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SYNTHESIS, STRUCTURE, AND REDOX REACTIVITY OF I !
Co3(CO)6(/i2-r]2,ri1-C(Ph)C=C(PPh2) C(O) SC(O) ) (/z2-PPh2)
THESIS
Presented to the Graduate Council of the
University of North Texas in Partial
Fulfillment of the Requirements
For the Degree of
MASTER OF SCIENCE
By
Trinidad Munoz, Jr., B.A.
Denton, Texas
May, 1994
37^
Al$i //<?. 7Q e
SYNTHESIS, STRUCTURE, AND REDOX REACTIVITY OF I !
Co3(CO)6(/i2-r]2,ri1-C(Ph)C=C(PPh2) C(O) SC(O) ) (/z2-PPh2)
THESIS
Presented to the Graduate Council of the
University of North Texas in Partial
Fulfillment of the Requirements
For the Degree of
MASTER OF SCIENCE
By
Trinidad Munoz, Jr., B.A.
Denton, Texas
May, 1994
37^
Al$i //<?. 7Q e
Munoz, Trinidad, Jr. Synthesis. Structure, and Redox
Reactivity of Co. (CO) . (//.-if. rf-C (Ph) C=C(PPh.) C(0) SC(O) ) (fj ,z_
PPh2j_. Master of Science (Chemistry), May, 1994, 40 pp., 4
tables, 7 illustrations, references, 34 titles.
The tricobalt cluster PhCCo3(CO)9 (l) reacts with the
bidentate phosphine ligand 2,3-bis(diphenylphosphino)maleic
thioanhydride (bta) with added Me3NO to yield
PhCCo3 (CO) 7(bta) (2), which upon heating overnight yields
Co3(C0) 6(/i2-ti2,ri1-C(Ph) C=C (PPh2) C(0) SC(O)) (fi2-PPh2) (3) .
Cluster (3) has been isolated and characterized by FT-IR
and 31P NMR spectroscopy. Structural determination of the
cluster has been demonstrated by X-ray diffraction
analysis. Cluster (3) is analogous to the cluster
synthesized by Richmond and coworkers. The redox
properties of (3) have been examined by cyclic voltammetry
and the data are reported within.
TABLE OF CONTENTS
Page
LIST OF TABLES iv
LIST OF FIGURES V
INTRODUCTION 1
Properties of the Tricobalt Cluster RCCo3(CO)9 Phosphine-substituted Tricobalt Clusters Phosphorus-carbon Bond Cleavage in Hydroformylation Processes ETC Reactions with Phosphine-substituted Tricobalt Clusters Reaction of PhCCo3(CO)9 with the bma ligand Reaction of PhCCo3(CO)9 with the bta ligand
EXPERIMENTAL 13
Solvents Reagents Instrumentation Preparation of Compound X-Ray Diffraction Structure
RESULTS AND DISCUSSION 18
Synthesis and Spectroscopic Properties of Cluster 3 X-Ray Diffraction Structure of Cluster 3 Cyclic voltammetric Studies of Cluster 3
REFERENCES 38
i n
LIST OF TABLES
Table Page
I X-Ray Crystallographic Collection and Processing
Data for Cluster 3 21
II Positional Parameters for Non-Hydrogen Atoms for
Cluster 3 with Estimated Standard Deviations in
Parentheses 22
III Selected Bond Distances ( A ) of Cluster 3 with
Estimated Standard Deviations in Parentheses 28
IV Selected Bond Angles (deg) of Cluster 3 with
Estimated Standard Deviations in Parentheses 31
IV
LIST OF FIGURES
Figure Page
1 Structure of a general /z3-alkylidyne
tricobaltnonacarbonyl cluster 2
2 Structure of 2,3-bis(diphenylphosphino)maleic
anhydride 9
3 Thermal reaction of PhCCo3(CO)9 and the bma
ligand which yields cluster 5 12
4 Reaction of PhCCo3(CO)9 and the bma ligand in the
presence of Me3NO which yields cluster 4 14
5 31P NMR spectrum of cluster 3 recorded at room
temperature in CDC13 16
6 ORTEP diagram of cluster 3 with the thermal
ellipsoids drawn at 50% probability level 22
7 Cathodic scan cyclic voltammogram of cluster 3
dichloromethane containing 0.25 M TBAP at
v = 0.1 V/s 32
SYNTHESIS, STRUCTURE, AND REDOX REACTIVITY OF I 1
co3(co) 6(/i2-n2/ti1-c(ph) c=c(pph2) c(o) sc(o)) (^2-pph2)
Introduction
The tricobalt cluster RCCo3(CO)9 in Figure 1 is a
well-known transition metal compound. The tetrahedral Co3C
unit is the core that comprizes a number of
methinyltricobalt enneacarbonyls of the general formula
RCO3(CO)9 (R = halogen, alkyl, aryl, carboxyl etc.)1. In
RCCo3 (CO) 9 clusters, six CO groups are equatorial and the
remaining three CO groups are axial. The molecule posseses
C3v symmetry with the equatorial CO groups bent out of the
Co3 plane toward the apical group. For compounds where the
apical group does not introduce additional congestion in
the molecule, the dihedral angle between the tricobalt
triangle and CoCO(eq)CO(eq) triangle is thirty degrees, on
the average. Robinson has shown that in the RCCo3(CO)9
cluster there is extensive electron delocalization in the
Co3C tetrahedral unit and that the reactivity of the
cluster is governed by the groups on the cobalt atoms or by
the apical substituent1. Ercoli and coworkers2 found that
the three axial CO groups exchange 14C0 faster than the
equatorial CO groups. The relative rates were found to be
in the order R = H < Br < CI < F2. These data reveal that
that the apical group is involved in reactivity modulation,
/ \ Figure 1. Structure of a general /*3-alkylidyne tricobaltnonacarbonyl cluster (R = halogen, alkyl, aryl, carboxyl etc.).
in a way analogous to the trans effect in inorganic
reactions1. In general, aryl derivatives are thermally
stable and resistant to oxidation. When the apical capping
group is a halogen atom there is susceptibility to
nucleophilic attack and hetereolytic fission at the C-X
bond. This is the reason that many simple derivatives of
these types of clusters cannot be isolated but instead
yield dimerized compounds1. The chemistry of the apical
group is due to the electronic and stereochemical nature of
the cluster. Physical features indicate properties not
consistant with a sp3 carbon atom. This can be explained
by viewing the Co3C core as electron withdrawing with
respect to the apical group. The high electron density in
the C-X group could be due to the polarization of the Co3C
core by a halogen atom or n bonding. To study the
electronic and stereochemical nature of the cluster, a
number of mono- and di-substituted tertiary phosphine and
arsine derivatives has been made3. These substituents have
been found to react reversibly with RCo3(CO)9 (R = CI, Br,
CH3, C6Hs) to yield compounds of the general formula
RCCO3 (CO) 8L and RCCO 3 (CO) 7L2. These compounds are air
stable, volatile, and do not decompose in non-polar
solvents3. The stability factor of these compounds has to
do with the ability of the RCCo3(CO)9 cluster to act as an
electron sink4. The structure of MeCCo3(CO)9 displays CO-CO
axial interactions, and that the clusters of RCCo3(CO)9 are
in general congested compounds. The structures adopted by
the phosphine and arsine-substituted clusters are those
that minimize the CO-CO interactions, which descibes why
equatorial substitution is observed despite the fact that
the apical group is distorted4.
