Examination of metal-silicon bonding through structural and theoretical studies of an isostructural set of five-coordinate silyl complexes, Os(SiR3)Cl(CO)(PPh3)2 (R = F, Cl, OH, Me)

Article abstract of DOI:10.1021/om970580h

Os(SiCl₃)Cl(CO)(PPh₃)₂ is prepared by treatment of OsPhCl(CO)(PPh₃)₂ with excess HSiCl₃ and serves in turn as the starting material for the syntheses of three more five-coordinate süyl complexes Os(SiR₃)Cl(CO)(PPh₃)₂ (R = F, OH, Me) via substitution of the chloride groups on silicon. All four compounds were fully characterized, including a single-crystal solid-state structure of each derivative. Carbonyl stretching frequencies decrease and Os-Si bond lengths increase as R changes in the order from F to Cl to OH to Me. Ab initio calculations were performed on the model complexes Os(SiR₃)Cl(CO)(PH₃)₂ (R = F, Cl, OH, Me) to explain the trends observed in the IR and X-ray studies, and the importance of the π-acceptor capacities of the silyl groups are discussed.

Full text of DOI:10.1021/om970580h

5076
Organometallics 1997, 16, 5076-5083
Exa m in a tion of Meta l-Silicon Bon d in g th r ou gh
Str u ctu r a l a n d Th eor etica l Stu d ies of a n Isostr u ctu r a l
Set of F ive-Coor d in a te Silyl Com p lexes,
Os(SiR3)Cl(CO)(P P h 3)2 (R ) F , Cl, OH, Me)
Klaus Hu¨bler,* Patricia A. Hunt, Susan M. Maddock, Clifton E. F. Rickard,
Warren R. Roper,* David M. Salter, Peter Schwerdtfeger, and L. J ames Wright
Department of Chemistry, The University of Auckland, Private Bag 92019,
Auckland, New Zealand
Received J uly 9, 1997X
Os(SiCl3)Cl(CO)(PPh3)2 is prepared by treatment of OsPhCl(CO)(PPh3)2 with excess HSiCl3
and serves in turn as the starting material for the syntheses of three more five-coordinate
silyl complexes Os(SiR3)Cl(CO)(PPh3)2 (R ) F, OH, Me) via substitution of the chloride groups
on silicon. All four compounds were fully characterized, including a single-crystal solid-
state structure of each derivative. Carbonyl stretching frequencies decrease and Os-Si bond
lengths increase as R changes in the order from F to Cl to OH to Me. Ab initio calculations
were performed on the model complexes Os(SiR3)Cl(CO)(PH3)2 (R ) F, Cl, OH, Me) to explain
the trends observed in the IR and X-ray studies, and the importance of the π-acceptor
capacities of the silyl groups are discussed.
In tr od u ction
has its origin in the lack of general synthetic procedures.
It is not always possible to find a series of compounds,
all closely related, in which there is a systematic
variation of substituents on the silicon. The accessibil-
ity to us of a set of five-coordinate osmium-silyl
complexes where the silyl ligand changes from SiF3 to
SiCl3 to Si(OH)3 to SiMe3 prompted us to collect a
complete set of structural data from single-crystal X-ray
diffraction studies and to complement these data with
ab initio calculations. The conclusions from these
studies are reported in this paper.
A good understanding of the nature of the metal-
silicon bond is important not only from a fundamental
point of view but also for the development of successful
catalysts for the production of an increasing range of
organosilicon compounds. This understanding would
give insight into elementary steps, such as the insertion
of unsaturated molecules into M-Si bonds, which are
of central importance for many catalytic processes.
Since the first synthesis of a compound with a M-Si
bond in 1956,1 there has been debate about the elec-
tronic nature of this linkage. Early recognition that
some M-Si bond distances were conspicuously shorter
than expected led to suggestions of a dπ-dπ contribu-
tion to the bonding. However, this view finds little
current favor, and explanations involving increased
ionic character to the bonding or explanations based on
σ-effects alone (more s-character in the M-Si bond,
more p-character in the Si-substituent bond) are more
popular. A valuable photoelectron spectral study by
Lichtenberger and Rai-Chaudhuri established that the
trichlorosilyl ligand in CpFe(CO)2SiCl3 is an effective
π-acceptor.2 These authors suggest that the π-back-
bonding to SiCl3 involves significant portions of the Si-
Cl σ*-orbitals. A related study3 of Co(CO)4SiCl3,
Mn(CO)5SiCl3, and cis-Fe(CO)4(SiCl3)2 concludes that
π-acceptance is not important here, but it should be
noted that in each of these compounds all accompanying
ligands are CO, a circumstance clearly unfavorable for
π-acceptance by SiCl3.
Resu lts a n d Discu ssion
Syn th eses. The five-coordinate silyl complexes were
conveniently prepared in good yield from Os(SiCl3)Cl-
(CO)(PPh3)2 (1b) via substitution reactions involving the
chloride groups on silicon. 1b was in turn isolated as a
yellow crystalline solid by treatment of OsPhCl(CO)-
4
(PPh3)2 with excess HSiCl3 in toluene at 40 °C for 30
min, Scheme 1. An attempt to synthesize the analogous
trimethylsilyl derivative Os(SiMe3)Cl(CO)(PPh3)2 from
OsPhCl(CO)(PPh3)2 and HSiMe3 failed. Instead, the
reaction resulted in the production of the osmium(IV)
product Os(SiMe3)H3(CO)(PPh3)2.5 To obtain compound
1d , Os(SiCl3)Cl(CO)(PPh3)2 was treated with methyl-
lithium at room temperature in toluene. A color change
from yellow to red-orange occurred, and Os(SiMe3)Cl-
(CO)(PPh3)2 (1d ) was isolated as a yellow-orange solid.
A convenient route to the fluorosilyl derivative 1a
6
involved reaction of either Os[Si(OH)3]Cl(CO)(PPh3)2
or Os[Si(OEt)3]Cl(CO)(PPh3)27 with aqueous HF at room
One of the problems encountered in probing the
nature of the M-Si bond by various physical techniques
temperature for a short time. 1a is relatively unreactive
X Abstract published in Advance ACS Abstracts, October 15, 1997.
