Rhenium carbonyl complexes containing bridging SiPh3 and SiPh2 ligands

Article abstract of DOI:10.1021/om0504304

The reaction of Re₂(CO)₈[μ-C(H)C(H)Bu ⁿ](μ-H) (1) with Ph₃SiH at 97 °C has yielded the three new compounds Re(CO)₅(SiPh₃) (5), Re ₂(CO)₆(μ-η⁷-SiPh₃)(μ-H) (6), and Re₂(CO)₈(μ-SiPh₂)(SiPh ₃)(μ-H) (7) in 13, 10, and 30% yields, respectively. Compound 5 consists of a single rhenium atom with five carbonyl ligands and a terminal SiPh₃ ligand. Compound 6 contains two rhenium atoms with a bridging SiPh₃ ligand in which the silicon atom is bonded to one rhenium atom and one phenyl ring is η⁶-coordinated to the other rhenium atom. A hydrido ligand bridges the Re-Re bond. Compound 7 contains a Re ₂(CO)₈ group with one bridging SiPh₂ ligand and one terminal SiPh₃ ligand. A hydrido ligand bridges one of the Re - Si bonds of the bridging SiPh₂ ligand. The reaction of 1 with Ph ₃SiH at 125 °C yielded 5 and 6 and a new product, Re ₂(CO)₈(μ-SiPh₂)₂ (8), which contains two bridging SiPh₂ ligands, one on each side of the Re-Re single bond. Compound 7 is a precursor to 8. Compound 7 was converted into 8 at 125 °C via the elimination of benzene. All four new compounds were characterized by IR and ¹H NMR spectroscopy and by single-crystal X-ray diffraction analysis.

Full text of DOI:10.1021/om0504304

Organometallics 2005, 24, 4489-4493
4489
Rhenium Carbonyl Complexes Containing Bridging
SiPh3 and SiPh2 Ligands
Richard D. Adams* and Jack L. Smith, Jr.
Department of Chemistry and Biochemistry, University of South Carolina,
Columbia, South Carolina 29208
Received May 30, 2005
The reaction of Re2(CO)8[µ-C(H)C(H)Bun](µ-H) (1) with Ph3SiH at 97 °C has yielded the
three new compounds Re(CO)5(SiPh3) (5), Re2(CO)6(µ-η7-SiPh3)(µ-H) (6), and Re2(CO)8(µ-
SiPh2)(SiPh3)(µ-H) (7) in 13, 10, and 30% yields, respectively. Compound 5 consists of a single
rhenium atom with five carbonyl ligands and a terminal SiPh3 ligand. Compound 6 contains
two rhenium atoms with a bridging SiPh3 ligand in which the silicon atom is bonded to one
rhenium atom and one phenyl ring is η6-coordinated to the other rhenium atom. A hydrido
ligand bridges the Re-Re bond. Compound 7 contains a Re2(CO)8 group with one bridging
SiPh2 ligand and one terminal SiPh3 ligand. A hydrido ligand bridges one of the Re-Si bonds
of the bridging SiPh2 ligand. The reaction of 1 with Ph3SiH at 125 °C yielded 5 and 6 and
a new product, Re2(CO)8(µ-SiPh2)2 (8), which contains two bridging SiPh2 ligands, one on
each side of the Re-Re single bond. Compound 7 is a precursor to 8. Compound 7 was
converted into 8 at 125 °C via the elimination of benzene. All four new compounds were
characterized by IR and 1H NMR spectroscopy and by single-crystal X-ray diffraction analysis.
Introduction
ligand; see eq 3.2 As a result, we decided to investigate
the reaction of 1 with Ph3SiH.
In recent studies we have found that the complex Re2-
(CO)8[µ-C(H)C(H)Bun](µ-H) (1) reacts with Ph3SnH to
yield the complex Re2(CO)8(µ-SnPh2)2 (2), which con-
tains two Re(CO)4 groups linked by two bridging SnPh2
ligands and an unusually long Re-Re bond; see eq 1.1
Palladium tri-tert-butylphosphine groups can be added
to two of the four Re-Sn bonds in 2 to yield the bis-
Pd(PBut3) adduct, Re2(CO)8(µ-SnPh2)2[Pd(PBut3)]2 (3),
see eq 2.