Two reasons for the use of phosphine-substituted
complexes are altered product distribution and increased
catalyst stability5,6. For example, the [Co (CO) 3PBu3] 2
complex has been shown to exhibit unusual catalytic
properties. In the hydroformylation of olefins, it has
been found that the [Co(CO) 3PBu3]2 complex is catalytically
active at low pressures, yielding alcohols as the main
product rather than the expected aldehydes when compared to
Co2(CO)8 as a catalyst. It has also been shown that
[Co(CO) 3PBu3]2 is regioselective for the formation of the
terminal aldehyde when l-olefins5 are employed as a
feedstock. The use of ancillary phosphine ligands has
been extensively studied in catalytic hydrogenation and
hydrof ormylation reactions6,7'8,9. For example, the use of
the Me3CCo3 (CO) 7 (dppm) cluster, which contains the bidentate
bridging ligand bis(diphenylphosphino)methane (dppm) has
been shown to act as a catalyst for olefin
hydroformylation6 as does the PhCCo3(CO)9 cluster10. in
using these phosphine modified complexes, it has been
assumed that the metal-phosphine complex is more stable
than the parent cluster, but this has only been shown in
selected cases of mononuclear complexes and to even a
lesser degree in polynuclear complexes7. For example,
cyclometallation, a term which describes an intramolecular
metallation with formation of a chelate ring that contains
a metal-carbon bond11, and phosphorus-carbon bond clevage
are documented pathways in organometallic phosphine
complexes7,11.
Phosphorus-carbon bond cleavage has been observed in
Co and Rh based hydroformylation processes, although it was
ignored for a number of years due to the belief in tertiary
phosphine stablity. It was noted in 197212 that arenes or
alkanes were produced during the Rh4 (CO) 12/PR3 catalyzed
hydroformylation of olefins. Later this observation gained
attention and phosphorus - carbon bond cleavage was
identified as a mode for catalyst deactivation in Co and Rh
systems. In the Co system, for example, l-hexene
hydroformylation catalyzed by triarylphosphine cobalt
mixture, Co2 (CO) 8/PR3, showed evidence for phosphorus - carbon
bond cleavage. It was found that the Co catalysts lost
their catalytic activity due to loss of Co and the tertiary
phosphine11. Over a 28h period, 15-25% of phosphorus was
lost and 0.5 mol of benzene per mole of cobalt was observed
after 48 hours. It is clear that under certain conditions
the stable tertiary phosphine begins to take an active part
in the reaction chemistry of organometallic compounds.
Phosphorus-carbon bond activation is a mode of homogeneous
catalyst deactivation in hydroformylation (Rh and Co
catalyzed) and hydrogenation/dehydrogenation reactions.
Products of CO insertion are observed with the use of syn
gas which identifies R group migration from the phosphorus
to the metal as a mechanistic route11. From the limited
theoretical data13 available, migration of R from the
phosphine to the metal is thermodynamically and symmetry
allowed11.
Methods for catalytic and stoichiometric assistance of
ligand substitution have received attention over the years.
One such method is Electron Transfer Catalysis (ETC). The
initial single-electron-transfer is initiated either
electrochemically or by an added reagent14. Electron
transfer chain catalyzed reactions provide a method for
metal carbonyl cluster activation to nucleophilic
substitution. To study the stereochemical tone and the
synthetic usefullness of ETC, polydentate phosphine ligands
have been used in reactions with RCCo3(CO)9 (R = Ph, Me)
clusters. The decrease in catalytic efficiency with
increasing CO substitution, as in reactions with
monodentate ligands, could allow for regulated selective
syntheses of polydentate complexes15. Regioselectivity is
plausible for polydentate ligands. Stabilization of a 17-
electron site, created on a metal center by ETC by
coordination of one of the atoms of the polydentate ligand,
should result in the coordination of the second atom of the
polydentate ligand to the same metal center. For example,
the dimer (CF3) 2C2Co2 (CO) 3 (ttas) (where ttass = {o-
C6H4 [AsMe2] }2AsMe) possesses three arsine atoms coordinated
to one cobalt described as a distorted octahedron, with the
central arsine atom in a pseudoaxial site, and the outer
two arsine atoms in a pseudoequatorial site16. Options
have been explored to synthesize polydentate complexes of
different structural types to those obtained via thermal or
photochemical pathways. Electron initiated and thermal
reactions of the bidentate phosphine ligands Ph2PCH2PPh2
(dppm) and Ph2PCH2CH2PPh2 (dppe) have been investigated with
the RCCO3(CO)9 cluster (R = Ph, Me). It was found,
however, that there was no real advantage of ETC over
conventional thermal methods because of the ease in
controlling thermal reactions15.
The mechanism of ETC reactions with PhCCo3(CO)9 and
PPh3, dppm, dppe, and tpme has been elucidated. Bulk
electrolysis and transient electrochemical techniques
allowed for the clarification of the above ETC mechanisms.
Questions addressed in elucidating the ETC mechanism were
the role of the solvent, which could possibly stabilize an
intermediate, and the importance of homogeneous and
heterogeneous electron transfer following electrochemical
initiation since it has been assumed that homogeneous
electron transfer is facile16. In conducting electron
initiated substitution reactions of PhCCo3(CO)9 with PPh3,
dppm, and dppe, it was found that homogeneous electron
transfer from the Lewis base substituted cluster radical
anions is not rate-controlling. The efficiency and
specificity of the primary ETC reaction was found to vary
little with solvent. The coordination of solvent molecules
during reactions was not detected but the rate-determining
step was found to be solvent dependent. Lastly, the
addition of an electon to PhCCo3(CO)9 causes an increase in
the rate of substitution by mono or polydentate ligands16.
A unique bidentate phosphine ligand 2,3-
bis(diphenylphosphino)maleic anhydride (bma) in Figure 2,
synthesized by Fenske17,18,19 and used extensively by
Tyler20'21,22'23, has gained attention due to the interesting
stabilizing effect displayed with mononuclear complexes.
One such complex is the 19-electron complex Co(CO)3L2 (L =
bma)20. It has been shown that the stability in this
complex is attributed to electron delocalization into an
orbital that is Co-CO antibonding {%*). Occupation of
these orbitals has also been shown to weaken the Co-CO bond
which labilizes the compound toward dissociative CO loss.
Confirmation of this has been made through kinetic and ESR
studies20,22 . Other 19-electron adducts have been prepared7,0
by usi*ng the (bma) ligand and have been shown to exhibit
properties as the Co(CO)3L2 species (i.e. increased
stability and labilizing effects leading to dissociative CO
loss20.)
Figure 2. Structure of 2,3-bis(diphenylphosphino)maleic anhydride (P = PPh2) .