(1) Piper, T. S.; Lemal, D.; Wilkinson G. Naturwissenschaften 1956,
43 129.
(2) Lichtenberger, D. L.; Rai-Chaudhuri, A. J . Am. Chem. Soc. 1991,
113, 2923.
(4) Rickard, C. E. F.; Roper, W. R.; Taylor, G. E. J .; Waters, M.;
Wright, L. J . J . Organomet. Chem. 1990, 389, 375.
(5) Details of this compound will be reported elsewhere.
(6) Rickard, C. E. F.; Roper, W. R.; Salter, D. M.; Wright, L. J . J .
Am. Chem. Soc. 1992, 114, 9682.
(3) Novak, I.; Huang, W.; Luo, L.; Huang, H. H.; Ang, H. G.; Zybill,
C. E. Organometallics 1997, 16, 1567.
(7) Maddock, S. M. Thesis, The University of Auckland, Auckland,
New Zealand, 1995.
S0276-7333(97)00580-3 CCC: $14.00 © 1997 American Chemical Society

Os(SiR3)Cl(CO)(PPh3)2
Organometallics, Vol. 16, No. 23, 1997 5077
Ta ble 2. Cr ysta llogr a p h ic Da ta for
Os(SiR3)Cl(CO)(P P h 3)2 w ith R ) F , Cl, a n d Me
Sch em e 1
R ) F (1a )
R ) Cl (1b)
R ) CH3 (1d )
formula
C37H30ClF3OOsP2Si C38H30Cl4OOs- C40H39ClOOsP2Si
P2Si‚CH2Cl2
fw
863.29
995.55
851.39
a, pm
b, pm
c, pm
â, (deg)
V, m3
Z
1365.9(4)
1234.2(4)
2022.7(6)
97.57(3)
3380(2) × 10-30
4
1029.2(3)
1997.4(4)
1969.2(2)
91.370(10)
1162.78(8)
1879.9(2)
1697.9(3)
96.181(9)
4047(2) × 10-30 3689.9(8) × 10-30
4
4
space group P21/c
P21/n
20
71.069
1.634
3.68
0.0332
0.0829
1.053
P21/c
20
71.069
1.533
3.68
0.0335
0.0757
1.075
T, °C
λ, pm
20
71.069
F
calc, g cm-3 1.696
µ, mm-1
4.03
R (Fo)a
0.0341
0.0793
1.096
2
a
Rw (Fo
)
S
a
2
R (Fo) ) ∑||Fo|| - ||Fc||/∑|F o|. Rw (Fo2) ) {∑[w(Fo - Fc2)2]/
∑[w(Fo2)2]}1/2
.
Ta ble 1. C-O Str ech in g F r equ en cies (cm -1) for
Com p ou n d s of th e Typ e Os(SiMe3-n Rn )Cl(CO)-
(P P h 3)2 (R ) F , Cl, OH; n ) 0-3)
F
Cl
OH
SiMe3
SiMe2R
SiMeR2
SiR3
1895
19177
19337
1946
1895
19178
19288
1944
1895
19108
19178
1919
and can be recrystallized from dichloromethane/ethanol
without alcoholysis occurring.
IR Sp ectr a . The ν(CO) absorptions of solid samples
of compounds 1a and 1d were split into two bands,
which collapsed to one single peak each when the
spectra were recorded as dichloromethane solutions,
suggesting solid-state splitting. The ν(CO) values of the
isostructural set of five-coordinate silyl complexes with
the formula Os(SiMe3-nRn)Cl(CO)(PPh3)2 (R ) F,7 Cl,6,8
OH;6,8 n ) 0-3) are listed in Table 1. The ν(SiF) values
F igu r e 1. Molecular structure of Os(SiF3)Cl(CO)(PPh3)2
(1a ). All hydrogen atoms are omitted for clarity.
effects on the carbonyl stretching frequency will be
discussed in the following sections.
for compound 1a are found between 880 and 820 cm-1
,
X-r a y Str u ctu r es of Com p ou n d s 1a -d . Crystals
of Os(SiF3)Cl(CO)(PPh3)2 (1a ), Os(SiCl3)Cl(CO)(PPh3)2
(1b), and Os(SiMe3)Cl(CO)(PPh3)2 (1d ) suitable for
single-crystal X-ray structure determination were grown
from dichloromethane/ethanol, toluene/n-hexane, and
benzene/diethyl ether mixtures, respectively. Crystal
data and data collection parameters are listed in Table
2. Although the structure of Os[Si(OH)3]Cl(CO)(PPh3)2
(1c) has already been published,6 this compound will
also be discussed because of the close relationship with
the other three complexes reported here for the first
time.
The largest angles around osmium are P-Os-P
(166.55(6)°, 163.3(2)°, 165.8(1)°, 158.97(5)°) and Cl-
Os-C (167.0(2)°, 165.3(14)°, 168.9(2)°, 170.9(4)°) for
1a -d respectively, and in each case the four angles
involving Si and Os are all close to 90°. Thus, com-
pounds 1a -d all have a similar geometry which can be
described as square pyramidal with the silyl group,
which has the largest trans influence, in the apical
position. Therefore, the structure of only one of these
compounds, Os(SiF3)Cl(CO)(PPh3)2 (1a ) is depicted in
Figure 1. The difference in the orientation of the silyl
substituents with respect to the basal plane ligands in
the four structures 1a -d can be conveniently described
by the torsion angle Cl-Os-Si-Ri which has values of
5.6(3)°, -8.2(5)°, 14.4(2)°, and -2.6(3)° for the trifluo-
and ν(SiCl) for compound 1b are hidden by absorption
bands of the triphenylphosphine ligands.
Examination of Table 1 shows that sequential re-
placement of the Me groups in Os(SiMe3)Cl(CO)(PPh3)2
with either OH, Cl, or F causes the ν(CO) values to
increase. Furthermore, the magnitude of this effect
depends on the substituents in the order F > Cl > OH.
There appears to be a correlation between the elec-
tronegativity of the silyl group and the position of ν(CO).
The electronegativity of a silyl group can be estimated
by theoretical methods and is dependent upon the
substituents attached to silicon and the method used.9
For the complexes in this study, the silyl group with
the highest group electronegativity is clearly SiF3, the
SiMe3 group has the lowest electronegativity.