The activation of Si-H bonds by metal atoms is
central to the catalytic processes known as hydrosilyl-
ation.3 Polynuclear metal complexes themselves have
shown potential for serving as hydrosilylation catalysts.4
Consequently, the synthesis and characterization of
metal complexes containing silicon is key to understand-
ing the mechanism of these catalytic processes. Metal-
silyl and -siloxyl complexes have been reported for
almost every transition metal.5
We have obtained four new complexes containing
rhenium-silicon bondssRe(CO)5(SiPh3) (5), Re2(CO)6-
(2) Adams, R. D.; Cortopassi, J. E.; Yamamoto, J. H. Organometallics
1993, 12, 3036.
(3) (a) Speier, J. L. Adv. Organomet. Chem. 1979, 17, 407. (b) Chalk,
A. J.; Harrod, J. F. J. Am. Chem. Soc. 1965, 87, 16. (c) Comprehensive
Handbook on Hydrosilylation; Marciniec, B. M., Ed.; Pergamon
Press: Oxford, 1992. (d) Marciniec, B.; Gulinski, J. J. Organomet.
Chem. 1993, 446, 15. (e) Ojima, I. In The Chemistry of Organic Silicon
Compounds; Patai, S., Rappaport, Z., Eds.; Wiley: Chichester, England,
1989; Chapter 25, pp 1479-1526. (f) Ojima, I.; Kogure, T. Rev. Silicon,
Germanium, Tin, Lead Compd. 1981, 5, 7-66.
A few years ago, we reported that 1 reacts with HSi-
(OMe)3 at 97 °C to give the compound Re2(CO)8[µ-η3-
Si(OMe)3](µ-H) (4), containing a bridging trimethoxysilyl
(4) (a) Adams, R. D.; Barnard, T. S.; Li, Z.; Wu, W.; Yamamoto, J.
H. Organometallics 1998, 17, 2567. (b) Ojima, I.; Donovan, R. J.; Clos,
N. Organometallics 1991, 10, 2606. (c) Ojima, I.; Ingallina, P.; Donovan,
R. J.; Clos, N. Organometallics 1991, 10, 38. (d) Matsuda, I.; Ogiso,
A.; Sato, S.; Izumi, Y. J. Am. Chem. Soc. 1989, 111, 2332.
(5) Corey, J. Y.; Braddock-Wilking, J. Chem. Rev. 1999, 99, 175.
* To whom correspondence should be addressed. E-mail:
Adams@mail.chem.sc.edu.
(1) Adams, R. D.; Captain, B.; Johansson, M.; Smith, J. L., Jr. J.
Am. Chem. Soc. 2005, 127, 489.
10.1021/om0504304 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 08/02/2005

4490 Organometallics, Vol. 24, No. 18, 2005
Adams and Smith
(µ-η7-SiPh3)(µ-H) (6), Re2(CO)8(µ-SiPh2)(SiPh3)(µ-H) (7),
and Re2(CO)8(µ-SiPh2)2 (8)sfrom the reaction of 1 with
Ph3SiH. Each of the products was characterized struc-
turally by a single-crystal X-ray diffraction analysis.
These results are reported herein.
Table 1. Crystallographic Data for Compounds 5
and 6
5
6
empirical formula
fw
ReSiO5C23H15
585.64
Re2SiO6C24H16‚C6H6
878.97
cryst syst
lattice params
a (Å)
triclinic
orthorhombic
Experimental Section
11.0932(12)
12.4543(13)
16.1824(17)
86.041(2)
80.139(2)
89.981(2)
2197.3(4)
P1h
9.7639(4)
16.9418(7)
17.9854(8)
90
90
90
2975.1(2)
P212121
4
1.962
8.210
b (Å)
General Data. All reactions were performed under a
nitrogen atmosphere. Reagent grade solvents were dried by
the standard procedures and were freshly distilled prior to use.
