedasfollows:strong(s),verystrong(vs),middle(m),weak(w),

orbroad(br).

NMRspectrawererecordedonBrukerAvance200,300,400and500MHzspectrometersat

298 K (if not indicated differently). Chemical shifts (d) are reported in ppm. The absolute

valuesofthecouplingconstants(J)aregiveninHertz(Hz).Multiplicitiesareabbreviatedas

singlet(s),doublet(d),triplet(t),quartet(q)andbroad(br).Spectrawerereferencedwith

externalstandards:for1Hand13CNMRwithTMS,for19FNMRwithCFCl3,for31PNMRwith

H3PO4,for103RhNMRwithRh(acac)3andfor195PtNMRwithK2PtCl6.Quaternarycarbonsare

indicated as Cquat, aromatic carbons as CHarand protons as Har. The benzylic protons and

carbon atoms in the central seven-membered ring are indicated as Hbenz and CHbenz,

respectively.

X-raySinglecrystalssuitableforX-raydiffractionwerecoatedwithpolyisobutyleneoilunder

inertatmosphere,transferredtoanylonloopandthentransferredtothegoniometerofa

BrukerX8APEX2orD8-VenturediffractometeroronanOxfordExcaliburequippedwitha

molybdenumX-ray tube (λ=0.71073Å).Preliminarydatawas collected todetermine the

crystalsystem.ThespacegroupwasidentifiedandthedatawereprocessedusingtheBruker

SAINT+ program and corrected for absorption using SADABS. The structures were solved

usingdirectmethods(SHELXS)onOLEX2completedbyFouriersynthesisandrefinedbyfull-

matrixleast-squaresprocedures.

42

10,11-Di-(phenyl)acetylene-5H-dibenzo[a,d]cyclohepten-5-diphosphine:PhC≡CTropPPh2(8)

MF:C43H29P

MW:576.66PhC≡CTropCl(2.84g,6.64mmol)wasdissolvedintoluene(30mL)andn-hexane(15mL)and

diphenylphosine(1.2mL,1.2g,6.64mmol,)wasaddedtotheclearorangebrownsolution.

The reactionmixturewas stirred at 50°C over theweekend,while yellow precipitatewas

formed.Thesolutionmixturewasheated to reflux for30minutesandafter itwascooled

downdegassedNa2CO3(12mL,10%inH2O)wasadded.Thesolutionwasheatedat50°Cfor

3hoursbefore itwasheatedunderrefluxfor30minutes.Aftercoolingdown,thetoluene

phasewas separated from the aqueous phase and this phasewas extractedwith toluene

twice(2x10mL).Thesolventwasevaporatedandthebrown/orangeoilwastreatedwithn-

hexane. The brown/orange powder was stirred vigorously in acetonitrile (24 mL) and a

yellowpowderwasprecipitatedoutofthesolution.Theproductwasfiltrated,washedwith

hexane(12mL)anddriedundervacuum.Thefiltratewasplacedinthefreezerovernightand

after filtrationasecondbatchof theyellowproductwasobtained,whichwasdriedunder

vacuum.Yield:2.4g(63%).Yellowcrystalswereobtainedbyslowdiffusionofn-hexaneina

solutionof8indiethylether.

1HNMR(300MHz,CDCl3):δ(ppm)4.70(d,2JPH=5.7Hz,1H,Hbenz),6.89(d,3JHH=7.4Hz,2H,

Har),7.01-7.15(m,10H,Har),7.22-7.29(m,10H,Har),7.55-7.59(m,4H,Har),7.82(d,3JHH

=7.5Hz,2H,Har).–13CNMR(75.5MHz,CDCl3):55.41(d,1JCP=21.32Hz,1C,CHbenz),90.99

(s,2C,C≡CPh,Cquat),96.73(s,2C,C≡CPh,Cquat),122.73(s,2C,Cquat),125.73(d,4JCP=1.4

Hz,2C,CHar),126.86(d,3JCP=6.5Hz,4C,CHar),127.33(s,4C,CHar),127.43(d,4JCP=7.4Hz,

2C,CHar),128.10(d,3JCP=3.6Hz,2C,CHar),128.15(s,4C,CHar),129.13(d,4JCP=1.7Hz,2C,

CHar),129.21(d,4JCP=6.3Hz,2C,Colefintrop),130.74(s,4C,CHar),132.54(d,2JCP=19.7Hz,4

C,CHar),133.63(d,3JCP=4.4Hz,2C,Cquat),137.05(d,1JCP=19.6Hz,2C,Cquat),149.99(d,2JCP

=8.9Hz,2C,Cquat).–31PNMR(121.5MHz,CDCl3):δ(ppm)-12.95(s,1P,PPh2).

