New alkyne bridged mixed-metal clusters and studies of their activity for catalytic hydrosilylation of alkynes

Article abstract of DOI:10.1016/S0022-328X(00)00302-8

The homologous series of compounds MPt₂(CO)₅(PPh₃)₂(PhC₂Ph), M=Fe (1), M=Ru (3) and M=Os (4) were obtained in the yields 55%, 24% and 30% from the reactions of Pt(PPh₃)₂(PhC

Full text of DOI:10.1016/S0022-328X(00)00302-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 614–615 (2000) 75–82
New alkyne bridged mixed-metal clusters and studies of their
activity for catalytic hydrosilylation of alkynes
Richard D. Adams *, Uwe Bunz, Burjor Captain, Wei Fu, Winfred Steffen
Department of Chemistry and Biochemistry, Uni6ersity of South Carolina, Columbia, SC 29208, USA
Received 26 January 2000; accepted 25 May 2000
Dedicated to Professor Sheldon G. Shore on the occasion of his 70th birthday.
Abstract
The homologous series of compounds MPt2(CO)5(PPh3)2(PhC2Ph), M=Fe (1), M=Ru (3) and M=Os (4) were obtained in
the yields 55%, 24% and 30% from the reactions of Pt(PPh3)2(PhC2Ph) with Fe(CO)5, Ru3(CO)10, and Os(CO)5, respectively. Each
of the products was characterized by IR, elemental analysis and a single crystal X-ray diffraction analysis. A second mixed-metal
cluster product, Ru2Pt(CO)7(PPh3)2(PhC2Ph) (2) (45% yield) was also obtained from the reaction that yielded 3. In fact, it is
obtained in a higher yield than that of 3. Compounds 1, 3, and 4 are isostructural and are comprised of a MPt2 (M=Fe, Ru or
Os) triangular metal cluster containing a triply bridging diphenylacetylene ligand. The structure of compound 2 is similar to that
of 1, 3, and 4, but contains two ruthenium and one platinum atom in the triangular cluster. One coproduct
Os(CO)2(PPh3)2(PhC2Ph) (5) (25% yield) was obtained from the reaction of Os(CO)5 with Pt(PPh3)2(PhC2Ph). Compound 5
contains only one metal atom with an approximately trigonal bipyramidal coordination having the two phosphine ligands in the
axial positions and the alkyne in an equatorial site. The reaction of 2 with H2 in refluxing hexane afforded the tetranuclear
complex H2Ru2Pt2(CO)8(PPh3)2 (6) (11% yield) that contains an Ru2Pt2 tetrahedral shaped cluster with two bridging hydride
ligands. The ability of the solutions of compounds 1–6 and Pt(PPh3)2(PhC2Ph) to produce catalytic hydrosilylation of
diphenylacetylene by triethylsilane to yield (E)-[(1,2-diphenyl)ethenyl]triethylsilane at 30°C, and 1,4-bis(trimethylsilyl)butadiyne
with triethylsilane to yield (E)-2-triethylsilyl-1,4-bis(trimethylsilyl)-1-buten-3-yne at 60°C was investigated. Pt(PPh3)2(PhC2Ph) was
the best catalyst for these reactions. Compound 5 is completely inactive. A combination of evidence suggests that the catalytic
activity exhibited by the mixed-metal cluster complexes is produced principally by fragmentation products which are almost
certainly mononuclear platinum complexes. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Platinum; Ruthenium; Alkyne; Cluster; Hydrosilylation; Catalysis
1. Introduction
Metal cluster complexes have been considered as frag-
ments of a metal surface surrounded by a layer of
‘adsorbed’ ligand molecules [4], and the ‘cluster/surface’
analogy was proposed in the late 1970s to show the
connections between cluster chemistry to heterogeneous
catalysis [5].
We have recently reported that the layer segregated
platinum/ruthenium cluster complex Pt3Ru6(CO)20(m3-
PhC2Ph)H2 exhibits good catalytic activity for the hy-
drosilylation of alkynes under homogeneous conditions
[6], however a study of the catalytic hydrosilylation of
alkenes by Ru3(CO)12 has indicated cluster fragmenta-
tion processes are important in this case [7].
Mixed-metal heterogeneous catalysts have attracted
much interest because their catalytic properties are
often superior to that of their components [1]. Various
mechanisms of cooperativity have been proposed. For
example, it has been suggested that a metal atom can
activate its neighbor simply through the donation of
electron density [2]. It has also been proposed that the
different metals may exhibit bifunctional cooperativity
such that one metal performs one role in a catalytic
reaction and the other performs a second function [3].
Here we report the synthesis and characterization of
the new heteronuclear three metal cluster complexes
MPt2(CO)5(PPh3)2(PhC2Ph) where M=Fe (1), Ru (3),
* Corresponding author. Tel.: +1-803-777-7187; fax: +1-803-777-
6781.
E-mail address: adams@psc.sc.edu (R.D. Adams).