Infrared spectra were recorded on a Thermo-Nicolet Avatar
360 FT-IR spectrophotometer. 1H NMR spectra were recorded
at room temperature on a Varian Mercury spectrometer
operating at 300.1 MHz. Elemental analyses were performed
by Desert Analytics (Tucson, AZ). Product separations were
performed by TLC in air on Analtech 0.25 and 0.5 mm silica
gel 60 Å F254 glass plates. Re2(CO)10 was obtained from Strem
Chemicals, Inc. Ph3SiH was purchased from Aldrich and used
as received. Re2(CO)8[µ-C(H)C(H)Bun](µ-H) (1) was prepared
by a previously reported procedure.6
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
space group
Z-value
4
F
calc (g cm-3
)
1.770
µ(Mo KR) (mm-1
temperature (K)
2θmax (deg)
)
5.615
296(2)
296(2)
50.04
50.06
no. of observations
no. of params
goodness of fit
max. shift in cycle
residuals:a R1;
wR2 (I > 2σ(I))
abs corr
6817
5100
541
356
1.082
1.054
0.006
0.003
Reaction of 1 with Ph3SiH at 97 °C. Ph3SiH (144 mg,
0.55 mmol) was added to a solution of 1 (75 mg, 0.11 mmol) in
30 mL of heptane. The reaction mixture was heated to reflux
for 5 h. After cooling, the solvent was removed in vacuo. The
products were separated by TLC using a 3:1 hexane/CH2Cl2
solvent mixture to yield, in order of elution, 8.6 mg (13% yield)
of colorless Re(CO)5(SiPh3) (5), 33.9 mg (30% yield) of colorless
Re2(CO)8(µ-SiPh2)(SiPh3)(µ-H) (7), and 8.4 mg (10% yield) of
Re2(CO)6(µ-η7-SiPh3)(µ-H) (6). Spectral data for 5: IR νCO (cm-1
in hexane): 2118 (w), 2012 (s), 2002 (m). 1H NMR (CD2Cl2 in
ppm): δ 7.51 (m, 6 H, Ph), 7.32 (m, 9 H, Ph). Anal. Calc: 47.17
C, 2.58 H. Found: 47.08 C, 2.83 H. Spectral data for 6: IR
νCO (cm-1 in hexane): 2078 (m), 1999 (s), 1990 (m), 1979 (s),
1947 (m). 1H NMR (CD2Cl2 in ppm): δ 7.78 (m, 4 H, Ph), 7.38
(m, 6 H, Ph), 6.01 (t, 2 H, Ph), 5.71 (t, 1 H, Ph), 5.28 (d, 2 H,
Ph), -18.45 (s, 1 H, µ-H). MS (e/z): 800 (M+), 772 (M - CO),
744 (M - 2CO), 716 (M - 3CO), 688 (M - 4CO), 660 (M -
5CO), 632 (M - 6CO), 554 (M - 6CO - Ph). Anal. Calc: 35.99
C, 2.01 H. Found: 36.39 C, 2.30 H. Spectral data for 7: IR
νCO (cm-1 in hexane): 2106 (m), 2062 (w), 2024 (m), 2012 (vs),
2005 (w), 1991 (m), 1973 (m). 1H NMR (CD2Cl2 in ppm): δ
7.60 (m, 6 H, Ph), 7.47 (m, 4 H, Ph), 7.36 (m, 15 H, Ph), -9.43
0.0625; 0.1795
0.0179; 0.0445
SADABS
1.000/0.533
5.228
SADABS
0.194/0.076
0.784
max./min.
largest peak (e Å-3
)
a R1 ) ∑hkl(||Fobs| - |Fcalc||)/∑hkl|Fobs|; wR2 ) [∑hklw(|Fobs| -
|Fcalc|)2/∑hklwF2
]
1/2; w ) 1/σ2(Fobs); GOF ) [∑hklw(|Fobs| - |Fcalc|)2/
obs
.