A shift of the carbonyl stretching frequency ν(CO) to
higher wavenumbers is usually explained by a decrease
of the electron density on the metal available for π-back-
bonding to the π*(CO)-orbitals. This decrease may be
due to an increase in the π-accepting capacity (-M) or
only due to a simple inductive σ-withdrawing effect (-I)
of the silyl group as more electronegative substituents
are placed on silicon. The importance of these two
(8) Salter, D. M. Thesis, The University of Auckland, Auckland, New
Zealand, 1993.
(9) Huheey, J . E. J . Phys. Chem. 1965, 69, 3284

5078 Organometallics, Vol. 16, No. 23, 1997
Hu¨bler et al.
Ta ble 3. Selected In ter a tom ic Dista n ces (p m ) a n d An gles (d eg) for Os(SiR3)Cl(CO)(P P h 3)2 a n d th e Mod el
Com p ou n d s Os(SiR3)Cl(CO)(P H3)2 (a -d , R ) F , Cl, OH, Me)
compound method
1a , X-ray
2a , BLYP
1b, X-ray
2b, BLYP
1c, X-ray
2c, BLYP
1d , X-ray
2d , BLYP
Os-Si
Si-Ria
225.4(2)
159.5(5)
156.7(5)
156.1(5)
240.0(2)
189.2(8)
103.1(8)
238.4(2)
237.0(2)
113.6(2)
117.9(2)
231.2
162.7
163.1
227.3(6)
206.1(10)
205.9(8)
206.9(9)
243.5(13)
187 (4)
232.0
212.0
212.9
231.9(2)
164.9(5)
164.7(5)
162.4(5)
241.9(2)
188.5(9)
100.5
238.1(1)
236.2(1)
111.3(2)
115.6(2)
237.0
164.0
167.5
237.4(2)
189.9(8)
186.6(7)
189.0(7)
244.7(4)
175.5(13)
117.1(14)
237.9(1)
236.3(1)
112.3(3)
114.9(2)
242.7
190.0
190.1
a,b
Si-Ro
Os-Clc
Os-Cc
C-Oc
247.8
186.5
121.1
245.0
248.0
186.4
121.0
245.6
249.1
185.3
122.1
244.0
250.8
185.5
121.9
243.3
104 (4)
Os-Pb
237.7(5)
240.3(5)
116.5(3)
115.7(3)
Os-Si-Ria
113.0
115.4
118.5(4)
103.6
109.8
116.1
113.9(2)
104.6
108.5
113.7
114.9(2)
105.6
108.1
113.6
a,b
Os-Si-Ro
118.0(2)
a,b
Ri-Si-Ro
99.4(3)
100.3(3)
104.8(3)
89.2(2)
103.8(9)
94.48(6)
98.93(7)
167.0(2)
166.55(6)
5.6(3)
103.1(4)
100.8(5)
99.5(4)
93.0(13)
101.6(3)
98.3(2)
102.8(3)
106.4(4)
105.9(4)
86.4(2)
104.6(1)
94.7(1)
104.9(4)
105.8(4)
103.1(4)
88.6(4)
100.46(11)
98.94(5)
102.02(5)
170.9(4)
158.97(5)
-2.6(3)
107.8
a
Ro-Si-Ro
104.5
85.8
114.3
92.4
104.3
86.4
119.3
93.7
109.0
84.6
114.9
91.4
105.7
86.7
107.9
94.1
Si-Os-Cc
Si-Os-Clc
Si-Os-Pb
98.4(2)
99.6(1)
Cl-Os-C(O)c
P-Os-P
Cl-Os-Si-Ri
159.8
170.9
0.0
165.3(14)
163.3(2)
-8.2(5)
154.3
169.2
-0.1
168.9(2)
165.8(1)
14.4(2)
160.5
169.5
0.0
165.4
168.7
0.0
a
The index i stands for in plane (Cs) and the index o for out of plane. For the X-ray structures, Ri is R2, Ro is R1 and R3 (R ) F, Cl,
b
O, C). For the X-ray data of compounds 1a -d , the bond lengths and angles for R1 and P1 are listed first, followed by the values for R3
and P2. The calculated structures have almost perfect Cs symmetry, and thus only an averaged parameter is listed. c For the disordered
structures 1b and 1d , only the parameters for the isomer analogous to the fluorine derivative depicted in Figure 1 are given.
rosilyl, trichloro, trihydroxy, and trimethyl derivatives,
respectively. While the triphenylphosphine and chlo-
ride ligands are always bent away from the silyl group
with angles considerably exceeding 90° (94.48(6)-
102.02(5)°), the Si-Os-C angle is always the smallest
from the apical silicon to any of the equatorial ligands
(86.4(2)-93.0(13)°). Disorder was found in the crystal-
lographic unit cell for the chloride and carbonyl ligands
in the complexes 1b and 1d , preventing the exact
positions of these ligands from being determined. The
structures were refined using the disorder model with
a weighting of 50% occupancy for the atoms of the Cl
and CO groups in the possible orientations. Selected
bond lengths and angles are tabulated in Table 3. For
the disordered structures 1b and 1d , only the param-
eters for the isomer analogous to the fluorine derivative
depicted in Figure 1 are given.
The Os-Cl (240.0(2)-244.7(4) pm) and Os-P bond
lengths (236.2(1)-240.3(5) pm) are very similar in all
derivatives and fall within the range observed for a
variety of osmium compounds (standard values, Os-Cl
) 238.0 pm for 393 and Os-P ) 238.4 pm for 236
observations).10 In general, the Os-Si bond becomes
shorter as groups of greater electronegativity are placed
on silicon. This phenomenon has been observed for
other transition-metal-silyl complexes. To our knowl-
edge, the Os-Si bond length of 225.4(2) pm for com-
pound 1a is the shortest Os-Si bond length so far
reported. We note that the bond lengths of 227.3(6) and
231.9(2) pm for the trichloro and trihydroxy derivatives
are shorter than that reported for a base-stabilized
osmium silylene complex, Os{dSiEt2(thf)}(thf)(TTP)
(TTP ) the dianion of tetra-p-tolylporphyrin, thf )
tetrahydrofuran), of 232.5(8) pm.11 The Os-Si distance
in the trimethylsilyl derivative 1d is 237.4(2) pm. It is
noteworthy that even this value is still much shorter
than the Os-Si single bond distance of 250 pm,12 which
is predicted from the sum of the covalent radii of Os an
Si.