0022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00302-8

76
R.D. Adams et al. / Journal of Organometallic Chemistry 614–615 (2000) 75–82
Os (4) that were obtained from the reactions of
Pt(PPh3)2(PhC2Ph) with Fe(CO)5, Ru3(CO)12 and
Os(CO)5, respectively. Coproducts Ru2Pt(CO)7(PPh3)-
(PhC2Ph) (2) and Os(CO)2(PPh3)2(PhC2Ph) (5) that
were also obtained from the ruthenium and osmium
reactions were fully characterized. In addition, the reac-
tion of compound 2 with H2 in a refluxing hexane
solution yielded the new tetranuclear cluster complex
H2Ru2Pt2(CO)8(PPh3)2 (6). The ability of compounds
1–6 and the mononuclear complex Pt(PPh3)2(PhC2Ph)
to produce catalytic hydrosilylation of dipheny-
lacetylene by triethylsilane to yield (E)-[(1,2-diphenyl)-
2.3. Reaction of Ru3(CO)12 with Pt(PPh3)2(PhC2Ph)
A 105.0-mg amount of Ru3(CO)12 (0.165 mmol) and
150.0 mg of Pt(PPh3)2(PhC2Ph) (0.167 mmol) were
dissolved in 15 ml of toluene in a 25 ml three-neck
round-bottom flask equipped with a stir bar at 25°C.
Immediately, the color of the solution turned dark red.
The reaction mixture was then heated to reflux for 30
min. After cooling, the solvent was removed in vacuo,
and the products were separated by TLC using a 3:1
hexane–methylene chloride solvent mixture. The com-
pounds eluted in the following order were: Ru3(CO)12
(yellow, trace); Ru4(CO)12(PhC2Ph) [10] (brown, 1.8
mg, 1%); Ru3(CO)11(PPh3) [11] (orange, 30.2 mg, 21%);
Ru3(CO)7(PPh2)2(m-C6H5) [12] (red, trace); Ru3(CO)8(m-
ethenyl]triethylsilane,
and
1,4-bis(trimethylsilyl)-
butadiyne with triethylsilane to yield (E)-2-triethylsilyl-
1,4-bis(trimethylsilyl)-1-buten-3-yne were also investi-
gated and are reported here. The evidence indicates that
fragmentation processes are probably important and
may involve mononuclear platinum complexes as the
true catalysts.
C4Ph4)
[13]
(orange–yellow,
trace);
Ru2Pt-
(CO)7(PPh3)2(PhC2Ph) (dark red–brown, 76.8 mg,
45%) (2); Ru3(CO)10(PPh3)2 [14] (red, 7.0 mg, 4%);
RuPt2(CO)5(PPh3)2(PhC2Ph) (orange–yellow, 53.0 mg,
24%) (3). Spectral data for 2: IR wCO (cm−1 in hexane):
2068 (s), 2034 (m, sh), 2029 (vs), 1992 (m), 1980 (m),
1964 (m). Anal. Calc.: C, 42.94; H, 2.43. Found: C,
42.60; H, 2.44%. Spectral data for 3: IR wCO (cm−1 in
CH2Cl2): 2045 (s), 2011 (s), 1961 (m). 31P-NMR (d8-tol-
uene): l=17.64 ppm; 1JP–Pt=3417 Hz; 2JP–Pt=168
Hz. Anal. Calc.: C, 49.47; H, 3.00. Found: C, 49.56; H,
3.00%.
2. Experimental
2.1. General data
All reactions were performed under a nitrogen atmo-
sphere. Reagent grade solvents were dried by the stan-
dard procedures and were freshly distilled prior to use.
Infrared spectra were recorded on a Nicolet 5DXBO
FTIR spectrophotometer. 1H-NMR and 31P-NMR
were recorded on a Varian Inova 400 spectrometer
operating at 399.9 and 161.9 MHz, respectively. Ele-
mental analyses were performed by Oneida Research
Services (Whitesboro, NY, USA) and Desert Analytics
(Tucson, AZ, USA). Fe(CO)5 and Ru3(CO)12 were pur-
chased from Aldrich and Strem, respectively, and were
used without further purification. Pt(PPh3)2(PhC2Ph)[8]
and Os(CO)5[9] were prepared according to the pub-
lished procedures. Product separations were performed
by TLC in air on Analtech 0.25 and 0.5 mm silica gel
2.4. Reaction of Os(CO)5 with Pt(PPh3)2(PhC2Ph)
A 80.0-mg amount of Pt(PPh3)2(PhC2Ph) (0.089
mmol) dissolved in 5 ml of toluene was added to a 50
ml three-neck round-bottom flask containing a 30 ml
solution of Os(CO)5 in hexane (ca. 2 mg ml−1). The
reaction mixture was heated to reflux and stirred for 1
h, after which the volatiles were removed in vacuo. The
products were separated by TLC using a 3:1 hexane–
methylene chloride solvent mixture to yield 21.0 mg
(25%) of Os(CO)2(PPh3)2(PhC2Ph) (5), and 38.5 mg
(30%) of OsPt2(CO)5(PPh3)2(PhC2Ph) (4). Spectral data
for 4: IR wCO (cm−1 in CH2Cl2): 2047 (s), 2011 (s), 1952
(m). Anal. Calc.: C, 46.41; H, 2.83. Found: C, 46.07; H,
2.63%. Spectral data for 5: IR wCO (cm−1 in CH2Cl2):
1958 (s), 1892 (vs). Anal. Calc.: C, 65.81; H, 4.24.