43

[(PhC≡CTropPPh2)2Rh2(μ-Cl)2](9)

MF:C86H58Cl2P2Rh2

MW:1430.04

[Rh2(μ-Cl)2(C2H4)4](344.9mg,0.89mmol)and8(852.4mg,1.48mmol)werecombinedina

flaskandstirredinbenzene(10mL)for3hoursatroomtemperature.Thesolutionmixture

was placed in a fridge overnight. The orange product was filtrated and washed with n-

hexane(5mL)anddriedinvacuo.Thefiltratewaslayeredwithn-hexaneandasecondbatch

of the product was obtained after recrystallization. Yield: 1000.6 mg (79%). Red crystals

wereattainedbyslowdiffusionofn-hexaneinasolutionof9indichloromethane.

1HNMR(300MHz,CD3CN):δ(ppm)5.10(dd,2JPH=14.9Hz,2JRhH=1.7Hz,1H,Hbenz),7.03(d,3JHH=7.4Hz,2H,Har),7.23–7.30(m,10H,Har),7.35–7.43(m,10H,Har),7.63–7.71(m,4

H,Har),8.56(d,3JHH=7.5Hz,2H,Har).–13CNMR(75.5MHz,CD3CN):δ(ppm)50.57(d,1JCP=

26.1Hz,1C,CHbenz),54.13(m,2C,Colefintrop),94.52(s,2C,C≡CPh),95.71(s,2C,C≡CPh),

125.35(s,2C,Cquat),128.27(s,2C,CHar),128.65(d,3JCP=10.9Hz,4C,CHar),129.25(s,2C,

CHar),129.78(s,4C,CHar),130.19(s,2C,CHar),130.31(d,4JCP=6.4Hz,4C,CHar),131.10(d,1JCP=52.6Hz,2C,Cquat),131.56(d,3JCP=2.5Hz,2C,CHar),131.82(s,4C,CHar),135.20(d,2JCP=9.7Hz,4C,CHar),136.91(d,3JCP=4.5Hz,2C,Cquat),137.80(dd,2JCP=7.7Hz,2C,Cquat).

–31PNMR(121.5MHz,CD3CN):δ(ppm)93.70(d,1JPRh=186.5Hz,1P,tropP).–103RhNMR

(15.8MHz,CD3Cl3):δ (ppm) -6926(d, 1JRhP=237.2Hz).– IR (ATR):3052(w,νCH),3017(w,

νCH),2992(w,νCH),1479(s),1434(s),1260(m),1097(m),1024(m),791(m).

[(PhC≡CTropPPh2)Rh(Cl)Pt(CH3)2](10)

MF:C45H35ClPPtRh

MW:940.17

9 (500.0 mg, 0.35 mmol) and [(Me)2Pt(SMe2)]2 (241.1 mg, 0.42 mmol) were stirred in

dichloromethane(20mL)for3hours.Afterremovalofthesolventtheproductwaswashed

withn-hexaneanddriedinvacuo.Yield:558.7mg(85%).Redcrystalsweregrownbyslow

diffusionofn-hexaneinasolutionof10indichloromethane.

1HNMR(300MHz,CD2Cl2):δ(ppm)1.46(s,2JPtH=92.4Hz,6H,Pt(CH3)2),4.92(d,2JPH=14.4

Hz,1H,Hbenz),7.04(d,3JHH=7.1Hz,2H,Har),7.19–7.42(m,10H,Har),7.45–7.53(m,6H,

44

Har),7.70–7.76(m,4H,Har),7.90–7.93(m,4H,Har),7.13(d,3JHH=7.5Hz,2H,Har).–13C

NMR (75.5 MHz, THF-d8): δ (ppm) 12.08 (s, 2 C, Pt(CH3)2), 40.13 (d, 1JCRh = 2.2 Hz, 1 C,

Colefintrop),40.31(d,1JCRh=2.1Hz,1C,Colefintrop),49.52(d,1JCP=27.2Hz,1C,CHbenz),91.41(s,