(ndata - nvari)]1/2
0.71073 Å). The raw data frames were integrated with the
SAINT+ program7 by using a narrow-frame integration algo-
rithm. Corrections for Lorentz and polarization effects were
also applied with SAINT+. An empirical absorption correction
based on the multiple measurement of equivalent reflections
was applied using the program SADABS. All structures were
solved by a combination of direct methods and difference
Fourier syntheses and refined by full-matrix least-squares on
F2 using the SHELXTL software package.8 All non-hydrogen
atoms in the main residue were refined with anisotropic
thermal parameters. All phenyl hydrogen atoms were placed
in geometrically idealized positions and included as standard
riding atoms during the least-squares refinements. The hy-
drido ligands were located and structurally refined. Crystal
data, data collection parameters, and results of the analyses
are listed in Tables 1 and 2.
Compound 5 crystallized in the triclinic crystal system. The
space group P1h was assumed and confirmed by the successful
solution and refinement of the structure. Compound 6 crystal-
lized in the orthorhombic crystal system. The space group
P212121 was identified uniquely on the basis of the systematic
absences in the intensity data. One molecule of benzene
cocrystallized with the complex and was successfully located
and refined with anisotropic thermal parameters with 8
geometric restraints. Compounds 7 and 8 crystallized in the
monoclinic crystal system. For 7 the space group P21/c was
identified uniquely on the basis of the systematic absences in
the intensity data. For 8 the space groups C2, Cm, and C2/m
were indicated by the systematic absences in the data. The
last space group was selected initially and confirmed by the
successful solution and refinement of the structure.
1
(s, 1 H, µ-H, JSi-H ) 44 Hz). Anal. Calc: 43.92 C, 2.52 H.
Found: 43.75 C, 2.71 H.
Reaction of 1 with Ph3SiH at 125 °C. Ph3SiH (144 mg,
0.55 mmol) was added to a solution of 1 (75 mg, 0.11 mmol) in
30 mL of octane. The reaction mixture was heated to reflux
for 12 h. Upon cooling to room temperature, a yellow precipi-
tate formed, which was collected by filtration and recrystallized
from hexane/CH2Cl2 to give 46.5 mg (44% yield) of Re2(CO)8-
(µ-SiPh2)2 (8). The mother liquor was dried in vacuo and
separated by TLC using a 3:1 hexane/CH2Cl2 solvent mixture
to yield, in order of elution, 15.8 mg (25% yield) of 5 and 4.9
mg (6% yield) of 6. No 7 was obtained. Spectral data for 8: IR
1
νCO (cm-1 in CH2Cl2): 2068 (m), 2010 (s), 1985 (m). H NMR
(CD2Cl2 in ppm): δ 7.67 (m, 8 H, Ph), 7.40 (m, 12 H, Ph). Anal.
Calc: 39.99 C, 2.10 H. Found: 39.60 C, 2.02 H.
Conversion of 7 to 8. A solution of 7 (6.1 mg, 0.0059 mmol)
in 10 mL of octane was heated to reflux for 8 h. Workup as
described above provided 4.7 mg (84% yield) of 8.
Crystallographic Analyses. Colorless crystals of 5 and 7
suitable for X-ray diffraction analyses were grown by slow
evaporation of a hexane/CH2Cl2 solvent mixture at 5 °C. Yellow
crystals of 6 and 8 were grown from benzene/octane at 5 °C.
Each data crystal was glued onto the end of a thin glass fiber.
X-ray intensity data were measured by using a Bruker SMART
APEX CCD-based diffractometer using Mo KR radiation (λ )
Results and Discussion
The reaction of 1 with Ph3SiH at 97 °C yielded three
new Re-Si complexes, Re(CO)5(SiPh3) (5), Re2(CO)6(µ-
(7) SAINT+, version 6.2a; Bruker Analytical X-ray Systems, Inc.:
Madison, WI, 2001.
(8) Sheldrick, G. M. SHELXTL, version 6.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1997.
(6) Nubel, P. O.; Brown, T. L. J. Am. Chem. Soc. 1984, 106, 644.