Found: C, 65.41; H, 3.84%.
,
60 A F254 glass plates.
2.2. Reaction of Fe(CO)5 with Pt(PPh3)2(PhC2Ph)
A 67.0-mg amount of Pt(PPh3)2(PhC2Ph) (0.074
mmol) was dissolved in 10 ml of toluene in a 25 ml
three-neck round-bottom flask. A 12.7-ml amount of
Fe(CO)5 (0.097 mmol) were added via syringe, and the
reaction mixture was then heated to reflux for 45 min.
After cooling, the solvent was then removed in vacuo,
and the product was purified by TLC using a 1:1
hexane–methylene chloride solvent mixture to yield
53.0 mg (55%) of an orange product, FePt2(CO)5-
(PPh3)2(PhC2Ph) (1). Spectral data for 1: IR wCO (cm−1
in CH2Cl2): 2041 (s), 2012 (m, sh), 1989 (s), 1930 (m,
br). Anal. Calc.: C, 51.25; H, 3.13. Found: C, 51.51; H,
3.18%.
2.5. Reaction of 2 with H2
A 42.0-mg amount of 2 was dissolved in 40 ml of
hexane in a 100 ml three-neck round-bottom flask
equipped with a stir bar, reflux condenser, and gas
inlet. The solution was then heated to reflux and purged
with hydrogen (1 atm) for 1 h. After the solvent was
removed the reaction mixture was transferred to TLC
plates and separated by using a 3:1 hexane–methylene
chloride solvent mixture to yield 6.0 mg of

R.D. Adams et al. / Journal of Organometallic Chemistry 614–615 (2000) 75–82
77
H4Ru4(CO)11(PPh3) [15,16] (18% yield) and 5.6 mg of
H2Ru2Pt2(CO)8(PPh3)2 (6) (11% yield). Spectral data
for 6: IR wCO (cm−1 in hexane): 2082 (w), 2060 (s), 2032
on the basis of systematic absences observed during the
collection of the intensity data. The structure was
solved by a combination of direct methods (SIR92) and
difference Fourier syntheses. All non-hydrogen atoms
were refined with anisotropic thermal parameters. In
the final stages of the analysis, one equivalent of meth-
ylene chloride from the crystallization solvent was
found co-crystallized in the crystal lattice. This
molecule was included in the crystal structure analysis
and was refined satisfactorily.
1
(vs) 2009 (m, sh), 1989 (s), 1957 (m). H-NMR (CDCl3
in ppm): l=7.22–7.40 (m, 30H, Ph), l= −8.21 (d,
2
1
2H, m-H, JP–H=21 Hz, JPt–H=289 Hz). Anal. Calc.:
C, 39.35; H, 2.40. Found: C, 40.61; H, 2.74%.
2.6. Crystallographic analysis
Orange crystals of 1, dark red–brown crystals of 2,
orange–yellow crystals of 3, yellow crystals of 4 and 5,
and dark red crystals of 6 suitable for diffraction
analysis were grown by slow evaporation of solvent
from solutions in hexane–methylene chloride solvent
mixtures at 25°C. All crystals used for the diffraction
measurements were mounted in thin-walled glass capil-
laries. Diffraction measurements were made on a
Rigaku AFC6S fully automated four-circle diffractome-
ter using graphite-monochromated Mo–Ka radiation.
The unit cells of the crystals were determined and
refined from 15 randomly selected reflections obtained
by using the AFC6 automatic search, center, index, and
least squares routines. All data processing was per-
formed on a Silicon-Graphics INDIGO [2] workstation
by using the TEXSAN structure solving program library
obtained from the Molecular Structure, The Wood-
lands, TX, USA. Neutral atom scattering factors were
calculated by the standard procedures [17]. Anomalous
dispersion corrections were applied to all non-hydrogen
atoms [18]. Lorentz/polarization (Lp) corrections were
applied to the data for each structure. Full-matrix
least-squares refinements minimized the function:
Compound 5 crystallized in the triclinic crystal sys-
(
tem. The space group P1 was assumed and confirmed
by the successful solution and refinement of the struc-
ture. The structure was solved by a combination of
direct methods (SIR92) and difference Fourier synthe-
ses. All non-hydrogen atoms were refined with an-
isotropic thermal parameters.