10
In this work the reaction between PhCCo3(CO)9 and the
bidentate phosphine ligand 2,3-bis(diphenylphosphino)maleic
thioanhydride (bta) has been examined as a part of a
continuing study on polynuclear clusters exhibiting redox-
active phosphine ligands7,24,25 . Richmond and coworkers have
previosly examined the reaction between PhCCo3(CO)9 and the
bidentate phosphine ligand 2,3-bis(diphenylphosphino)maleic
anhydride (bma). Their objective was to prepare the
cluster PhCCo3 (CO) 7(bma) (4) which would allow them to
investigate the redox properties and stability of the one
electron reduction product, [PhCCo3 (CO) 7bma] ". The effect
of the bma ligand on the cluster's redox properties could
be described by making comparisons with known
electrochemical data of the RCCo3(CO)7P2 clusters24,25'26,27 .
For example, Vahrenkamp and coworkers have reexamined the
electrochemistry of the methylidyne tricobalt cluster and
its phosphine-substituted derivatives. The initial
investigation of the parent cluster MeCCo3(CO)9 proved that
the [MeCCo3 (CO) 9] •" is kinetically labile, eliminating CO in
a reversible reaction. In phosphine-substituted clusters,
elimination of CO is more difficult, but the rate of CO re-
addition to the 47-electron intermediates increases26. It
is also noted that PR3 elimination competes with CO
elimination which becomes easier with increasing number of
phosphine ligands in the order PMe3< PMe2Ph < PMePh2 < PPh3.
The 47-electron intermediates formed have been shown to
11
react by different paths depending on whether CO or PR3 is
eliminated. When the tricobalt cluster is CO deficient
phosphine addition occurs in the presence of PR3 which
keeps the ETC process continuing. In the case of the
species being PR3, deficient further reduction leads to
stable 48-electron dianions26. The efficiencies of the
various reaction paths depend upon the type of phosphine
ligand and the degree of ligand substitution. The
monosubtituted phosphine tricobalt cluster
[MeCCo3 (CO) „PMe3] •" eliminates CO and PMe3 at the same rate,
which generates the ETC product MeCCo3 (CO) 7 (PMe3) 2,
[MeCCo3 (CO) 9] and [MeCCo3 (CO) 8] 2~. In the PPh3 cluster
derivatives, the reduction produces the 48-electron
[MeCCo3 (CO) 8]2" stable cluster26. For bis- and tri-
substituted phosphine clusters, it was found that the
elimination of CO is less important and that dianion
formation is predominate. The stability of [/x3-MeCCo3 (CO) 9.
n(PR3)n.J2-/1" (47e/48e) redox couple was also found to
increase. In other redox cycles examined, the 47- and 49-
electron intermediates are short-lived with eventual
conversion to the dianion or an ETC sequence producing the
paramagnetic species [MeCCo3 (CO) 9] " 2S. Turning now to the
PhCCo3(CO)9 and bma reaction, it was found that the initial
thermal reaction between PhCCo3(CO)9 and bma Figure 3 did
not yield the expected PhCCo3 (CO) 7(bma) cluster but rather
the Co3(CO) 6(/i2-r|2, r|1-C(Ph) C=C(PPh2) C(0) 0C(0)) (/i2-PPh2) (5)
12
U —
1
°y2f° CL CL
+
51—U
(C e
jQ
0)
4J TJ C rO
O U
o o u u s: 04
4-1 • O I f )
c u O 0)
-H 4J 4J 02 o 3 fd rH 0) u u
CO rH TJ f0 rH E a) M -H 0) > ,
JCJ EH 43
U -H
* X! ro £
0) T3 ^ a p m tJ) On
-H -H fa rH
13
cluster7. The reason for the formation of this unexpected
product presumably stems from electronic effects associated
with the bma ligand. The PhCCo3 (CO) 7(bma) intermediate is
considered to be a precursor to (5) based on evidence of
other diphosphine-bridged clusters, for example
PhCCo3 (CO) 7 (dmpe)28 and PhCCo3 (CO) 7 (dppf)
29. An alternate
route was used to prepare cluster 4 Figure 4, employing
Me3N013, PhCCo3(CO)9, and bma in THF. The PhCCo3 (CO) 7(bma)
was subsequently isolated and characterized by FT-IR and
31P NMR spectroscopies. Cluster 5 is formed by a
thermolysis reaction readily losing CO7.
In continuing this study the bidentate phosphine
ligand 2,3-bis(diphenylphophino)maleic thioanhydride (bta)
was prepared29. The focus of this research was then to use
this sulfur analoge of the bma ligand in conjuction with
the nido tricobalt cluster PhCCo3(CO)9 to prepare and
characterize Co3 (CO) 6(/x2-rj2,r|1-C(Ph) C=C (PPh2) C (0) SC(O) ) (fi2-
PPh2)(3). This also allowed for the investigation of the
redox properties of (3).
Experimental
I. Solvents
Tetrahydrofuran was distilled from sodium/benzophenone
ketyl. Dichloromethane and acetonitrile were distilled
from calcium hydride. The deuterated solvents
dichloromethane-d2 and chloroform-di were distilled from
P20s. All solvents upon distillation were then stored in
14
CL—U-
z co I <N <N
O U~
a.— U X
o U "
a D)
e
0) 4J T3 U
a) -U CO 3 U
« to — T3 O «H u a> —--H
o *
<W *
0 Si -H g; 4J V IW «5 o 0) tf <d
o c <D CO 0) a
a) u 3 0") 0)
"H XS fa 4J
15
Schlenk vessels under argon.
II. Reagents
Dicobalt octacarbonyl was purchased from Pressure
Chemical Company. Tetrachlorothiophene and trimethylamine
N-oxide dihydrate were purchased from Aldrich Chemical
Company. Chlorodiphenylphosphine and tetra-n-butylammonium
perchlorate (TBAP) were purchased from Johnson Matthey
Electronics and used as received. The 2,3-dichloromaleic
thioanhydride and Ph2PTMS were prepared by known
literature methods30'31. One should note that in preparing
the 2,3-dichloromaleic thioanhydride a small amount of 2,3
dichloromaleic anhydride will be present. The mixture can
not be completely separated. The 2,3-dichloromaleic
thioanhydride can be enriched through repeated
recrystallization in diethyl ether, which can be monitored
by gas liquid chromotography (GLC). The GLC of 2,3-
dichloromaleic thioanhydride, with an initial column
temperature of 100°C and a temperature increase of 20°C per
minute, shows a retention time of 6.55 minutes. There will
also be a small peak indicative of 2,3-dichloromaleic
anhydride which has a retention time of 2.99 minutes. The
PhCCo3(CO)9 cluster was prepared by the method used by
Seyferth and coworkers32. The 2,3-
bis(diphenylphosphino)maleic thioanhydride (bta) ligand was
prepared in the following manner. In a Schlenk flask to a
solution of 2,3-dichloromaleic thioanhydride in THF cooled
16
to 0° was added 2.1 equivalents of Ph2PSi (CH3) 3. The
solution turned form clear to dark red which was then
cooled to -70° to afford a black precipitate. The solution
was stirred for one hour, the solvent cannulated off, and
the black precipitate dried in vacuo overnight23. IR
(CH2C12) : V (CO) 1687 (s, C=0 ) cm'1. 31P NMR (CH2C12) : 6 17.7
(phosphine).