2C,C≡CPh),122.89(s,2C,Cquat),126.73(s,2C,C≡CPh),126.96(s,2C,CHar),127.15(d,3JCP

=10.4Hz,4C,CHar),129.25(s,2C,CHar),128.26(s,4C,CHar),128.70(s,2C,CHar),129.11(d,

4JCP=6.5Hz,2C,CHar),129.79(d,4JCP=2.4Hz,4C,CHar),130.53(d,1JCP=46.8Hz,2C,Cquat),

131.56(d,3JCP=2.5Hz,2C,CHar),131.52(s,4C,CHar),133.58(d,2JCP=10.2Hz,4C,CHar),

136.32(d,3JCP=7.2Hz,2C,Cquat),135.39(m,2C,Cquat).–31PNMR(121.5MHz,THF-d8):δ

(ppm)89.88(d,1JPRh=217.5Hz,2JPPt=519.9Hz,1P,tropP).–103RhNMR(15.8MHz,THF-d8):

δ(ppm)-7045(d,1JPRh=215.2Hz).–195PtNMR(64.4MHz,THF-d8):δ(ppm)-3274(dd,2JPtP=

530.1Hz,1JPtRh=83.4Hz)

[(PhC≡CTropPPh2)Rh(CH3CN)Pt(CH3)2]PF6(11):

MF:C47H38F6NP2PtRh

MW:1090.73

9(100mg,0.07mmol)and[(Me)2Pt(SMe2)]2(40.2mg,0.07mmol)werecombinedinaflask

andflushedwithdichloromethane(5mL).Thereactionmixturewasstirredforonehourat

roomtemperature,beforeasolutionofTlPF6(48.9mg,0.14mmol)inacetonitrile(5mL)was

added. After one hour the mixture was filtrated over Celite and washed with

dichloromethane(5mL).Thesolventwasevaporatedandtheredproductwaswashedwith

n-hexane (10mL)anddried invacuo.Yield:96.6mg (63%).Redcrystalswereobtainedby

slowdiffusionofn-hexaneinasolutionof11indichloromethane.

1H NMR (300MHz, CD2Cl2): δ (ppm) 1.35 (s, 2JPtH = 92.4 Hz, 6 H, Pt(CH3)2), 2.14 (s, 3 H,

CH3CN),4.98(dd,2JPH=15.4Hz,2JRhH=2.3Hz,1H,Hbenz),7.13(d,3JHH=7.2Hz,2H,Har),7.29

–7.40(m,10H,Har),7.46–7.62(m,10H,Har),7.89-7.93(m,4H,Har),8.14(d,3JHH=7.3Hz,

2H,Har).–13CNMR(75.5MHz,CD2Cl2):δ(ppm)3.40(s,1C,CH3CN),10.09(s,2C,Pt(CH3)2),

50.43 (d, 1JCP= 27.2Hz, 1 C, CHbenz), 71.79 (d, 1JRhH = 4.0Hz, 2 C, Colefintrop), 89.56 (s, 2 C,

C≡CPh), 95.77 (s, 2 C, C≡CPh), 121.84 (s, 2 C, Cquat), 128.38 (s, 2 C, CHar), 128.88 (s, 1 C,

CH3CN),129.06(d,1JCP=47.1Hz,2C,Cquat),129.37(d,3JCP=10.5Hz,4C,CHar),129.54(s,4

C,CHar),129.91(s,2C,CHar),130.15(d,4JCP=6.7Hz,2C,CHar),131.13(s,4C,CHar),132.34

(d,3JCP=2.6Hz,2C,CHar),132.82(s,4C,CHar),132.97(d,3JCP=7.2Hz,2C,Cquat),133.35(d,

45

2JCP=10.2Hz,4C,CHar),135.70(m,2C,Cquat).–31PNMR(121.5MHz,CD2Cl2):δ(ppm)91.40

(d,1JPRh=197.9Hz,2JPPt=537.4Hz,1P,tropP),-144.45(hept,1JFP=708.5Hz,1P,PF6).–19F

NMR(188.3MHz,CD2Cl2):δ(ppm)-72.92(d,1JFP=710Hz,1P,PF6).–103RhNMR(15.8MHz,

CD2Cl2):δ(ppm)-7207(d,1JPRh=196.2Hz).–195PtNMR(64.4MHz,CD2Cl2):δ(ppm)-3223

(dd,2JPtP=546.7Hz,1JPtRh=104.1Hz).–IR(ATR):3052(w,νCH),2959(m,νCH),2900(w,νCH),

1480(s),1434(s),1260(m),1095(m),1024(m),791(m).