Compound 6 crystallized in the monoclinic crystal
system. The space group P21/c was identified uniquely
on the basis of the systematic absences observed during
the collection of the intensity data. The structure was
solved by a combination of direct methods (SIR92) and
difference fourier syntheses. All non-hydrogen atoms
were refined with anisotropic thermal parameters. The
two hydride ligands were located and refined. In the
final stages of the analysis, one equivalent of hexane
from the crystallization solvent was found co-crystal-
lized in the crystal lattice. The molecule was included in
the crystal structure analysis and was refined satisfacto-
rily. Crystallographic data for compounds 1–6 are
listed in Tables 1 and 2.
2.7. General procedures for the catalysis studies
ꢀ
hkl w(ꢁFoꢁ−ꢁFcꢁ)2, where w=1/|2(F), |(F)=|(F2o)/
2Fo and |(F2o)=[|(Iraw)2+(0.08Inet)2]1/2/Lp.
All reactions were performed under a nitrogen atmo-
sphere. Diphenylacetylene, triethylsilane, and d8-toluene
were purchased from Aldrich and were used without
further purification. 1,4-bis(trimethylsilyl)butadiyne was
purchased from Aldrich and was recrystallized using
hexane prior to use. CDCl3 solvent was purchased from
Cambridge Isotope Laboratories and used as received.
C6Me6 purchased from Aldrich was used as an internal
calibration for determining the amounts of product for
the hydrosilylation of diphenylacetylene reaction.
Turnover frequencies (TOF) were obtained by measur-
Compounds 1, 3, and 4 are isomorphous and crystal-
lized in the orthorhombic crystal system. The space
group Pbca was established on the basis of the system-
atic absences observed during the collection of the
intensity data. The structures were solved by a combi-
nation of direct methods (SIR92) and difference Fourier
syntheses. For compound 1, all non-hydrogen atoms in
the structures were refined with anisotropic thermal
parameters. For compounds 3 and 4, all atoms in the
structure except for the carbon atoms on the
triphenylphosphine ligand and the hydrogen atoms,
were refined with anisotropic thermal parameters. Each
compound crystallized with one equivalent of hexane in
the crystal lattice. It was located and refined in the
analyses of 1 and 3. In 4 it was located, partially refined
and then fixed on the final cycles because it would not
refine to convergence. For all three structural analyses,
the hydrogen atoms were calculated and included as
fixed contributions to the scattering.
1
ing the product formed by H-NMR spectroscopy.
2.8. Catalytic hydrosilations of diphenylacetylene
In a typical run a 2.9-mg amount of 1 (0.00225
mmol), 40-mg amount of PhC2Ph (0.225 mmol), and
10-mg amount of C6Me6 was all dissolved in 1.5 ml of
CDCl3 in a 5 ml round-bottom flask equipped with a
stir bar. The solution was stirred to ensure that all of
the complex had dissolved completely. Two portions of
0.6 ml of this solution were then transferred via syringe
Compound 2 crystallized in the monoclinic crystal
system. The space group P21/c was identified uniquely

78
R.D. Adams et al. / Journal of Organometallic Chemistry 614–615 (2000) 75–82
to two clean sealed 5 mm NMR tubes. To each of these
tubes 144 ml of Et3SiH (0.9 mmol, 1000 equivalents to
1) was added. The NMR tubes were then evacuated
and filled with nitrogen three times, after which they
were placed in an oil bath maintained at a temperature
of 30°C for 1 h. 1H-NMR spectra of the reaction
mixture showed that 2.0% of PhC2Ph was converted to
(E)-[(1,2-diphenyl)ethenyl]triethylsilane [19]. Similarly
Table 1
Crystallographic data for diffraction studies
Compound
1
3
4
Empirical formula
Formula weight
Crystal system
Pt2FeP2O5C55H40 · C6H14
1375.07
Orthorhombic
Pt2RuP2O5C55H40 · C6H14
1420.29
Orthorhombic
Pt2OsP2O5C55H40 · C6H14
1509.42
Orthorhombic
Lattice parameters
,
a (A)
21.407(2)
19.973(7)
24.029(4)
10 274(35)
Pbca (no. 61)
8
21.422(3)
19.839(3)
24.115(5)
10 248(2)
Pbca (no. 61)
8
21.408(6)
19.848(5)
24.135(9)
10 255(4)
Pbca (no. 61)
8
,
b (A)
,
c (A)
V (A )
3
,
Space group
Z value
zcalc (g cm−3
)
1.78
58.0
1.84
58.3
1.96
80.0
v (Mo–Ka) (cm-1)
Temperature (°C)
20
20
20
2[max (°)
40.0
42.0
40.0
No. of observations (I\3|(I))
No. of variables
3124
576
1.32
0.04
3464
431
1.56
0.02
3385
406
1.21
0.00
Goodness-of-fit (GoF) a
Max. shift in cycle
Residuals: R, Rw
Absorption correction
Transmissions coefficient, max/min
0.050, 0.064
DIFABS
1.00/0.55
1.03
0.047, 0.052
DIFABS
1.00/0.83
1.42
0.042, 0.060
DIFABS
1.00/0.42
1.51
−3
,
Largest peak in final difference map (e A
)
a R=ꢀhkl(ꢁFobsꢁ−ꢁFcalcꢁꢁ)/ꢀhklꢁFobsꢁ; Rw=[ꢀhkl w(ꢁFobsꢁ−ꢁFcalcꢁ)2/ꢀhkl wFo2bs
]
1/2, w=1/|2(Fobs); GoF=[ꢀhkl w(ꢁFobsꢁ−ꢁFcalcꢁ)2/(ndata–nvari)]1/2
.