III. Instrumentation
Infrared spectra were recorded on a Nicolet 20SXB FT-
IR spectrometer using 0.lmm cells. The 31P NMR spectra
were recorded on a Varian 300-VXR spectrometer at 121 MHz.
The 31P chemical shift was referenced to external 85% H3P04,
taken to have 6=0. Cyclic voltammetric mesurements were
conducted on a PAR Model 273 potentiostat/galvanostat, with
IR compensation. The CV cell used was designed so that
mesurements could be made in an oxygen-free environment
employing standard Schlenk techniques. The electrodes used
in the mesurements were designed for the CV cell using a
platinum working electrode (area = 0.0079 cm2), a coiled
platinum wire as the counter electrode, and silver wire as
a psuedo-reference electrode.
IV. Preparation of Compound 3
In a schlenk tube containing 0.092g (1.77 mmol)
PhCCo3 (CO) 9 and 0.0 86g (1.77 mmol) bta was added two
equivalents of Me3NO along with 10 ml of THF. The color of
the solution became a dark brown-black in and evidence of
17
CO loss was apparent. The reaction was monitored by IR,
and after one hour the reaction was complete, yielding
initially PhCCo3 (CO) 7(bta) . Evidence of this product is
supported by previously published IR data on the
PhCCo3(CO) 7(bma) cluster. The solution was dried in vacuo,
yielding a dark brown solid. The solid was washed with
petroleum ether, dried and then dissolved in 10 ml of
dichloromethane. The mixture was heated overnight at 35
°C. On cooling, thin layer chromotography (TLC) showed the
presence of cluster (3) along with a small amount of
cluster (1). Cluster (3) was isolated by column
chromotography on silica gel using dichloromethane/
petroleum ether (1:1). Pure black crystals of cluster (3)
were obtained from dichloromethane/heptane (1:1). Yield:
0.163g (16%). IR (CH2C12) : v(CO) 2059 (m) , 2039 (vs) , 2021
(vs), 1926 (b,m), 1695 (m, asymmetric bta C=0), 1671 (m,
symmetric bta C=0) cm-1. 31P NMR (CDC13) : 6 199 (/i2-
phosphido) , 14 (phosphine) . Anal. Calcd for C41H25Co308P2S:
C, 53.73 (53.48); H, 2.75(2.94).
V. X-Ray Diffraction Structure
Single crystals for crystallographic analysis were
grown from a dichloromethane solution of (3) that had been
layered with heptane. A shiny black crystal of dimensions
0.05 x 0.08 x 0.22 mm was chosen and sealed inside a
Lindemann capillary and mounted on the goniometer of an
Enraf-Nonius CAD-4 diffractometer using Mo Ko radiation
18
monochromatized by a crystal of graphite. Cell constants
were obtained from a least-squares refinement of 25
reflections with 20 > 36°. Intensity data in the range of
2.0 < 20 < 44.0° were collected at 298 K using the <o scan
technique in the variable-scan speed mode. Three
reflections (600, 060, 117) were measured after every 3600
seconds of exposure time in order to monitor crystal decay
(<1%). The crystal structure was solved by SIR, revealing
the positions of the Co and P atoms. All remaining
hydrogen atoms were found by use of difference Fourier maps
and least-squares refinement. Excluding the phenyl
carbons, all non-hydrogen atoms were refined
anisotropically. Refinement converged at R = 0.0442 and Rw
= 0.0481 for 2591 unique reflections observed.
Results and Discussion
I. Synthesis and Spectroscopic Properties of Cluster 3.
The treatment of a mixture of PhCCo3(C0)9 and bta with
two equivalents of Me3NO at room temperature in THF yielded
PhCCo3 (CO) 7(bta) (2). The intermediate cluster is readily
detected by IR and is also supported by previously
published data on the PhCCo3 (CO) 7(bma) cluster7. The IR
spectrum of cluster 2 displays terminal carbonyl stretching
frequencies at 2065 (s), 2024 (vs), 2013 (s), 1996 (m),
1697 (m, symmetric bta C=0) cm"1. The asymmetic bta C=0
stretch, which should be present, is too weak and is not
discernable. Cluster 2 also shows bridging carbonyl
19
stretching frequencies at 1868 (b,m) , and 1838 (b,m) cm"1.
Upon heating of the PhCCo3 (CO) 7(bta) cluster, CO is lost to
yield cluster 3. One can say with confidence that this
reaction can be described as a unimolecular mechanism with
dissociative CO loss. A dissociative mechanism is in
keeping with the chemical nature of the Co3C clusters in
that the crowded environment around each cobalt atom would
make it difficult for the cluster to achieve a bimolecular
transition state33. Cluster 3 was isolated by column
chromotography over silica gel using dichloromethane/
petroleum ether (1:1). The IR spectrum of 3 displays
terminal carbonyl stretching frequencies at 2059 (m), 2039
(vs), 2021 (vs), 1926 (b,m) cm-l with the bta carbonyl
bands at 1695 (m, asymmetric C=0) and 1671 (m, symmetric
C=0) cm-l. The 31P NMR spectrum in Figure 5 shows a pair
of equal intensity resonances at 6 199 and 14, which can be
attributed to a fi2-phosphido and a coordinated Co-PR3
group, respectivly.
II. X-ray Diffraction Structure of Cluster 3.
Single shiny black crystals of cluster 3 were grown
and its molecular structure determined. No unusually short
inter- or intramolecular contacts exist within the unit
cell. The X-ray data and processing parameters are given
in Table I with fractional coordinates listed in Table II.
The ORTEP diagram in Figure 6 shows the presence of the
six-electron /i2-benzyl idene-rj2, i)1- (diphenylphosphino) maleic
20
Figure 5. 31P NMR spectrum of Cluster 3 recorded at room temperature in CDC13.
21
Table I: X-ray Crystallographic Collection and Processing Data for Cluster 3.
Space group
Cell constants
a, A
b, A
c, A
a, A
p , A
Y, A v, A3
Molecular formula
Molecular Weight
Molecules per cell (z)
p, gm cm"3
Abs. coeff. (/*) , cm"1
Radiation
Collection range, deg
Independent data, I > 3o(I)
R
Rw
Weights
PT
11.6053(8)
11.8438(8)
15.099(1)
105.169(5)
90.530(5)
104.976(6)
1928.5(2)
-̂'4X̂ 25̂ '® 3̂ 8̂ *2®
916.46
2
1. 578
14.58
MO
2° < 26 < 44°
2591
0.0442
0.0481
w = [0 . 04F2+ (oF) 2] -1
22
TABLE II: Positional Parameters for Non-Hydrogen Atoms for Cluster 3 with Estimated Standard Deviations in Parentheses.