The shorter Os-Si bond lengths observed when more
electronegative groups are placed on silicon would be
consistent with increasing the π-bonding from the metal
to the silyl group. This would cause π-bonding to CO
to decrease, the Os-C bond distance to lengthen, and
the CO bond to contract. Although the ν(CO) values
show the expected increase going from the trimethylsilyl
to the trifluorosilyl compound (see Table 1), a discussion
of the trends in Os-C bond lengths is complicated by
the Cl/CO disorder in compounds 1b and 1d . Since any
effects due to multiple bonding between osmium and
silicon should be most obvious for Os(SiF3)Cl(CO)(PPh3)2
(1a ) with the highly electronegative fluoro substituents
attached to silicon, the structure of 1a will be discussed
in more depth. Fortunately, the structure of 1a is not
subject to any disorder.
In addition to a very short Os-Si bond length in 1a ,
the bond angles around silicon are distorted from a
tetrahedral geometry and the average Os-Si-F bond
angle is 116.5°. The Os-Si-F2 angle of 113.6(2)° is
significantly different from the other two of 118.0(2)°
and 117.9(2)°. The average F-Si-F angle is 101.5°.
These distortions around silicon are characteristic of
silyl ligands with electron withdrawing groups on
silicon. Bent’s rule13 states that as some substituents
on a central atom become more electronegative, increas-
ing amounts of s-character are diverted to the orbitals
used for bonding with the more electropositive substit-
uents. In this case, this is the transition metal fragment
OsCl(CO)(PPh3)2, and this may be an additional factor
serving to decrease the Os-Si bond length. The larger
p-character expected for the Si-F bonds results in a
(10) Allen, F. H.; Kennard, O. 3D Search and Research Using the
Cambridge Structural Database. Chemical Design Automation News
1993, 8, 1, 31.
(11) Woo, L. K.; Smith, D. A.; Young, V. G., J r. Organometallics
1991, 10, 3977.
(12) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, New York, 1960.
(13) Bent, H. A. Chem. Rev. 1961, 61, 275.

Os(SiR3)Cl(CO)(PPh3)2
Organometallics, Vol. 16, No. 23, 1997 5079
Ta ble 4. Resu lts of th e Geom etr y Op tim iza tion
a n d NBO An a lyses for th e Sila n es HSiR3 (R ) F ,
Cl, OH, Me)a
decrease of the F-Si-F angles from the ideal tetrahe-
dral angle of 109.5°.
One Si-F bond (Si-F2, bond length of 159.5(5) pm)
is significantly longer than the other two of 156.7(5) and
156.1(5) pm. The Si-F bond length in HSiF3 is 156.1(5)
pm.14 In Ni(SiF3)2(PMe3)3, where the only potential
π-acceptor ligands are SiF3, the average bond lengths
for the two sets of three Si-F bonds are longer at 159.6-
(9) and 158.0(8) pm.15 This is consistent with π-bond
formation between Ni and Si involving the Si-F σ*-
orbitals. The variation in the Si-F bond lengths
observed in Os(SiF3)Cl(CO)(PPh3)2 suggests that one
Si-F σ*-orbital may be more heavily involved in bond
formation to Os than the other two.
Because of the Cl/CO disorder problem in each of the
complexes 1b and 1d , it is not reasonable to expect
observable differentiation between the Si-R distances
for these compounds. The trihydroxysilyl derivative 1c,
which is not disordered, also has one silyl substituent
(O2) arranged nearly trans to the carbonyl ligand with
a torsion angle Cl-Os-Si-O2 of 14.4(2)°. However,
there are no significant differences between the three
Si-O distances found in 1c.
3a (R ) F) 3b (R ) Cl) 3c (R ) OH) 3d (R ) Me)
H-Si
Si-R
H-Si-R
R-Si-R
qH
145.7
160.2
110.7
108.3
-0.29
2.21
146.3
207.6
109.1
109.9
-0.19
1.23
145.5
164.2
106.5
112.3
-0.28
2.15
148.7
188.8
108.3
110.6
-0.24
1.55
qSi
qR
pop(3sSi
-0.64
0.68
-0.35
0.97
-0.62
0.64
-0.44
0.79
)
pop(3pSi
pop(3dSi
)
)
1.04
0.07
1.73
0.07
1.15
0.06
1.63
0.03
BO(H-Si)
BO(Si-R)
3 R f Si
0.70
0.34
16.4%
0.80
0.61
19.7%
0.69
0.26
16.4%
0.74
0.55
3.3%
a
Interatomic distances (pm) and angles (deg), charges q,
populations (pop), and atom-atom net linear bond orders (BO)
based on the NLMO/NPA.30
The Si-Cl bonds of Os(SiCl3)Cl(CO)(PPh3)2 were
found to be 205.9(8), 206.1(10) and 206.9(9)pm and these
are significantly longer than the average of 202 pm
found for Si-Cl bond lengths in chlorosilane mol-
ecules.16 Similarly, long Si-Cl distances of 206.7, 206.9,
and 207.2 pm were found in CpFe(SiCl3)(CO)2,17 for
which some multiple bond between silicon and iron was
proposed through photoelectron spectroscopy.2 It is,
therefore, possible that some degree of multiple bonding
may be present in the Os-Si bond of 1b. In contrast,
the Si-C bond lengths of the SiMe3 group in Os(SiMe3)-
Cl(CO)(PPh3)2 (average 188.5 pm) appear normal.
The average angles R-Si-R and Os-Si-R on going
from 1a -d are found to be 101.5°, 101.1°, 105.0°, 104.6°
and 116.5°, 116.9°, 113.6°, 114.0°, respectively. Al-
though the general trends are in the direction expected
from application of Bent’s rule, the changes are very
small and not uniform throughout this series of com-
pounds. It is also difficult to predict the relative
influence that steric factors have on these parameters.