Table 2
Crystallographic data for diffraction studies
Compound
2
5
6
Empirical formula
Formula weight
Crystal system
PtRu2PO7C39H25 · CH2Cl2
1118.76
Monoclinic
OsP2O2C52H40
949.03
Triclinic
Pt2Ru2P2O8C44H32 · C6H14
1343.00
Monoclinic
Lattice parameters
,
a (A)
12.813(2)
19.791(3)
17.022(6)
90
110.96(1)
90
4031(2)
P21/c (no. 14)
4
12.298(4)
15.627(4)
11.205(2)
98.41(2)
92.49(2)
77.34(2)
2078(1)
11.156(1)
16.345(4)
28.577(5)
90
99.11(1)
90
5145(1)
P21/c (no. 14)
4
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
(
Space group
Z value
P1 (no. 2)
2
zcalc (g cm−3
)
1.84
44.1
1.52
31.8
1.73
60.9
v (Mo–Ka) (cm−1
)
No. of obsevations (I\3|(I))
No. of variables
3493
479
1.25
0.00
3653
514
1.00
0.00
3627
531
1.03
0.02
Goodness-of-fit (GoF) a
Max. shift in cycle
Residuals*: R, Rw
Absorption correction
Transmission coefficient, max/min
0.026, 0.029
DIFABS
1.00/0.66
0.52
0.029, 0.035
DIFABS
1.00/0.76
0.50
0.030, 0.040
DIFABS
1.00/0.65
0.54
−3
,
Largest peak in final difference map (e A
)
a R=ꢀhkl(ꢁꢁFobsꢁ−ꢁFcalcꢁꢁ)/ꢀhklꢁFobsꢁ; Rw=[ꢀhkl w(ꢁFobsꢁ−ꢁFcalcꢁ)2/ꢀhkl wFo2bs
]
1/2, w=1/|2(Fobs); GoF=[ꢀhkl w(ꢁFobsꢁ−ꢁFcalcꢁ)2/(ndata–nvari)]1/2
.

R.D. Adams et al. / Journal of Organometallic Chemistry 614–615 (2000) 75–82
79
a 347-ml amount of Et3SiH (2.17 mmol) was then added
to the reaction flask. The reaction flask was then evacu-
ated and filled with nitrogen three times. The flask was
then placed in an oil bath maintained at a temperature
1
of 60°C for 7 h. A H-NMR spectrum of the reaction
mixture showed that 100% of 1,4-bis(trimethylsi-
lyl)butadiyne was converted to (E)-2-triethylsilyl-1,4-
bis(trimethylsilyl)-1-buten-3-yne [20]. Similarly 2.9 mg
of
bis(trimethylsilyl)butadiyne to (E)-2-triethylsilyl-1,4-
bis(trimethylsilyl)-1-buten-3-yne, and 3.1 mg of
3
(0.00217 mmol) converted 100% of 1,4-
4
(0.00217 mmol) converted 100% of 1,4-bis(trimethylsi-
lyl)butadiyne to (E)-2-triethylsilyl-1,4-bis(trimethylsi-
lyl)-1-buten-3-yne under the same conditions.
Fig. 1. An ORTEP diagram representing the molecular structures of
compounds 1, 3, and 4 (M=Fe, Ru and Os).
3.0 mg of 3 (0.00225 mmol) converted 16.1% of PhC2Ph
to (E)-[(1,2-diphenyl)ethenyl]triethylsilane, and 3.2 mg
of 4 (0.00225 mmol) converted 8.0% of PhC2Ph to
(E)-[(1,2-diphenyl)ethenyl]triethylsilane under the same
conditions. The catalysis of compounds 2, 5, 6 and
Pt(PPh3)2(PhC2Ph) were conducted similarly.
3. Results and discussion
The
homologous
series
of
compounds
MPt2(CO)5(PPh3)2(PhC2Ph), 1, M=Fe; 3, M=Ru and
4, M=Os were obtained in the yields 55%, 24% and
30% from the reactions of Pt(PPh3)2(PhC2Ph) with
Fe(CO)5, Ru3(CO)12, and Os(CO)5, respectively. Each
of the products was characterized by IR, elemental and
a single crystal X-ray diffraction analysis. All three
compounds are isostructural and isomorphous. An OR-
TEP diagram representing the molecular structure of
these compounds is shown in Fig. 1. A listing of
selected interatomic distances and angles are given in
Table 3. Each compound consists of a triangular Pt2M
cluster with a triply bridging diphenylacetylene ligand.