Atom X y z B (A2)
Col 0 . 6517(1) 0 . 1531 1) 0 .23631(8) 2 .63(3)
Co2 0 .8251(1) 0 . 3239 1) 0 . 33579 (8) 2 .37(3)
Co3 0 . 7496(1) 0 . 3060 1) 0 . 16374(8) 2 .59(3)
S 0 .6595(2) 0 .4915 2) 0 .5078(2) 4 .11(7)
PI 0 .8005 (2) 0 . 1207 2) 0 .3005(2) 2 .85(6)
P2 0 .7935(2) 0 .5020 2) 0 .2367 (2) 2 .76(5)
01 0 .4254 (6) 0 . 0060 6) 0 .2727(5) 5 .8(2)
02 0 .6558(7) 0 . 0194 7) 0 .0480(5) 6 .1(2)
03 1 .0784(5) 0 .4134 6) 0 .3080(5) 4 .9(2)
04 0 .8784(7) 0 . 3477 7) 0 .5314(5) 5 .9 (2)
05 0 .6395(7) 0 .2864 8) - 0.0163(5) 7 .0(2)
06 0 .9656(6) 0 .2473 7) 0 .0876(5) 6 .0 (2)
012 0 .8490(6) 0 .6467 5) 0 .4737(4) 4 .3 (2)
014 0 .5076(6) 0 .2836 6) 0 .4240(4) 4 .4(2)
CI 0 .5172(8) 0 . 0654 8) 0 .2630 (6) 3 .5(2)
C2 0 .6622(9) 0 .0833 9) 0 .1214(7) 4 .3(3)
C3 0 .9792(8) 0 .3759 7) 0 .3160(6) 3 .2(2)
C4 0 .8533(8) 0 . 3377 7) 0 .4549(7) 3 .3 (2)
C5 0 .6810(8) 0 .2958 9) 0 .0545(6) 3 .7(2)
C6 0 .8844(9) 0 .2733 9) 0 .1191(6) 4 .1(3)
Cll 0 .7599(7) 0 .4717 7) 0 .3467(5) 2 .4(2)
TABLE I I : C o n t i n u e d .
2 3
A t o m X y z B ( A 2 )
C12 0 . 7 7 6 0 ( 8 ) 0 . 5 5 3 0 ( 7 ) 0 . 4 4 0 4 ( 6 ) 3 . 1 ( 2 )
C14 0 . 5 9 2 7 ( 7 ) 0 . 3 6 0 2 ( 7 ) 0 . 4 1 5 2 ( 6 ) 2 . 8 ( 2 )
C15 0 . 6 5 7 5 ( 7 ) 0 . 3 6 4 9 ( 7 ) 0 . 3 3 0 0 ( 6 ) 2 . 7 ( 2 )
C16 0 . 6 0 4 9 ( 7 ) 0 . 2 9 8 4 ( 7 ) 0 . 2 3 8 6 ( 6 ) 2 . 6 ( 2 )
C17 0 . 4 8 8 3 ( 7 ) 0 . 3 0 8 8 ( 7 ) 0 . 2 0 5 8 ( 6 ) 2 . 5 ( 2 ) *
C18 0 . 4 2 3 3 ( 8 ) 0 . 2 2 7 9 ( 8 ) 0 . 1 2 6 4 ( 6 ) 3 . 5 ( 2 ) *
C19 0 . 3 1 8 3 ( 9 ) 0 . 2 4 4 0 ( 9 ) 0 . 0 9 5 0 ( 7 ) 4 . 2 ( 2 ) *
C20 0 . 2 7 6 8 ( 9 ) 0 . 3 3 9 6 ( 9 ) 0 . 1 4 0 2 ( 7 ) 4 . 7 ( 2 ) *
C 2 1 0 . 3 3 7 2 ( 9 ) 0 . 4 1 8 8 ( 9 ) 0 . 2 1 8 9 ( 7 ) 4 . 6 ( 2 ) *
C22 0 . 4 4 3 3 ( 8 ) 0 . 4 0 5 5 ( 8 ) 0 . 2 5 1 0 ( 6 ) 3 . 4 ( 2 ) *
c m 0 . 9 1 9 7 ( 8 ) 0 . 0 6 7 2 ( 8 ) 0 . 2 4 2 8 ( 6 ) 3 . 2 ( 2 ) *
C112 1 . 0 3 9 4 ( 9 ) 0 . 1 1 7 7 ( 9 ) 0 . 2 7 4 8 ( 7 ) 4 . 4 ( 2 ) *
C 1 1 3 1 . 1 2 8 ( 1 ) 0 . 0 7 5 ( 1 ) 0 . 2 2 4 3 ( 8 ) 5 . 7 ( 3 ) *
C114 1 . 0 9 6 ( 1 ) - 0 . 0 1 5 ( 1 ) 0 . 1 4 8 2 ( 9 ) 6 . 8 ( 3 ) *
C 1 1 5 0 . 9 8 2 ( 1 ) - 0 . 0 7 2 ( 1 ) 0 . 1 1 6 ( 1 ) 7 . 8 ( 4 ) *
C 1 1 6 0 . 8 9 1 ( 1 ) - 0 . 0 2 8 ( 1 ) 0 . 1 6 5 0 ( 8 ) 5 . 9 ( 3 ) *
C 1 1 7 0 . 7 8 0 7 ( 8 ) 0 . 0 5 0 7 ( 8 ) 0 . 3 9 5 5 ( 6 ) 3 . 3 ( 2 ) *
C 1 1 8 0 . 6 8 6 3 ( 9 ) 0 . 0 6 4 3 ( 9 ) 0 . 4 4 8 7 ( 7 ) 4 . 0 ( 2 ) *
C 1 1 9 0 . 6 6 1 8 ( 9 ) 0 . 0 0 6 6 ( 9 ) 0 . 5 1 7 8 ( 7 ) 4 . 7 ( 2 ) *
C120 0 . 7 3 1 6 ( 9 ) - 0 . 0 6 5 9 ( 9 ) 0 . 5 3 3 1 ( 7 ) 4 . 8 ( 2 ) *
C 1 2 1 0 . 8 2 5 4 ( 9 ) - 0 . 0 7 9 1 (9 ) 0 . 4 8 2 2 (7 ) 4 . 4 ( 2 ) *
C122 0 . 8 5 2 5 ( 8 ) - 0 . 0 2 0 8 ( 8 ) 0 . 4 1 3 9 ( 6 ) 3 . 7 ( 2 ) *
TABLE I I : C o n t i n u e d .