Ab In itio Ca lcu la tion s. Model complexes Os(SiR3)-
Cl(CO)(PH3)2 (2a -d ; R ) F, Cl, OH, Me) were con-
structed following the usual practice of replacing the
bulky triphenylphosphine groups by PH3, recognizing
that the Os-P bond lengths will be underestimated.
Geometry optimizations were performed on each of the
four model compounds as well as on the parent silanes
HSiR3 (3a -d ; R ) F, Cl, OH, Me). A comparison with
the experimentally obtained data for the transition
metal complexes is shown in Table 3. The results of
the calculations on the free silanes 3a -d are listed in
Table 4. The agreement between calculated and ob-
served structures is generally good regarding the level
of approximation used and the fact that solid-state
effects are neglected. The results are certainly suf-
ficiently good for the discussion of bond properties and
F igu r e 2. BLYP optimized structure of Os(SiF3)Cl(CO)-
(PH3)2 (2a ).
trends. In the following discussion, the term in plane
(as opposed to out of plane) is used for atoms or orbitals
which are part of the mirror plane (Cs symmetry) of the
molecule. Technical details relating to the calculations
can be found under Computational Details in the
Experimental Section.
A simple comparison between Figures 1 and 2 shows
that the calculated complexes 2a -d have the same
conformation as the structures 1a -d obtained by X-ray
crystallography. With no influence from packing effects,
the structures of the computed species 2a -d show
perfect Cs symmetry with one substituent on silicon
located exactly trans to the carbonyl group on osmium.
In the following discussion, most of the trends in bond
angles and distances occur when the substituents on
silicon change in the order fluorine to chlorine to
hydroxy to methyl. However, the group electronega-
tivities of the different SiR3 ligands with or without
taking into account the calculated charges for those
fragments shows the following descending values: SiF3
(3.35 or 3.47) > Si(OH)3 (3.01 or 3.10) > SiCl3 (2.78 or
2.76) > SiMe3 (2.27 or 2.30).9 This correlates with the
order of the electronegativities of the substituents on
silicon itself with F (3.89) > OH (3.22) > Cl (2.95) >
Me (2.27).9 However, chlorine is similar in size to silicon
and, therefore, forms covalent bonds more readily with
this element than the other three substituents. Thus,
only comparison of the different electronegativities of
the second period elements are unambiguous.
(14) Eaborn, C. Organosilicon Compounds; Butterworths Scientific
Publications: London, 1960.
(15) Bierschenk, T. R.; Guerra, M. A.; J uhlke, T. J .; Larson, S. B.;
Lagow, R. J . J . Am. Chem. Soc. 1987, 109, 4855.
(16) J olly, W. L. The Principles of Inorganic Chemistry; McGraw-
Hill: New York, 1976; p 33.
(17) Schubert, U.; Kraft, G.; Walther, E. Z. Anorg. Allg. Chem. 1984,
519, 96.

5080 Organometallics, Vol. 16, No. 23, 1997
Hu¨bler et al.
Ta ble 5. Resu lts of th e NBO An a lyses for th e
Mod el Com p lexes Os(SiR3)Cl(CO)(P H3)2 (2a -d )a ,b
compound
2a (R ) F) 2b (R ) Cl) 2c (R ) OH) 2d (R ) Me)
qOs
-0.43
2.08
-0.65
-0.66
0.11
-0.35
1.08
-0.40
2.09
-0.62
-0.64
0.19
-0.38
1.59
-0.44
-0.47
0.21
qSi
qRi
c
-0.35
-0.38
-0.03
-0.46
0.43
c
qRo
qSiR3
qCl
qC
-0.47
0.41
-0.49
0.38
-0.51
0.42
qO
qP
-0.46
0.26
-0.46
0.27
-0.51
0.27
-0.50
0.28
ENR
3.89
2.95
3.22
2.27
F igu r e 3. (a) Contour plot of the natural localized molec-
ular orbital (NLMO) for the delocalization of the lone pair
lpi on osmium for Os(SiF3)Cl(CO)(PH3)2 (2a ) generated with
the program MOLDEN.33 (b) Contribution of silicon orbitals
to this NLMO. Full lines designate positive and dotted lines
designate negative values of the orbital changing in steps
of 0.02 for part a and 0.002 for part b.
ENSiR3
ENSiR3(qSiR3
3.35
3.47
0.73
1.11
2.78
2.76
1.04
1.81
3.01
3.10
0.67
1.17
2.27
2.30
0.82
1.54
)
pop(3sSi
)
pop(3pSi
pop(3dSi
)
)
0.07
0.06
0.06
0.03
BO(Os-Si)
BO(Os-Cl)
BO(Os-C)
BO(Os-P)
BO(Si-Ri)c
BO(Si-Ro)c
BO(C-O)
0.79
0.35
1.19
0.52
0.32
0.31
1.44
0.09
0.16
0.94
0.32
1.20
0.53
0.57
0.56
1.44
0.10
0.14
0.73
0.25
1.40
0.50
0.35
0.34
1.43
0.05
0.11
0.71
0.23
1.40
0.51
0.53
0.52
1.43
0.05
0.10
0.05
1.1%
0.5%
7.1%
4.2%
BO(Si-Cl)
BO(Si-CO)
BO(Si-P)
0.05
0.05
0.05
lpi(Os) f Sic
lpo(Os) f Sic
lpi(Os) f C(O)c
3 R f Si
4.8%
1.9%
14.6%
16.2%
2.4%
2.5%
13.7%
19.0%
1.6%
1.1%
10.7%
15.9%
a
Charges q and populations (pop).30 Electronegativities (EN)
on the Pauling scale are calculated according to literature.9
Atom-atom net linear bond orders (BO) and delocalization of
b
F igu r e 4. Contour plots for the delocalization of the lone
pair lpo on osmium for Os(SiF3)Cl(CO)(PH3)2 (2a ) analogous
to those shown in Figure 3.
the lone pairs on osmium as well as of the lone pairs (lp) and bonds
of the R groups based on the NLMO/NPA analyses.30 c The index
i stands for in plane (Cs) and the index o for out of plane.
bonding or rehybridization.18 Ionic contributions would,
hence, explain the Os-Si bond shortening of 11.5 pm
when comparing 2a (231.2 pm) with 2d (242.7 pm). On
the other hand, it is surprising that the calculated Os-
Si bond length in Os(SiCl3)Cl(CO)(PPh3)2 is almost as
short as that in Os(SiF3)Cl(CO)(PPh3)2 and much shorter
than that in Os[Si(OH)3]Cl(CO)(PPh3)2, although the
group electronegativity of SiCl3 (2.76) is much smaller
than those of SiF3 (3.47) and Si(OH)3 (3.10). This clearly
shows that factors other than ionic contributions alone
have to be considered to explain the differences in the
Os-Si distances in the set of five-coordinate silyl
complexes 2a -d .