In each case the Pt–Pt distance is long, Pt–Pt=
2.9. Catalytic hydrosilations of
1,4-bis(trimethylsilyl)butadiyne
2.9.1. Determination of initial rates
A 2.8-mg amount of 1 (0.00217 mmol) and a 42.0-mg
amount of 1,4-bis(trimethylsilyl)butadiyne (0.217
mmol) were all dissolved in 0.60 ml of d8-toluene in a
5-ml round-bottom flask equipped with a stir bar. The
solution was stirred until all of the 1 had dissolved
completely. Then, a 69-ml amount of Et3SiH (0.433
mmol) was added via syringe. The reaction flask was
then partially evacuated and filled with nitrogen three
times. It was then placed in a constant temperature oil
,
,
,
3.013(1) A for 1, 3.066(1) A for 3, and 3.080(1) A for 4
and can be regarded as a very weak bond or no bond
at all. The alkyne C–C bond is parallel to the Pt–Pt
,
bond and the C–C distance C(1)–C(2): 1.30(3) A for 1,
1
,
,
bath at a temperature of 60°C for 1 h. H-NMR of the
1.42(2) A for 3 and 1.39(2) A for 4, is slightly longer
,
reaction mixture showed that 4.7% of 1,4-
bis(trimethylsilyl)butadiyne was converted to (E)-2-tri-
than that found for the uncoordinated alkyne, 1.20 A,
as expected due to the effects of its coordination. The
molecular structure of these compounds is very similar
to that of the related compounds Pt2M(m3-h1:h1:h2-
PhCꢀCCꢀCPh)(CO)5(PPh3)2, M=Fe, 7 [21] and Ru, 8
[21] which were recently reported and also exhibit a
ethylsilyl-1,4-bis(trimethylsilyl)-1-buten-3-yne
[20].
Similarly, 2.9 mg of 3 (0.00217 mmol) converted 16% of
1,4-bis(trimethylsilyl)butadiyne to (E)-2-triethylsilyl-
1,4-bis(trimethylsilyl)-1-buten-3-yne, and 3.1 mg of 4
(0.00217 mmol) converted 13% of 1,4-bis(trimethylsi-
lyl)butadiyne to (E)-2-triethylsilyl-1,4-bis(trimethylsi-
lyl)-1-buten-3-yne under the same conditions. The
catalysis of compounds 2, 5, 6 and Pt(PPh3)2(PhC2Ph)
were conducted similarly.
,
long Pt–Pt distance, 2.939(2) and 3.072(1) A for the
two different crystalline forms of 7. Each platinum
atom coordinated with one triphenylphosphine ligand
and one carbonyl ligand while the heterometal atom is
coordinated with three carbonyl ligands. Assuming that
the alkyne serves as a four-electron donor, each cluster
contains a total of 46 electrons which is two electrons
less than the 48 electrons expected for a triangular
cluster where all three metal atoms obey the 18-electron
rule. Previous studies have shown that clusters contain-
ing diplatinum groups often contain fewer electrons
than that predicted by the conventional electron count-
ing theories [22].
2.9.2. Long term
In a similar manner, a 2.8-mg amount of 1 (0.00217
mmol) and a 211-mg amount of 1,4-bis(trimethylsi-
lyl)butadiyne (1.09 mmol) was all dissolved in 0.8 ml of
d8-toluene in a 5-ml round-bottom flask equipped with
a reflux condensor and a stir bar. The solution was
stirred until all of the 1 had dissolved completely. Then,

80
R.D. Adams et al. / Journal of Organometallic Chemistry 614–615 (2000) 75–82
Table 3
Selected intramolecular bond distances and angles for 1, 3 and 4
Compound 1
Compound 3
Compound 4
Atom–atom
Distance
Atom–atom
Distance
Atom–atom
Distance
a
Intramolecular bond distances
Pt(1)–Pt(2)
Pt(1)–Fe
3.013(1)
2.531(3)
2.326(6)
2.09(2)
2.608(3)
2.319(6)
2.11(2)
2.14(2)
2.14(2)
1.30(3)
Pt(1)–Pt(2)
Pt(1)–Ru
Pt(1)–P(1)
Pt(1)–C(1)
Pt(2)–Ru
Pt(2)–P(2)
Pt(2)–C(2)
Ru–C(1)
3.066(1)
2.623(2)
2.325(5)
2.04(2)
2.676(2)
2.291(5)
2.04(2)
2.25(2)
2.29(2)
1.42(2)
Pt(1)–Pt(2)
Pt(1)–Os
Pt(1)–P(1)
Pt(1)–C(1)
Pt(2)–Os
Pt(2)–P(2)
Pt(2)–C(2)
Os–C(1)
3.080(1)
2.647(1)
2.317(5)
2.09(2)
2.688(1)
2.315(6)
2.10(2)
2.26(2)
2.29(2)
1.39(2)
Pt(1)–P(1)
Pt(1)–C(1)
Pt(2)–Fe
Pt(2)–P(2)
Pt(2)–C(2)
Fe–C(1)
Fe–C(2)
C(1)–C(2)
Ru–C(2)
C(1)–C(2)
Os–C(2)
C(1)–C(2)
Atom–atom–atom
Intramolecular bond angles
Angle
Atom–atom–atom
Angle
Atom–atom–atom
Angle
b
Pt(2)–Pt(1)–Fe
Pt(1)–Pt(2)–Fe
Pt(1)–Fe–Pt(2)
55.30(7)
52.91(7)
71.79(8)
Pt(2)–Pt(1)–Ru
Pt(1)–Pt(2)–Ru–
Pt(1)–Ru–Pt(2)
55.46(4)
55.83(4)
70.71(4)
Pt(2)–Pt(1)–Os
Pt(1)–Pt(2)–Os
Pt(1)–Os–Pt(2)
55.37(3)
54.12(3)
70.51(3)
a
,
Distances are in A. Estimated S.D.s in the least significant figure are given in parentheses.