24
A t o m X y z B ( A 2 )
C 2 1 1 0 . 6 9 8 8 ( 8 ) 0 . 5 9 6 1 ( 8 ) 0 . 2 1 6 5 ( 6 ) 2 . 9 ( 2 ) *
C 2 1 2 0 . 6 6 3 3 ( 9 ) 0 . 6 7 2 6 ( 9 ) 0 . 2 8 9 0 ( 7 ) 4 . 6 ( 2 ) *
C 2 1 3 0 . 5 9 1 ( 1 ) 0 . 7 4 5 ( 1 ) 0 . 2 7 3 6 ( 8 ) 5 . 3 ( 3 ) *
C214 0 . 5 5 8 ( 1 ) 0 . 7 3 8 ( 1 ) 0 . 1 8 3 6 ( 8 ) 5 . 7 ( 3 ) *
C 2 1 5 0 . 5 9 2 ( 1 ) 0 . 6 6 2 ( 1 ) 0 . 1 1 2 0 ( 8 ) 6 . 2 ( 3 ) *
C 2 1 6 0 . 6 6 4 2 ( 9 ) 0 . 5 9 0 ( 1 ) 0 . 1 2 7 4 ( 7 ) 4 . 8 ( 2 ) *
C 2 1 7 0 . 9 4 3 4 ( 8 ) 0 . 5 9 6 7 ( 8 ) 0 . 2 3 6 1 ( 6 ) 3 . 5 ( 2 ) *
C 2 1 8 0 . 9 9 3 ( 1 ) 0 . 7 0 1 ( 1 ) 0 . 3 0 3 5 ( 8 ) 5 . 5 ( 3 ) *
C 2 1 9 1 . 1 0 9 ( 1 ) 0 . 7 7 3 ( 1 ) 0 . 2 9 5 4 (9 ) 6 . 9 ( 3 ) *
C220 1 . 1 6 8 ( 1 ) 0 . 7 3 9 ( 1 ) 0 . 2 2 6 ( 1 ) 7 . 5 ( 3 ) *
C 2 2 1 1 . 1 2 4 ( 1 ) 0 . 6 4 1 ( 1 ) 0 . 1 5 6 ( 1 ) 9 . 3 ( 4 ) *
C 2 2 2 1 . 0 0 4 ( 1 ) 0 . 5 6 6 ( 1 ) 0 . 1 5 9 8 ( 9 ) 7 . 3 ( 3 ) *
H18 0 . 4 5 1 2 0 . 1 6 1 2 0 . 0 9 3 7 4 *
H19 0 . 2 7 4 1 0 . 1 8 7 6 0 . 0 4 1 0 5 *
H20 0 . 2 0 5 5 0 . 3 5 0 6 0 . 1 1 6 6 6 *
H 2 1 0 . 3 0 6 4 0 . 4 8 3 3 0 . 2 5 1 7 6 *
H22 0 . 4 8 6 5 0 . 4 6 3 0 0 . 3 0 4 7 4*
H112 1 . 0 6 1 4 0 . 1 8 0 9 0 . 3 3 0 5 5 *
H 1 1 3 1 . 2 0 9 7 0 . 1 1 0 0 0 . 2 4 5 0 7 *
H114 1 . 1 5 7 3 - 0 . 0 4 0 4 0 . 1 1 4 2 8 *
H 1 1 5 0 . 9 6 2 3 - 0 . 1 3 8 7 0 . 0 6 2 1 1 0 *
H116 0 . 8 0 8 8 - 0 . 0 6 5 9 0 . 1 4 3 5 7 *
TABLE II: Continued.
25
Atom X y z B(A2)
H118 0.6379 0.1136 0.4376 5*
H119 0.5972 0.0167 0.5544 6*
H120 0.7137 -0.1068 0.5796 6 *
H121 0.8729 -0.1289 0.4936 5*
H122 0.9194 -0.0290 0.3795 4*
H212 0.6878 0.6767 0.3502 5*
H213 0.5650 0.7970 0 . 3237 6*
H214 0.5101 0.7877 0.1720 7*
H215 0.5673 0.6580 0.0507 8*
H216 0.6891 0.5373 0.0769 6*
H218 0.9509 0.7254 0.3554 7*
H219 1.1429 0.8466 0.3414 8*
H220 1.2476 0.7864 0.2248 9*
H221 1.1693 0.6196 0.1055 12*
H222 0.9682 0.4973 0.1099 9 *
Starred atoms were refined isotropically. Anisotropically refined atoms are given in the form of the isotropic equivalent displacement parameter defined as: (4/3)* [a2*B(l,l) + b2*B(2,2) + c2*B(3,3) + ab(cos gamma)*B(l,2) + ac(cos beta)*B(i,3) + bc(cos alpha)*B(2,3)]
26
Figure 6. ORTEP diagram of Cluster 3 with the thermal ellipsoids drawn at 50% probability level. Phenyl groups and hydrogen atoms omitted for clarity. Structure determined by Professor S.G. Bott, University of North Texas.
27
thioanhydride and the /x2-phosphido ligands. Selected bond
distances and angles are given in Table III and Table IV
respectively. If one compares the bond distances between
the tricobalt core in cluster 3 with the bond distances of
the tricobalt core of the parent PhCCo3(CO)9 cluster (2.47
A ) one finds a difference of 0.10 A . Examining the bond
distances in cluster 3 between the Co3-C16, and the C0I-CI6
atoms, with the C16 atom being the apical carbon, one finds
no real differences when compared to cobalt-apical carbon
bond distances in the PhCCo3(CO)9 cluster. The bond
distances between the Co3 core in cluster 3 with the axial
and equatorial CO's is nearly the same as that of the
PhCCo3(CO)9 cluster (1.79 A on average). The only real
notable difference is on the Col atom, which shows the Co-
CO(ax) and Co-CO(eq) bond distances to be 0.05 A shorter on
the average. The bond angles of cluster 3, specifically
the Co3-Cl6-Cl7, Col-Cl6-Cl7, and Col-Cl6-Co3 angles are
all smaller in comparison to the parent cluster
PhCCo3(C0)9. For example, the Col-Cl6-Co3 bond angle is
6.2° smaller than the observed 81° in the PhCCo3(CO)9
cluster.
III. Cyclic Voltammetric Studies of Cluster 3.
Cyclic voltammetric studies were carried out at a
platinum electrode in dichloromethane containing a 0.25 M
tetra-n-butylammonium perchlorate (TBAP) as the supporting
electrolyte. The CV of 3 at room temperature Figure 7
28
TABLE III: Selected Bond Distances ( A ) of Cluster 3 with Estimated Standard Deviations in Parentheses.
Atom 1 Atom 2 Distance Atom 1 Atom 2 Distance
Col Co2 2.578(1) P2 C217 l.812(9)
Col Co3 2.402(2) 01 CI 1.15(1)
Col PI 2.139(3) 02 C2 1.16(1)
Col CI 1.752(9) 03 C3 1.14(1)
Col C2 1.74(1) 04 C4 1.16(1)
Col C16 1.93(1) 05 C5 1.14(1)
Co2 Co3 2.671(2) 06 C6 1.14(1)
Co2 PI 2.264(3) 012 C12 1.190(9)
Co2 C3 1.791(9) 014 C14 1.19(1)
Co2 C4 1.78(1) Cll C12 1.47(1)
Co2 Cll 2.050(9) Cll C15 1.46(1)
Co2 C15 2.130(9) C14 C15 1.50(1)
Co3 P2 2.213(2) C15 C16 1.44(1)
Co3 C5 1.79(1) C16 C17 1.48(1)
Co3 C6 1.80(1) C17 C18 1.39(1)
Co3 C16 2.028(9) C17 C22 1.40(1)
S C12 1.816(9) C18 C19 1.38 (2)
S C14 1.787(7) C19 C2 0 1.36(2)
PI c m 1.81(1) C2 0 C21 1.36(1)
PI C117 1.82(1) C21 C22 1.38(2)
P2 Cll 1.814(9) c m C112 1.39(1)
P2 C211 1.83(1) c m C116 1.37(1)
TABLE III: Continued.