As the Os-Si distances become shorter on changing
the nature of R, a corresponding lengthening of the
Si-R bonds also occurs. The average Si-R values for
the calculated complexes are found to be 2.8 (2a ), 5.0
(2b), 2.1 (2c), and 1.3 pm (2d ) longer than those
obtained from optimizations on the corresponding free
silanes 3a -d . When considering only the second row
derivatives 2a , 2c, and 2d , the largest effect is observed
for the trifluorosilyl compound, the complex with the
highest group electronegativity for the silyl substituent,
and gets smaller with decreasing electronegativities.
However, the lengthening of 5.0 pm for the Si-Cl bond
in 2b is much larger than those observed for the second
period analogues. This is due to both the larger value
of the Si-Cl bond length compared to the other Si-R
(R ) F, OH, Me) bonds and the fact that the Si-Cl bond
in HSiCl3 (3b) is in turn relatively short. This arises
because of a higher back-bonding from chlorine to silicon
Figures 3a and 4a show in-plane and out-of-plane
electron isodensity contour maps for the delocalization
of the lone pairs on osmium of complex 1a . Figures 3b
and 4b depict the contributions of silicon orbitals to the
NLMOs in the corresponding parts a. Table 5 sum-
marizes the results for the NBO analyses of 1a -d .
Comparable parameters of the NBO analyses for the
free silanes 3a -d are listed in Table 4.
Most of the calculated bond distances in the model
compounds 2a -d are longer than the parameters
obtained from the X-ray data (see Experimental Section,
Computational Methods), but they show the same
trends that were found in the solid-state structures 1a -
d . The Os-Si distances, for example, are consistently
overestimated by 5-6 pm in the BLYP calculations and
change from 231.2 (2a ) to 232.0 (2b), 237.0 (2c), and
242.7 pm (2d ). These changes in bond lengths correlate
partly with the difference between the electronegativity
of the osmium fragment and the silyl group, ∆EN(OsSi),
and this raises the question of the importance of ionic
contributions in determining the length of the Os-Si
bond. Since the charge on osmium in the complexes
2a -d is almost invariant, the electronegativity of the
osmium fragment can be considered to be approximately
the same in all complexes and most likely to be smaller
than 2.3, the value calculated for the trimethylsilyl
compound 2d . Since the group electronegativity of SiF3
is larger by 1.17 than the value for SiMe3, ∆EN(OsSi)
also increases by 1.17 when going from the trimethyl-
silyl (2d ) to the triflourosilyl derivative (2a ). According
to Schomaker and Stevenson, an increase of 1.17 units
in ∆EN is related to a shortening of approximately 10.5
pm in the corresponding bond in the absence of multiple
(18) Douglas, B.; McDaniel, D. H.; Alexander, J . J . Concepts and
Models of Inorganic Chemistry, 2nd ed.; Wiley: New York, 1983; p 78.

Os(SiR3)Cl(CO)(PPh3)2
Organometallics, Vol. 16, No. 23, 1997 5081
(19.6%) when compared with the much smaller values
for the delocalization of the lone pairs of fluorine (16.4%)
and hydroxy (16.4%) in HSiF3 (3a ) and HSi(OH)3 (3c),
respectively. This effect partly reverses the electron-
withdrawing effect of the electronegative chlorine atoms
and, therefore, also explains the lowest charge on silicon
of only +1.23 and +1.08 in both the free silane HSiCl3
(3b) and the trichlorosilyl complex Os(SiCl3)Cl(CO)-
(PPh3)2 (2b), respectively.
polarization of a silicon a p-orbital with 10.8% d-orbital
contribution toward the osmium center. The d-orbital
contribution to the orbital shown in Figure 3b is only
3.7%.
A second important result of the NLMO analysis is
the high bond order between silicon and the carbon of
the carbonyl group. This parameter increases from 0.10
to 0.11, 0.14, and 0.16 when going from 2d to 2c, 2b,
and 2a and correlates directly with the observed stretch-
ing frequencies of the carbonyl groups. This interaction
is consistent with the very small Si-Os-C(O) angle
found for 2a -d . The ν(CO) values for these compounds
could, therefore, be influenced by a direct interaction
between the silyl groups and the CO ligands as well as
the electron-withdrawing or π-accepting nature of the
silyl group reducing the electron density at the osmium
center. There is precedent for Si-CO interactions in
the compound Cp2Zr(η2-Me2SidNtBu)(CO).19
The harmonic vibrational analyses were not in good
agreement with the experimentally obtained data,
which is a common feature when modeling large mol-
ecules at a relatively moderate level of theory. Never-
theless, the calculated higher frequencies of 1834 and
1836 cm-1 for the trifluoro and trichloro complexes
respectively, and lower values of 1793 and 1800 cm-1
for the trihydroxy and trimethyl derivatives show some
acceptable agreement with the experimentally obtained
values.
Another frequently discussed feature in this context
are the bond angles on silicon. According to Bent’s rule,
smaller angles are found between substituents with
higher electronegativity, and this results in a larger
s-character for the orbital pointing toward an electro-
positive atom and, therefore, a shorter bond distance
to this atom.13 Since the group electronegativities of
Si(OH)3 (3.10) and SiMe3 differ by as much as 0.80 units,
and the average Os-Si-R angles are almost invariant
with values of 112.0° and 111.8°, respectively, this
criterion is not applicable at least for the complexes
2a -d discussed here.
As a further explanation, the particularly short Os-
Si distances in 2a and 2b can also be attributed to
multiple bonding between these two centers. Multiple
bonding can most easily arise through interaction of the
osmium d-orbitals with either the silicon d-orbitals or
a suitable combination of σ*-orbitals of the SiR3 group.