[(PhC≡CTropPPh2)Rh(CH3CN)Pt(CH3)2]BArF(12)

MF:C79H50BF24NPPtRh

MW:1808.98

9 (100.0mg, 0.07mmol) and [(Me)2Pt(SMe2)]2 (36.2mg, 0.06mmol)were combined in a

flask and flushedwith dichloromethane (5mL). The reactionmixturewas stirred for one

houratroomtemperature,beforeasolutionofNaBArF(123.9mg,0.14mmol)inacetonitrile

(5mL)was added. After one hour themixturewas filtrated over Celite andwashedwith

dichloromethane(5mL).Thesolventwasevaporatedandtheredproductwaswashedwith

n-hexane(10mL)anddriedinvacuo.Yield:145.9mg(58%).Redcrystalswereobtainedby

slowdiffusionofn-hexaneinasolutionof12intoluene.

1HNMR(300MHz,CD2Cl2):δ(ppm)1.35(s,2JPtH=87.9Hz,6H,Pt(CH3)2),2.12(s,3H,CH3CN),

4.94(dd,2JPH=15.3Hz,2JRhH=2.4Hz,1H,Hbenz),7.10(d,3JHH=7.3Hz,2H,Har),7.29–7.42

(m,10H,Har),7.42–7.52(m,6H,Har),7.56(brs,4H,BArF),7.58–7.67(m,4H,Har),7.72

(brs,8H,BArF),7.88–7.95(m,4H,Har),8.15(d,3JHH=7.6Hz,2H,Har).–13CNMR(75.5

MHz,CD2Cl2):δ (ppm)3.29 (s,1C,CH3CN),9.97 (s,2C,Pt(CH3)2),45.63 (d,2C,Colefintrop),

50.80(d,1JCP=27.3Hz,1C,CHbenz),95.93(s,2C,C≡CPh),117.86(s,BArF),121.71(s,2C,

Cquat),123.17(s,2C,C≡CPh),126.78(s,1C,CH3CN),128.38(s,2C,CHar),128.66(q,BArF),

128.70(d,1JCP=39.7Hz,2C,Cquat),129.34(d,3JCP=10.6Hz,4C,CHar),129.55(s,4C,CHar),

129.99(s,2C,CHar),130.25(d,4JCP=6.7Hz,2C,CHar),130.89(q,BArF),131.22(s,4C,CHar),

132.35(d,2C,CHar),132.81(s,4C,CHar),132.94(d,3JCP=8.6Hz,2C,Cquat),133.29(d,2JCP=

10.5Hz,4C,CHar),135.18(s,BArF),135.50(d,2C,Cquat),162.13(q,1JBC=49.7Hz,BArF).–31P

NMR(121.5MHz,C6D6):δ(ppm)91.26(d,1JPRH=197.9Hz,2JPPt=537.9.1Hz,1P,tropP).–19FNMR(188.3MHz,C6D6):δ(ppm)-62.83(s,24F,BArF).–11BNMR(C6D6):δ(ppm)-6.60(s,

46

1B,BArF).–103RhNMR(15.8MHz,CD2Cl2):δ(ppm)-7304(d,1JPRh=200.3Hz).–195PtNMR

(64.4MHz,CD2Cl2):δ(ppm)-3196(dd,2JPtP=538.0Hz,1JPtRh=109.3Hz).

[(PhC≡CTropPPh2)Rh(OTf)Pt(CH3)2(13)

MF:C47H39F3O3PPtRhS

MW:1069.84

10(50.0mg,0.053mmol)wasstirredwithAgOTf(13.7mg,0.053mmol)inTHF(3mL)for3

hours.Theprecipitateofsilver(I)chloridewasremovedbyfiltrationoverCelite.Thefiltrate

solution was layered with n-hexane and after recrystallization orange crystals were

obtained.Thesolutionwasremovedandtheproductwaswashedwithn-hexaneanddried

invacuo.Yield:37.0mg(69%).