b Angles are in degrees (°). Estimated S.D.s in the least significant figure are given in parentheses.
Compound 6 was characterized by IR, elemental and
single crystal X-ray diffraction analyses, and an ORTEP
diagram of its molecular structure is shown in Fig. 4.
The molecule contains two ruthenium atoms and two
platinum atoms in a tetrahedral arrangement. The two
hydride ligands bridge two of the Ru–Pt bonds. The
electron count for the cluster is 58 which is two less
than the expected 60 electron count. However, it has
been found that platinum containing tetrahedral clus-
ters often contain 58 electrons [22].
A second mixed-metal cluster product, Ru2Pt(CO)7-
(PPh3)2(PhC2Ph) (2) (45%) was also obtained from the
reaction that yielded 3. In fact, it is obtained in a higher
yield than that of 3. Compound 2 was also character-
ized crystallographically, and an ORTEP diagram of its
structure is shown in Fig. 2. Compound 2 contains a
triangular cluster composed of one platinum and two
ruthenium atoms. The diphenylacetylene ligand is coor-
dinated as a triply bridging ligand as in 3, but the C–C
bond of the alkyne is parallel to one of the Ru–Pt
bonds. Each ruthenium atom has three carbonyl lig-
ands while the platinum atom contains the
triphenylphosphine and one carbonyl ligand. All metal
atoms have 18-electron configurations and a no unusual
metal–metal bond distances.
One coproduct Os(CO)2(PPh3)2(PhC2Ph) (5) (25%
yield) was obtained from the reaction of Os(CO)5 with
Pt(PPh3)2(PhC2Ph). Compound 5 was also character-
ized by IR, elemental and single crystal X-ray diffrac-
tion analyses. An ORTEP diagram of the molecular
structure of 5 is shown in Fig. 3. Compound 5 contains
only one metal atom. The C–C bond distance of the
,
diphenylacetylene ligand in 5 is 1.31(1) A. The coordi-
nation geometry of the osmium atom is approximately
trigonal bipyramidal with the two phosphine ligands in
the axial positions. The diphenylacetylene ligand serves
as a two electron donor and the osmium atom has an
18-electron configuration.
When a hexane solution of compound 2 was heated
to reflux in the presence of a slow purge with H2, the
new tetranuclear mixed metal cluster compound
Ru2Pt2(CO)8(PPh3)2(m-H)2 (6) was formed in 11% yield.
Fig. 2. An ORTEP diagram of Ru2Pt(CO)7(PPh3)2(PhC2Ph) (2). Se-
,
lected bond distances (A) for 2. Pt(1)–Ru(1) 2.7935(6), Pt(1)–Ru(2)
2.6584(6), Ru(1)–Ru(2) 2.6887(9), Pt(1)–C(1) 2.051(7), Ru(1)–C(2)
2.060(7), Ru(2)–C(1) 2.230(6), Ru(2)–C(2) 2.260(7), Pt(1)–P(1)
2.338(2), Pt(1)–C(10) 1.90(1), Ru(1)–C(av) 1.910(7), Ru(2)–C(av)
1.88(2), C(1)–C(2) 1.391(9).

R.D. Adams et al. / Journal of Organometallic Chemistry 614–615 (2000) 75–82
81
(1)
(2)
Solutions of compounds of 1–4, 6 and Pt(PPh3)2-
(PhC2Ph) were found to be catalytically active. Com-
pound 5 was inactive. The reactions were characterized
by ‘initial rate’ measurements by terminating the reac-
tions at the end of 1 h of reaction time. Except for the
reactions of 2, the solutions 1, 3, and 4 after catalysis
showed large amounts of the starting cluster complex
were still present (\75% by TLC separations), but
trace amounts of other metallic species were also ob-
served. Compound 2 and 6 were the best catalyst
precursors, but both also underwent greatest decompo-
sition during catalysis. The catalysis by compounds 1,
3, and 4 was further characterized by measuring for a
period of 7 h. After 7 h, all of the reactions were
complete (100% yield).