The two lone pairs on osmium, in plane (lpi(Os)) and
out of plane (lpo(Os)) with respect to the Cs-symmetry
of the molecule, delocalize into hybrids on silicon by
4.8% (2a , Figure 3), 2.4% (2b), 1.6% (2c), and 1.1% (2d )
as well as 1.9% (2a , Figure 4), 2.5% (2b), 1.1% (2c), and
0.5% (2d ), respectively, while the donation into the
carbonyl π*-orbitals of 14.6% (2a , Figure 3a), 13.7% (2b),
10.7% (2c), and 7.1% (2d ) is considerably larger. This
leads to a strengthening and shortening of the Os-Si
bond due to multiple bonding. The effect increases in
the order Me < OH < Cl < F, and the Os-Si distances
decrease in the same order. As discussed earlier, the
Os-Si bond lengths are overestimated by 5-6 pm, and
calculations with the geometry fixed at that observed
by X-ray crystallography for 1a showed increased de-
localization from osmium to silicon (e.g., 7.2% for lpi(Os)
in 2a ) and decreased delocalization from osmium to the
carbonyl group (e.g., 11.6% for lpi(Os) in 2a ). Therefore,
the SiF3 group can be estimated to have almost half the
π-acceptor ability of a carbonyl group. This is in good
agreement with the results deduced from the photoelec-
tron spectra on CpFe(SiCl3)(CO)2 for which the SiCl3
group is estimated to have about half of the π-acceptor
ability of a carbonyl group in this compound.
Con clu sion s
The acquisition of X-ray structural data for a set of
five-coordinate osmium-silyl complexes with the silyl
ligand changing from SiF3 to SiCl3 to Si(OH)3 to SiMe3
provided the opportunity to study the influence of a wide
range of different SiR3 groups on the nature of the
osmium-silicon bond. Besides a likely strengthening
of the Os-Si σ-bond due to ionic contributions only, ab
initio calculations and subsequent NBO analyses re-
vealed an increasing importance of π-bonding when
going from the methyl to the hydroxy, the chloro, and
finally the fluoro derivative. The group with the highest
electronegativity, SiF3, was estimated to have almost
half the π-acceptor ability of the carbonyl group in the
same molecule. No higher d-orbital population on
silicon was found in any complex when compared with
the corresponding free silanes, and the osmium d-
orbitals mostly donate into a linear combination of Si-R
σ*-orbitals to form the π-bond. Nonetheless, d-orbitals
on silicon are important in the quantitative description
of the Os-Si bond as they serve to polarize the Si-R
σ*-orbitals, and this not only enhances the π-bonding
between osmium and silicon but also diminishes the
antibonding between Si and F, Cl, OH, and Me. The
CO stretching frequencies were found to increase in the
order Me to OH, Cl, and F. This is commonly explained
with a diminished electron density at the osmium center
if more electronegative groups are introduced into the
complex. Population analyses on the set of five-
coordinate osmium-silyl complexes show that this effect
is also due to a direct influence of the silyl ligand on
the carbonyl group in terms of a three-center bond
A comparison between the free silanes 3a -d and the
corresponding silyl complexes 2a -d shows no signifi-
cant changes of the d-orbital populations on silicon.
Nonetheless, the d-orbitals serve to polarize the Si-R
σ*-orbitals in the transition metal complexes 2a -d in
such a way that this enhances the π-bonding between
Si and Os and diminishes antibonding between Si and
R (R ) F, Cl, OH, and Me). Indeed, calculations without
silicon d-orbitals show that they are important for a
quantitative description of the bonding situation. Fig-
ure 3a shows no nodal plane between silicon and the in
plane fluorine atom, whereas the nodal plane of the Si-
Fi σ*-orbitals is still present when neglecting the
d-orbitals on silicon. Figure 4b depicts the important
(19) Procopio, L. J .; Carroll, P. J .; Berry, D. H. Polyhedron 1995,
14, 45.

5082 Organometallics, Vol. 16, No. 23, 1997
Hu¨bler et al.
symmetry restrictions starting from different geometries
including the coordinates obtained from the X-ray analyses.
To study the bonding situation in more detail, the natural
localized molecular orbitals (NLMOs)30 based on natural bond
orbital (NBO)31 analyses were computed for all geometry-
optimized structures by the following procedure. First, two-
center, two-electron bonds were calculated for all model
complexes with two double bonds from the carbon atom of the
carbonyl group to both osmium and oxygen. The set of NBOs
automatically found by the NBO program for the free silanes
include one H-Si bond and three single bonds between silicon
and the three R groups. In the second step, the systems were
allowed to delocalize.
between osmium, silicon, and the carbon of the CO
group which decreases in the order F > Cl > OH > Me.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were carried out using
standard Schlenk techniques in a dry atmosphere of oxygen-
free dinitrogen. The solvents were carefully dried and distilled
from the appropriate drying agents prior to use.20 NMR
spectra were measured at 25 °C on either a Bruker AM 400
or a DRX 400 spectrometer at 400.128 (1H), 100.625 (13C),
376.478 (19F), 79.495 (29Si), and 161.976 MHz (31P). All
chemical shifts were recorded in ppm downfield from tetra-
methylsilane (1H, 13C, 29Si), fluorotrichloromethane (19F), or
Os(SiF 3)Cl(CO)(P P h 3)2 (1a ). Os[Si(OH)3]Cl(CO)(PPh3)2
(0.100 g, 0.117 mmol) was dissolved in dichloromethane (5 mL)
and ethanol (5 mL). Aqueous HF (40%) (2 mL) was added,
and the solution was stirred vigorously for 20 min. After
ethanol (20 mL) was added, the yellow product was collected
by filtration and washed well with ethanol-water-ethanol.