1HNMR(300MHz,THF-d8):δ(ppm)1.47(d,2JPtH=90.1Hz,6H,Pt(CH3)2),5.14(d,2JPH=14.3

Hz,1H,Hbenz),7.12(d,3JHH=7.6Hz,2H,Har),7.19–7.39(m,10H,Har),7.50–7.57(m,6H,

Har),7.69–7.73(m,4H,Har),7.96–8.02(m,4H,Har),8.22(d,3JHH=7.8Hz,2H,Har).-13C

NMR (75.5 MHz, THF-d8): δ (ppm) 10.11 (s, 2 C, Pt(CH3)2), 45.27 (d, 1JCRh = 2.1 Hz, 2 C,

Colefintrop),50.41(d,1JCP=28.9Hz,1C,CHbenz),91.95(s,2C,C≡CPh),94.66(s,2C,C≡CPh),

123.71(s,2C,Cquat),128.48(s,2C,CHar),128.67(s,2C,CHar),128.95(d,3JCP=10.4Hz,4C,

CHar),128.99(d,4JCP=3.0Hz,4C,CHar),129.26(s,2C,CHar),129.83(d,1JCP=46.6Hz,2C,

Cquat),129.97(s,4C,CHar),130.83(d,4JCP=6.4Hz,2C,CHar),130.92(s,2C,CHar),131.96(d,3JCP=2.7Hz,2C,CHar),133.31(s,4C,CHar),134.95(d,2JCP=10.1Hz,4C,CHar),137.19(d,JPH

=2.8Hz,2C,Cquat).–31PNMR(121.5MHz,THF-d8):δ(ppm)91.60(d,1JPRH=211.8Hz,2JPPt=

519.0Hz,1P, tropP).– 19FNMR(188.3MHz,THF-d8):δ (ppm)-78.4 (s,OTf).– 103RhNMR

(15.8MHz,THF-d8):δ(ppm)-6737(d,1JPRh=210.6Hz).–195PtNMR(64.4MHz,THF-d8):δ

(ppm)-3263(dd,2JPtP=519.4Hz,1JPtRh=94.5Hz).

[(PhC≡CTropPPh2)2Rh2Pt2((CH3)2)2(μ-Cl)]BArF(14)

MF:C122H82BClF24P2Pt2Rh2

MW:2708.09

7(100.0mg,0.11mmol)wasstirredwithNaBArF(47.1mg,0.053mmol)inTHF(5mL).After

1 hour, the reactionmixturewas filtrated over Celite. The solvent was removed and the

47

product was washed with n-hexane and dried under vacuum. Yield: 79.9 mg (38%). Red

crystalsweregrownbyslowdiffusionofn-hexaneinasolutionof9intoluene.

1HNMR(300MHz,THF-d8):δ(ppm)1.47(s,6H,Pt(CH3)2),5.28(d,2JPH=14.6Hz,1H,Hbenz),

7.12–7.38(m,12H,Har),7.48–7.53(m,6H,Har),7.57(brs,4H,BArF),7.79(brs,8H,BArF),

7.80–7.85(m,4H,Har),7.92–8.00(m,4H,Har),8.16(d,3JHH=7.8Hz,2H,Har).–13CNMR

(75.5MHz,THF-d8):δ(ppm)10.12(s,2C,Pt(CH3)2),48.09(d,2C,Colefintrop),49.48(d,1JCP=

27.7Hz,1C,CHbenz),91.54(s,2C,C≡CPh),92.49(s,2C,C≡CPh),117.20(s,BArF),121.29(s,

2C,Cquat),125.62(s,2C,CHar),127.50(d,1JCP=38.7Hz,2C,Cquat),127.85(d,3JCP=10.9Hz,4

C,CHar),129.55(s,4C,CHar),128.77(s,4C,CHar),128.92(q,BArF),129.17(q,BArF),129.48

(s,4C,CHar),129.56(d,4JCP=6.8Hz,2C,CHar),130.60(d,2C,CHar),132.02(s,4C,CHar),

133.79 (d, 2JCP = 10.0 Hz, 4 C, CHar), 132.24 (d, 3JCP = 4.6 Hz, 2 C, Cquat), 134.62 (s, BArF),

135.58(d, 3JCP=2.7Hz,2C,Cquat),161.84(q, 1JBC=49.6Hz,BArF).–31P-NMR(121.5MHz,

THF-d8): δ (ppm) 88.76 (d, 1JPRh= 215.6Hz, 2JPPt= 505.7Hz, 1 P, tropP). – 19F-NMR (188.3

MHz,THF-d8):δ(ppm)-62.87(s,24F,BArF).–11BNMR(THF-d8):δ(ppm)-6.46(s,1B,BArF).