Rhenium Carbonyl Complexes
Organometallics, Vol. 24, No. 18, 2005 4491
Table 2. Crystallographic Data for Compounds 7
and 8
7
8
empirical formula
fw
Re2Si2O8C38H26
1039.17
Re2Si2O8C32H20
961.06
cryst syst
lattice parameters
a (Å)
monoclinic
monoclinic
13.6837(6)
10.6083(5)
24.8274(11)
90
93.638(1)
90
14.0667(11)
10.6056(8)
12.0970(10)
90
117.384(1)
90
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
3596.7(3)
P21/c
1602.5(2)
C2/m
space group
Z-value
4
2
F
calc (g cm-3
)
1.919
1.992
µ(Mo KR) (mm-1
temperature (K)
2θmax (deg)
)
6.843
7.671
296(2)
50.06
296(2)
50.04
Figure 2. ORTEP diagram of the molecular structure of
Re2(CO)6(µ-η7-SiPh3)(µ-H) (6) showing 40% thermal el-
lipsoid probability. Selected intramolecular distances (Å)
and angles (deg): Re(1)-Re(2) ) 3.2192(2), Re(1)-Si(1) )
2.5175(11), Si(1)-C(31) ) 1.905(4), Re(1)-H(1) ) 1.894-
(10), Re(2)-H(1) ) 1.897(10), Re(2)-Re(1)-Si(1) ) 74.91-
(2).
no. of observations
no. of params
goodness of fit
max. shift in cycle
residuals:a R1;
wR2 (I > 2σ(I))
abs corr
5674
1464
455
124
1.04
1.078
0.002
0.001
0.0207; 0.0478
0.0132; 0.0328
SADABS
0.710/0.452
0.861
SADABS
0.541/0.434
0.356
max./min.
largest peak (e Å-3
)
η7-SiPh3 ligand where the silicon atom is η1-coordinated
to one rhenium atom and one of the phenyl groups is
η6-coordinated to the other rhenium atom. This type of
coordination is very rare, but one example was observed
previously in the compound Cp*FeCr(CO)3(µ-SiMe2)(µ-
η7-SiPhMe2).10 The two rhenium atoms are linked by a
long Re-Re single bond [3.2712(2) Å]. The unusual
length of the Re-Re bond may be due to the presence
of a bridging hydride ligand that was located and refined
[Re(1)-H(1) ) 1.894(10) Å, Re(2)-H(1) ) 1.897(10) Å,
δ ) -18.45]. The Re-Re distance in Re2(CO)10 is 3.042-
(1) Å.11 The Re-Si distance [2.5175(11) Å] in 6 is quite
short in comparison to that observed for 5 and may be
related to the coordination of one of the phenyl rings to
the neighboring rhenium atom.
a R1 ) ∑hkl(||Fobs| - |Fcalc||)/∑hkl|Fobs|; wR2 ) [∑hklw(|Fobs| -
|Fcalc|)2/∑hklwF2
]
obs
1/2; w ) 1/σ2(Fobs); GOF ) [∑hklw(|Fobs| - |Fcalc|)2/
(ndata - nvari)]1/2
.
An ORTEP diagram of the molecular structure of
compound 7 is shown in Figure 3. Selected intramo-
lecular bond distances and angles are listed in Table 3.
The structure of 7 consists of a central Re2(CO)8 group
containing a SiPh2 ligand that bridges the Re-Re bond
and a terminal SiPh3 ligand that is bonded solely to Re-
(2). As in 6, the Re-Re bond in 7 is also quite long
[3.1486(2) Å]. The hydrido ligand H(1) was located
crystallographically and was actually found to bridge
the Re(1)-Si(1) bond, although it seems to be more
strongly bonded to the rhenium atom than to the silicon
atom [Re(1)-H(1) ) 1.67(4) Å; Si(1)-H(1) ) 1.73(4) Å].
Figure 1. ORTEP diagram of the molecular structure of
Re(CO)5(SiPh3) (5) showing 40% thermal ellipsoid prob-
ability. Re(1)-Si(1) ) 2.617(4) Å.
η7-SiPh3)(µ-H) (6), and Re2(CO)8(µ-SiPh2)(SiPh3)(µ-H)
(7), in 13, 10, and 30% yields, respectively. All com-
1
pounds were characterized by IR, H NMR, elemental,
and single-crystal X-ray diffraction analyses. Compound
5 contains a single rhenium atom with five carbonyl
ligands and one terminally coordinated SiPh3 ligand.