29
Atom l Atom 2 Distance Atom 1 Atom 2 Distance
C112
C113
C114
C115
C117
C117
C118
C119
C120
C121
C211
C18
C19
C20
C21
C22
C112
C113
C114
C115
C116
C118
C113
C114
C115
C116
C118
C122
C119
C120
C121
C122
C212
H18
H19
H20
H21
H22
H112
H113
H114
H115
H116
H118
1.40 (2)
1.32(1)
1.34(2)
1.42(2)
1.38(1)
1.40(2)
1.38(2)
1.38(2)
1.36(2)
1.38(2)
1.37(1)
0 . 95
0 . 95
0.95
0.95
0 . 95
0 .95
0 . 95
0 . 95
0.95
0 . 95
0 .95
C211
C212
C213
C214
C215
C217
C217
C218
C219
C220
C221
C121
C122
C212
C213
C214
C215
C216
C218
C219
C220
C221
C216
C213
C214
C215
C216
C218
C222
C219
C220
C221
C222
H121
H122
H212
H213
H214
H215
H216
H218
H219
H220
H221
1.38(1)
1.40 (2)
1.39(2)
1.35(2)
1.40(2)
1.36(1)
1.37(2)
1.41(2)
1.29(2)
1.33(2)
1.45(2)
0.95
0 . 95
0 .95
0.95
0.95
0 . 95
0 . 95
0 .95
0 . 95
0 . 95
0 .95
30
Atom l Atom 2 Distance
C222 H222 0.95
TABLE III: Continued.
Atom l Atom 2 Distance
C119 H119 0.95
C120 H120 0.95
31
TABLE IV: Selected Bond Angles (deg)of Cluster 3 with Estimated Standard Deviations in Parentheses.
Atom l
Atom 2
Atom 3
Angle Atom 1
Atom 2
Atom 3
Angle
Co2 Col Co3 64.77 (5) Co3 Co2 C3 92.9(3)
Co2 Col PI 56.45(7) Co3 Co2 C4 171.3(3)
Co2 Col CI 132.8(3) Co3 Co2 Cll 75.1(2)
Co2 col C2 122.3 (3) Co3 Co2 C15 68.2(2)
Co2 Col C16 76.7(2) PI Co2 C3 101.0(3)
Co3 COl PI 101.84(8) PI Co2 C4 91.0(3)
Co3 Col CI 148.0(4) PI Co2 Cll 151.6(2)
Co3 Col C2 71.4 (3) PI Co2 C15 111.1(2)
Co3 Col C16 54.6 (3) C3 Co2 C4 95.1(4)
PI Col CI 110.0(4) C3 Co2 Cll 104.3(4)
PI Col C2 101.0(4) C3 Co2 C15 142.4(4)
PI COl C16 133.1(2) C4 Co2 Cll 99.5(4)
CI COl C2 104.1(4) C4 Co2 C15 103.2(4)
CI Col C16 99.4(4) Cll Co2 C15 40.8(3)
C2 Col C16 106.3(5) Col Co3 Co2 60.81(5)
Col Co2 Co3 54.42(4) Col Co3 P2 121.68(9)
Col Co2 PI 51.95(7) Col Co3 C5 115.5(3)
Col Co2 C3 131.2 (3) Col Co3 C6 109.3(4)
Col Co2 C4 121.2 (3) COl Co3 C16 50.7(3)
Col Co2 Cll 100.7(2) Co2 Co3 P2 74.45(8)
Col Co2 C15 63.9(2) Co2 Co3 C5 172.6(3)
TABLE IV: Continued.
32
Atom l
Atom 2
Atom 3
Angle Atom 1
Atom 2
Atom 3
Angle
Co3 Co2 PI 90.90(8) Co2 Co3 C6 92.3(3)
Co2 Co3 C16 73 . 0(3) Co2 C3 03 176.3(7)
P2 Co3 C5 104.0(3) Co2 C4 04 176.1(8)
P2 Co3 C6 107 . 8(3) Co3 C5 05 178(1)
P2 Co3 C16 83.0(2) Co3 C6 06 176.3(8)
C5 Co3 C6 95.1(4) Co2 Cll P2 100.6(4)
C5 Co3 C16 99.7(4) Co2 Cll C12 113.5(7)
C6 Co3 C16 159.0(5) Co2 Cll C15 72.5(5)
C12 S C14 93.7(4) P2 Cll C12 131.4(6)
Col PI Co2 71.61(9) P2 Cll C15 107.7(5)
Col PI Clll 126.2 (3) C12 Cll C15 114.6(7)
Col PI C117 120.7(3) S C12 012 120.4(7)
Co2 PI Clll 115.7(3) S C12 Cll 109.4(5)
Co2 PI C117 117.1(3) 012 C12 Cll 130.2(8)
c m PI C117 103.3(5) S C14 014 121.9(7)
Co3 P2 Cll 92.4(3) S C14 C15 110.5(5)
Co3 P2 C211 120.9(2) 014 C14 C15 127.7(7)
Co3 P2 C217 119.2(3) Co2 C15 Cll 66.7(5)
Cll P2 C211 106.9(4) Co2 C15 C14 113.0(6)
Cll P2 C217 114.0(4) Co2 C15 C16 103.9(6)
C211 P2 C217 103.0(4) Cll C15 C14 111.8(6)
TABLE I V : C o n t i n u e d .