–103RhNMR(15.8MHz,THF-d8):δ(ppm)-7491(d,1JPRh=209.1Hz).–195PtNMR(64.4MHz,

THF-d8):δ(ppm)-3321(br).

[(PhC≡CTropPPh2)2Rh2Pt2((CH3)2)2(μ-ClTlCl)]BArF(15)

MF:C122H82BCl2F24P2Pt2Rh2Tl

MW:2947.94

7 (8.8 mg, 0.0094 mmol) and TlBArF (10.3 mg, 0.0096 mmol) were combined in 1 mL

benzeneandstirredfor1hour.ThereactionmixturewasfilteredoverCeliteandthefiltrate

waslayeredwithn-hexane.Slowdiffusionresultedincrystallisationoftheorangeproduct.

1HNMR(300MHz,THF-d8):δ(ppm)1.50(s,6H,Pt(CH3)2),5.28(d,2JPH=14.6Hz,1H,Hbenz),

7.17(d,3JHH=6.3Hz,2H,Har),7.19–7.41(m,10H,Har),7.48–7.51(m,6H,Har),7.57(brs,

4H,BArF),7.78(brs,8H,BArF),7.83–7.91(m,4H,Har),7.95(m,4H,Har),8.14(d,3JHH=7.8

Hz,2H,Har).–31PNMR(121.5MHz,THF-d8):δ(ppm)90.12(d,1JPRh=218.9Hz,2JPPt=513.6

Hz,1P, tropP). 13C, 195Ptand 103RhNMRwerenotmeasured, since therewasnotenough

compoundtomeasureadecentspectrum.

48

CatalytichydrogenationofN2O

InascrewcapSchlenckwereaddedcompoundX,mesityleneandTHF/benzene(2mL)inthe

quantities described in table x. After degassing the solution by three freeze pump thaw

cyclestheflaskwaschargedwith1barN2O.Thereactionsolutionwasfrozenand1barofH2

wasadded.Afterstirringfor22hoursatroomtemperaturethesolutionwasdegassedand

the amount H2O and TON were determined by 1H NMR of the reaction solution using

mesityleneasinternalstandard(table10).

Table10.Quantitiesofcomplex10-14andmesityleneusedinthecatalytichydrogenationofnitrous

oxide in different solvents. The amount of H2O and TON were determined using mesitylene as

internalstandard.

CompoundX Quantitycompound

(mg,μmol)

Quantitymesitylene

(mg,μmol)

QuantityH2O

(μmol)

TONbased

onH2O

10inTHF 7.5mg,8.0μmol 8.4mg,69.9μmol 85.2μmol 11

11inTHF - - - Noreaction

12inTHF 11.4mg,6.3μmol 7.8mg,64.9μmol 65.2μmol 11

12inBenzene 10.5mg,5.8μmol 8.5mg,70.7μmol 269.2μmol 47

13inTHF 8.1mg,7.6μmol 10.6mg,88.2μmol 464.2μmol 62

14inBenzene 8.7mg,3.2μmol 9.6mg,79.9μmol 21.0μmol 6

13inTHF,3

days

5.2mg,4.9μmol 10.0mg,83.2μmol 2080.0μmol 430

49

5.Appendix

ListofAbbreviations

ACN Acetonitrile

BArF Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate

Cu-ZSM-5 CopperZeoliteSoconyMobil–5

DCM Dichloromethane

DSC DifferentialScanningCalorimetry

HMQC Heteronuclearmultiple-quantumcoherence

Me Methyl

n-Hex n-Hexane

NMR Nuclearmagneticresonance

OTf Triflate

Ph Phenyl

QMID Quasimultipleiondetection

RT Roomtemperature

SEM Scanningelectronmicroscope

TGA Thermogravimetricanalysis

THF Tetrahydrofuran

TMS Trimethylsilyl

Tol Toluene

TON Turnovernumber

Trop 5-dibenzosuberene

XRD X-raydiffraction

50

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