An ORTEP diagram of the molecular structure of 5 is
shown in Figure 1. The molecule has no unusual or
unexpected bond distances or angles. The Re-Si dis-
tance [2.617(4) Å] is similar to that found in the related
compound Re(CO)5SiMe3 [Re-Si ) 2.600(1) Å].9
1
The resonance for this ligand was observed in the H
NMR spectrum of 7 at -9.43 ppm. The existence of a
significant Si-H interaction was confirmed by large
coupling between the silicon atom, 29Si, and hydrogen
An ORTEP diagram of the molecular structure of 6
is given in Figure 2. This compound contains a bridging
(10) Pannell, K. H.; Sharma, H. K.; Kapoor, R. N.; Cervantes-Lee,
F. J. Am. Chem. Soc. 1997, 119, 9315.
(11) Churchill, M. R.; Amoh, K. N.; Wasserman, H. J. Inorg. Chem.
1981, 20, 1609.
(9) Couldwell, M. C.; Simpson, J.; Robinson, W. T. J. Organomet.
Chem. 1976, 107, 323.

4492 Organometallics, Vol. 24, No. 18, 2005
Adams and Smith
Figure 4. ORTEP diagram of the molecular structure of
Re2(CO)8(µ-SiPh2)2 (8) showing 40% thermal ellipsoid prob-
ability.
compound Re2(CO)8(µ-SiPh2)(µ-H)2 (9) was proposed to
have two hydride ligands, one bridging each of the two
Re-Si bonds in the molecule. The Re-Si distances in 9
are 2.544(9) Å in length.15 Curiously, Cowie et al.
concluded that the hydride ligands in 9 and in the
related compounds Re2(CO)7(µ-SiEt2)2(µ-H)2 and Re2-
(CO)6(µ-SiEt2)2(µ-H)4 were “bonded terminally to the
rhenium atoms with no attractive interactions to the
silicon atoms”, even though the hydride ligands were
not located crystallographically.16 On the basis of the
high-quality structural analysis and the observation of
large NMR coupling between the 29Si and H, we are
quite confident that there are significant interactions
between the silicon atom and the hydrido ligand in 7.
Similar Si-H interactions probably exist in 9 also.
Figure 3. ORTEP diagram of the molecular structure of
Re2(CO)8(SiPh3)(µ-SiPh2)(µ-H) (7) showing 40% thermal
ellipsoid probability.
Table 3. Selected Intramolecular Distances and
Angles for Compounds 7 and 8a
compound 7
compound 8
Bond Distances (Å)
Re(1)-Re(2)
Re(1)-Si(1)
Re(2)-Si(1)
Re(2)-Si(2)
Re(1)-H(1)
Si(1)-H(1)
C-O (av)
3.1486(2) Re(1)-Si(1)
2.5792(9) Re(1)-Re(1)*b
2.5041(10) C-O (av)
2.5901(9)
2.5633(8)
3.0180(3)
1.137(5)
1.67(4)
1.73(4)
1.13(1)
Bond Angles (deg)
Si(1)-Re(1)-Re(2) 50.66(2)
Re(1)-Si(1)-Re(1)* 72.13(3)
Si(1)-Re(2)-Si(2) 150.56(3) Si(1)-Re(1)-Si(1)* 107.87(3)
Si(1)-Re(2)-Re(1) 52.81(2)
Si(1)-Re(1)-Re(1)* 53.935(14)
Si(2)-Re(2)-Re(1) 156.34(2) Re-C-O (av)
Re(2)-Si(1)-Re(1) 76.53(3)
177.4(3)
Re-C-O (av)
176(1)
a Estimated standard deviations in the least significant figure
are given in parentheses. b *Indicates an atom related by inversion
symmetry.