Fig. 3. An ORTEP diagram of Os(CO)2(PPh3)2(PhC2Ph) (5). Selected
,
bond distances (A) and angles (°) for 5. Os(1)–P(1) 2.384(2), Os(1)–
P(2) 2.400(2), Os(1)–C(1) 1.899(8), Os(1)–C(2) 1.903(9), Os(1)–C(3)
2.169(7), Os(1)–C(4) 2.144(7), C(3)–C(4) 1.31(1), C(1)–Os(1)–C(2)
98.0(3), C(3)–Os(1)–C(4) 35.3(3).
Significantly, in the case of the hydrosilylation of
1,4-bis(trimethylsilyl)butadiyne by 1, 3, and 4, the com-
pounds 1, 3, and 4 were recovered unchanged, and
there was no evidence for the formation of butadiyne
complexes, such as 7 and 8, from the reactions involv-
ing 1 and 3. The absence of any observable replacement
of the PhC2Ph by the 1,4-bis(trimethylsilyl)butadiyne in
the catalyses by 1 and 3 was an indication that the
diyne was not involved with the intact cluster com-
plexes. Efforts to measure the rates of catalysis as a
function of the concentration of the cluster gave poor
reproducibility, and it was suspected that cluster frag-
mentation was occurring and was possibly responsible
for the catalysis. Accordingly, the catalytic activity
of the two mononuclear complexes
5
and
Fig. 4. An ORTEP diagram of Ru2Pt2(CO)8(PPh3)2(m-H)2 (6). Selected
,
bond distances (A): Pt(1)–Pt(2) 3.137(1), Pt(1)–Ru(1) 2.711(1),
Pt(1)–Ru(2) 2.829(1), Pt(2)–Ru(1) 2.846(1), Pt(2)–Ru(2) 2.732(1),
Ru(1)–Ru(2) 2.745(1), Pt(1)–P(1) 2.322(3), Pt(2)–P(2) 2.343(3),
Pt(1)–H(2) 2.02, Pt(2)–H(1) 1.81, Ru(1)–H(1) 1.86, Ru(2)–H(2)
1.76.
Table 4
Results for the hydrosilylation of diphenylacetylene and 1,4-
bis(trimethylsilyl)butadiyne by 1, 3, and 4
Catalyst
1 TOF (h−1
)
2 TOF (h−1
)
3.1. Studies of hydrosilation catalysis of alkynes
at 30°C a
at 60°C b
Ojima [23] and Adams [6] have shown that certain
mixed metal complexes can be effective catalysts for the
hydrosilylation of alkynes. Accordingly, we have inves-
tigated the ability of compounds 1–6 and Pt(PPh3)2-
(PhC2Ph) to serve as catalyst precursors for the hy-
drosilylation of diphenylacetylene and 1,4-bis(trimethyl-
silyl)butadiyne with triethylsilane (Eqs. (1) and (2)).
Results of our investigations of these catalytic reactions
are listed in Tables 4 and 5.
FePt2(CO)5(PPh3)2(PhC2Ph)
RuPt2(CO)5(PPh3)2(PhC2Ph)
OsPt2(CO)5(PPh3)2(PhC2Ph)
Ru2Pt(CO)7(PPh3)(PhC2Ph)
Ru2Pt2(CO)8(PPh3)2H2
2.0
16
8.0
18
24
0
4.7
16
13
45
15
Os(CO)2(PPh3)2(PhC2Ph)
Pt(PPh3)2(PhC2Ph)
0
100
58
a Catalyst/alkyne/triethylsilane ratio 1/100/1000 for Eq. (1).
b Catalyst/diyne/triethylsilane ratio 1/100/200 for Eq. (2).

82
R.D. Adams et al. / Journal of Organometallic Chemistry 614–615 (2000) 75–82
Table 5
Results of the long term kinetic runs for the hydrosilylation of 1,4-bis(trimethylsilyl)butadiyne by 1, 3, and 4
Catalyst
1,4-bis(trimethylsilyl)butadiyne
Et3SiH
Time (h)
% Yield
FePt2(CO)5(PPh3)2(PhC2Ph)
RuPt2(CO)5(PPh3)2(PhC2Ph)
OsPt2(CO)5(PPh3)2(PhC2Ph)
500 equivalents
500 equivalents
500 equivalents
1000 equivalents
1000 equivalents
1000 equivalents
7
7
7
100
100
100
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The combination of evidence, strongly suggests that
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fragmentation products which are almost certainly
mononuclear platinum complexes.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 139516 for 1, 139517 for 2,
139518 for 3, 139519 for 4, 139520 for 5, 139521 for 6.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
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Acknowledgements
This research was supported by the Division of
Chemical Sciences of the Office of Basic Energy Sci-
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