33
A t o m l
A t o m 2
A t o m 3
A n g l e A t o m 1
A t o m 2
A t o m 3
A n g l e
C o l C I 0 1 1 7 4 . 0 ( 9 ) C l l C15 C16 1 2 1 . 7 ( 8 )
C o l C2 0 2 1 6 8 . 1 ( 9 ) C14 C15 C16 1 2 3 . 5 ( 7 )
COl C16 Co3 7 4 . 8 ( 3 ) P I C 1 1 7 C 1 1 8 117 .7 (8 )
C o l C16 C15 9 6 . 0 ( 6 ) P I C 1 1 7 C 1 2 2 123 .3 (7 )
C o l C16 C17 1 2 8 . 3 ( 5 ) C 1 1 8 C 1 1 7 C 1 2 2 1 1 9 ( 1 )
Co3 C16 C15 1 0 2 . 6 ( 5 ) C 1 1 7 C 1 1 8 C 1 1 9 1 2 0 . (1)
Co3 C16 C17 1 2 4 . 0 ( 6 ) C 1 1 8 C 1 1 9 C 1 2 0 1 2 0 . (1)
C15 C16 C17 1 2 0 . 4 ( 7 ) C 1 1 9 C120 C 1 2 1 1 2 1 . (1)
C16 C17 C18 1 2 1 . 6 ( 8 ) C 1 2 0 C 1 2 1 C 1 2 2 1 2 1 . (1)
C16 C17 C22 1 2 0 . 7 ( 7 ) C 1 1 7 C 1 2 2 C 1 2 1 119 .7 (9 )
C18 C17 C22 1 1 7 . 5 ( 8 ) P2 C 2 1 1 C 2 1 2 120 .4 (8 )
C17 C18 C19 1 2 0 . 2 ( 9 ) P2 C 2 1 1 C 2 1 6 119 .4 (7 )
C18 C19 C20 1 2 1 . 0 ( 8 ) C 2 1 2 C 2 1 1 C 2 1 6 1 2 0 . (1)
C19 C20 C 2 1 1 2 0 . (1 ) C 2 1 1 C 2 1 2 C 2 1 3 1 2 0 ( 1 )
C20 C 2 1 C22 1 2 0 . ( 1 ) C 2 1 2 C 2 1 3 C 2 1 4 1 1 9 . ( 1 )
C17 C22 C 2 1 1 2 1 . 3 ( 7 ) C 2 1 3 C 2 1 4 C 2 1 5 1 2 1 . (1)
P I c m C 1 1 2 1 2 2 . 8 ( 7 ) C 2 1 4 C 2 1 5 C 2 1 6 1 2 0 . (1)
P I c m C 1 1 6 1 1 8 . 5 ( 7 ) C 2 1 1 C 2 1 6 C 2 1 5 1 1 9 ( 1 )
C112 c m C 1 1 6 1 1 8 . 7 ( 9 ) P2 C 2 1 7 C 2 1 8 123 .1 (8 )
c m C 1 1 2 C 1 1 3 1 1 9 . 6 ( 8 ) P2 C 2 1 7 C 2 2 2 117 .4 (7 )
C112 C 1 1 3 C 1 1 4 1 2 0 . ( 1 ) C 2 1 8 C 2 1 7 C 2 2 2 119 .2 (9 )
TABLE IV: Continued.
34
Atom 1
Atom 2
Atom 3
Angle Atom 1
Atom 2
Atom 3
Angle
C I 13 C114 C 1 1 5 1 2 4 . ( 1 ) C 2 1 7 C 2 1 8 C 2 1 9 1 1 9 . ( 1 )
C114 C 1 1 5 C 1 1 6 1 1 7 . ( 1 ) C 2 1 8 C 2 1 9 C 2 2 0 1 2 1 . (1)
c m C 1 1 6 C 1 1 5 1 2 1 ( 1 ) C 2 1 9 C220 C 2 2 1 1 2 3 . (1)
C220 C 2 2 1 C 2 2 2 1 1 8 . ( 1 ) C 2 1 7 C 2 2 2 C 2 2 1 1 1 9 . ( 1 )
C17 C18 H18 1 2 0 C 1 1 8 C 1 1 9 H 1 1 9 1 2 0
C19 C18 H18 1 2 0 C 1 2 0 C 1 1 9 H 1 1 9 1 2 0
C18 C19 H19 1 1 9 C 1 1 9 C 1 2 0 H 1 2 0 1 2 0
C2 0 C19 H19 1 1 9 C 1 2 1 C120 H 1 2 0 1 2 0
C19 C20 H2 0 1 2 0 C 1 2 0 C 1 2 1 H 1 2 1 1 2 0
C 2 1 C20 H2 0 1 2 0 C 1 2 2 C 1 2 1 H 1 2 1 1 2 0
C20 C 2 1 H 2 1 1 2 0 C 1 1 7 C 1 2 2 H 1 2 2 1 2 0
C22 C 2 1 H 2 1 1 2 0 C 1 2 1 C 1 2 2 H 1 2 2 1 2 0
C17 C22 H22 1 1 9 C 2 1 1 C 2 1 2 H 2 1 2 1 2 0
C 2 1 C22 H22 1 1 9 C 2 1 3 C 2 1 2 H 2 1 2 1 2 0
c m C 1 1 2 H 1 1 2 1 2 0 C 2 1 2 C 2 1 3 H 2 1 3 1 2 1
C 1 1 3 C 1 1 2 H 1 1 2 1 2 0 C 2 1 4 C 2 1 3 H 2 1 3 1 2 1
C112 C 1 1 3 H 1 1 3 1 2 0 C 2 1 3 C 2 1 4 H 2 1 4 1 1 9
C114 C 1 1 3 H 1 1 3 1 2 0 C 2 1 5 C 2 1 4 H 2 1 4 1 1 9
C 1 1 3 C114 H 1 1 4 1 1 8 C 2 1 4 C 2 1 5 H215 1 2 0
C 1 1 5 C114 H 1 1 4 1 1 8 C 2 1 6 C 2 1 5 H215 1 2 0
C114 C 1 1 5 H115 1 2 1 C 2 1 1 C 2 1 6 H 2 1 6 1 2 0
35
Atom Atom Atom Angle 1 2 3
C215 C216 H216 120
C217 C218 H218 120
C219 C218 H218 120
C218 C219 H219 120
C220 C219 H219 120
C222 C221 H221 121
C217 C222 H222 120
C221 C222 H222 120
TABLE IV: Continued.
Atom Atom Atom Angle 1 2 3
C116 C115 H115 121
Clll C116 H116 120
C115 C116 H116 120
C117 C118 H118 120
C119 C118 H118 120
C219 C220 H220 118
C221 C220 H220 118
C220 C221 H221 121
36
-5.000
-3.000
-1.000
1.000
3.000
5.000
7.000
9.000 1 1.600 1.200 0.800 0.400 -0.400 -0.1 - 1 . 2 0 0 - 1 . 6 0 0
E ( V )
Figure 7. Cathodic scan cyclic voltammogram of Cluster 3 in dichloromethane containing 0.25 M TBAP at v = 0.1 V/s.
37
shows a well-defined redox couple at E1/2 = -0.39 V, which
is assigned to the 0/-1 redox couple. The second reduction
at E1/2 = -1.02 V, assigned to the -1/-2 redox couple, is
not as well defined. Based on the cathodic and anodic peak
current ratios (ipc/ipa) being near unity at all scan rates
measured and the linear relationship between the square
root of the scan rate and the current function, it can be
said that both reduction processes are reversible and
diffusion controlled27. An irreversible oxidation is also
observed and assigned to the 0/+1 redox couple. The peak
current ratios (ipa/ipc) deviate largely from unity and are
not readily discernable at the scan rates examined. A
closer examination of the CV at low temperatures still
proves the oxidation to be an irreversible process27. The
diffusion coefficient of 3 has been determined from the
slope of the plot of ip vs v1/2 using the Randies-Sevcik
equation34 {ip = (2.69 x 10s) n3/2AD1/2Cv1/2} where ip is peak
current, n is the electron stoichiometry, A is the
electrode area (cm2) , D is the diffusion coefficient
(cm2/s), C is concentration (mol/cm3) , and v is the scan
rate (v/s). Cluster 3 has diffusion coefficient value of
3.45 x l0"6cm2/s. If one compares this value with other
cobalt clusters of this nature24,25, for example,
PhCCo3 (CO) 7 (cis - Ph2PCH=CHPPh2)27 (D = 3.34 x l0"6cm2/s) one
finds close agreement.
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38
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