Compound 7 was converted to Re2(CO)8(µ-SiPh2)2 (8)
in 84% yield via the thermal elimination of benzene
1
(confirmed by H NMR spectroscopy) at 125 °C, see eq
1
29Si-H
atom, J
) 44 Hz. This value is slightly smaller
4.
than the Si-H coupling observed for the hydrogen atom
bridging the Mn-Si bond in the compounds (C5H4Me)-
1
29
Mn(CO)2(H)SiR3, SiR3 ) SiPh3, SiHPhNp ( J Si-H ) 65
and 69 Hz, respectively).12 Schubert has concluded that
no strong Si-H interaction is to be expected if J(SiMH)
drops below 10-20 Hz.13 The Si-H distance is slightly
longer than that found for Si-H bonds engaged in
agostic interactions with transition metal atoms,5 but
is much shorter than the 2.00 Å designated by Schubert
as the upper limit for significant Si-H bonding interac-
tions.13 The Si-H distance in 7 is very similar to the
Si-H bond distance of 1.70(3) Å found for the hydrogen
atom bridging the Ru-Si bond in the compound (C5-
Me5)Ru[P(C6H11)3](CPh2SiH).14 The bond lengthening
effect usually found associated with bridging hydrido
ligands is observed in 7 as well, as the Re(1)-Si(1) bond
distance [2.5792(9) Å] is significantly longer than the
unbridged Re(2)-Si(1) bond distance [2.5041(10) Å]. The
Compound 8 can also be obtained in 44% yield directly
from the reaction of 1 with Ph3SiH at 125 °C. An
ORTEP diagram of the molecular structure of 8 is given
in Figure 4. Selected intramolecular distances and
angles are listed in Table 3. Compound 8 contains 2/m
symmetry in the solid state. The molecule has two SiPh2
ligands that bridge the two Re(CO)4 groups, and it is
isostructural with our previously reported dirhenium-
ditin compound, 2.1 In earlier studies,1,17 we have
observed that the addition of bridging SnPh2 and GePh2
ligands can result in the elongation of the M-M bond
to which they were associated. However, this trend was
not observed for 8, and, in fact, the Re-Re bond distance
(12) Colomer, E.; Corriu, R. J. P.; Marzin, C.; Vioux, A. Inorg. Chem.
1982, 21, 368.
(13) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151.
(14) Yin, J.; Klosin, J.; Abboud, K. A.; Jones, W. M. J. Am. Chem.
Soc. 1995, 117, 3298.
(15) Elder, M. Inorg. Chem. 1970, 9, 762.
(16) Cowie, M.; Bennett, M. J Inorg. Chem. 1977, 16, 2325.
(17) Adams, R. D.; Captain, B.; Smith, J. L., Jr., Hall, M. B.; Beddie,
C. L.; Webster, C. E. Inorg. Chem. 2004, 43, 7576.

Rhenium Carbonyl Complexes
Organometallics, Vol. 24, No. 18, 2005 4493
in 8 [3.0180(3) Å] is much shorter than that in 2 [3.1902-
(4) Å],1 and even shorter than in Re2(CO)10 [3.042(1)
Å].11 The manganese homologue of 7 was reported by
Dahl a number of years ago, and it too has a relatively
short Mn-Mn distance [2.871(2) Å].18
provide an explanation for the formation of 8 from 1.
This may be relevant to the formation of 2 as well.
Compounds 5 and 6 seem to be unrelated to the
formation of 7 and 8. In previous work we showed that
1 reacts with HSi(OMe)3 to yield compound 4, which
contains a bridging trimethoxysilyl ligand, eq 3.6 The
formation of the unusual η7-bridging SiPh3 ligand in 6
shows that this reaction can be extended to silyl groups
bearing phenyl rings.
Concluding Remarks
These new compounds further expand and clarify the
nature of the additions and bonding of silyl and silylene
groups to dirhenium carbonyl complexes. The reaction
of 1 with Ph3SiH at 97 °C yielded a monorhenium
complex 5 and two dirhenium complexes 6 and 7. At
125 °C, this same reaction yielded 5 and 6 as well as
the new dirhenium compound 8. Compound 7 was
shown to be a precursor to 8 (see eq 4), which helps to
Acknowledgment. This research was supported by
the Office of Basic Energy Sciences of the U.S. Depart-
ment of Energy under Grant No. DE-FG02-00ER14980.
Supporting Information Available: CIF files are avail-
able for each of the structural analyses. This material is
available free of charge via the Internet at http://pubs.acs.org.
(18) Simon, G. L.; Dahl, L. F. J. Am. Chem. Soc. 1973, 95, 783.
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