Recrystallisation from CH2Cl2/ethanol gave pure 1a (0.094 g,
93%). Mp 221-226 °C; 1H NMR (CDCl3) δ 7.60-7.36 (m, 30H,
phosphoric acid (31P) on the δ scale. The carbon phosphorus
n/m
coupling
J
in the triphenylphosphine ligand stands for
CP
n
| J CP
+
mJ CP|. Infrared spectra were recorded on a Digilab
FTS-7 infrared spectrometer. Melting points are reported in
degrees Celsius (uncorrected). Analytical data were obtained
from the Microanalytical Laboratory, University of Otago. The
compounds OsPhCl(CO)(PPh3)2,4 OsHCl(CO)(PPh3)3,21 and Os-
2
P(C6H5)3); 13C NMR (CDCl3) δ 179.2 (t, J CP ) 8.6 Hz, CO),
6
[Si(OH)3]Cl(CO)(PPh3)2 were all prepared according to litera-
2/4
1/3
134.4 (t′,
J
) 5.5 Hz; o-C6H5), 130.7 (t′,
J
) 26.2 Hz,
CP
CP
ture procedures.
3/5
i-C6H5), 130.7 (s, p-C6H5), 128.5 (t′,
J
) 5.0 Hz, m-C6H5);
CP
2
Com p u ta tion a l Meth od s. All calculations were per-
formed with the GAUSSIAN9422,31 program series. The den-
sity functional method applying Beckes 1988 gradient-
corrected exchange functional23 and the correlation functional
of Lee, Yang, and Parr (BLYP) was applied.24 Structures were
fully optimized at all levels of theory using gradient tech-
niques. Stationary points were confirmed by frequency analy-
sis. Effective core potentials were used to represent the 60
innermost electrons of the osmium atom,25 as well as the 10-
electron core of the silicon and phosphorus atoms.26 The
valence double-ú basis sets with a (341/321/21) contraction for
osmium and a (21/21) contraction for silicon, phosphorus, and
chlorine were those associated with the pseudopotentials
(LANL2DZ basis set22), supplemented with a polarization of
the d-shell for silicon.27 Carbon, oxygen, and fluorine atoms
were described by Dunning/Huzinaga double-ú basis sets using
a (721/41) contraction.28 For the hydrogen atoms, a set of (31)
contracted basis functions29 were used. These basis set
limitations were necessary due to the large computer time and
disk space requirements for the DFT calculations. Although
the resulting optimized complexes showed almost perfect Cs
symmetry, the optimizations were carried out without any
29Si NMR (CH2Cl2/CDCl3) δ -74.3 (qt, J SiP ) 16.3, J SiF
)
1
333.7 Hz); 19F NMR (CDCl3) δ -89.64 (s); IR (Nujol) ν 1954
(CO), 1931 (CO), 880 (SiF), 866 (SiF), 820 (SiF); solution IR
(CH2Cl2) 1946 (CO). Anal. Calcd for C37H30ClF3OP2SiOs
(863.32): C, 51.48; H, 3.50. Found: C, 51.10; H, 3.98.
Os(SiCl3)Cl(CO)(P P h 3)2 (1b). (a) HSiCl3 (0.470 g; 3.5
mmol) was introduced to a solution of OsPhCl(CO)(PPh3)2
(0.200 g; 0.23 mmol) in dry toluene (10 mL) in a Schlenk tube,
which was then sealed. The solution was heated at 40 °C with
stirring for 30 min. The yellow solution was evaporated to a
small volume in vacuo, and then dry n-hexane was added to
effect crystallization of 1b (0.188 g, 88%). (b) HSiCl3 (0.530
g, 4.0 mmol) was added to a solution of OsHCl(CO)(PPh3)3
(0.200 g; 0.19 mmol) in dry toluene (10 mL) in a Schlenk tube,
which was then sealed. The solution was heated to 60 °C with
stirring for 20 min. Pure, yellow crystals of 1b were afforded
by reduction of the volume of the solution in vacuo, and then
1
dry n-hexane was added (0.165 g, 94%). Mp 200-203 °C; H
NMR (CDCl3) δ 7.75-7.30 (m, 30H; P(C6H5)3); 13C NMR
(CDCl3, with Cr(acac)3 as a relaxation reagent): δ 179.6 (t,
2J CP ) 8.5 Hz, CO), 134.7 (t′, 2/4J CP ) 5.1 Hz, o-C6H5), 130.7 (s,
1/3
3/5
p-C6H5), 130.0 (t′,
J
) 26.2 Hz, i-C6H5), 128.3 (t′,
J
)
CP
CP
4.7 Hz; m-C6H5); 31P NMR (CH2Cl2/CDCl3) 22.7 (s); IR (Nujol)
ν 1944 (CO). Anal. Calcd for C37H30Cl4OSiP2Os (912.69): C,
48.69; H, 3.31. Found: C, 48.71; H, 3.26.
(20) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: New York, 1988.
(21) Vaska, L. J . Am. Chem. Soc. 1964, 86, 1943.
(22) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith, T.; Petersson,
G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Cioslowski, J .;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala,
P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts,
R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, J .;
Stewart, J . P.; Head-Gordon, M.; Gonzalez, C.; Pople, J . A. Gaussian
94, Revision D.3, Gaussian, Inc.: Pittsburgh, PA, 1995.
(23) Becke, A. D. Phys. Rev. 1988, A38, 3098.
(24) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. 1988, B37, 785.
Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989,157,
200.
(25) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985, 82, 299.
(26) Wadt, W. R.; Hay, P. J . J . Chem. Phys. 1985, 82, 284.
(27) Francl, M. M.; Pietro, W. J .; Hehre, W. J .; Binkley, J . S.; Gordon,
M. S.; DeFrees, D. J .; Pople, J . A. J . Chem. Phys. 1982, 77, 3654.
(28) Dunning, T. H., J r.; Hay, P. J . In Modern Theoretical Chemistry;
Schaefer, H. F., Ed.; Plenum: New York 1976; pp 1ff.
Os(SiMe3)Cl(CO)(P P h 3)2 (1d ). MeLi (0.009 g, 0.43 mmol)
in diethyl ether was added to Os(SiCl3)Cl(CO)(PPh3)2 (0.120
g, 0.13 mmol) in dry toluene (5 mL) with stirring at room
temperature. Immediately, the color of the solution changed
from yellow to red-orange. The solution was stirred for several
minutes before the volume of the solvent was reduced by half
in vacuo. The solution was then placed on a flash column with
a silica gel support and chromatographed using an eluent of
toluene/n-hexane (80:20). The yellow-orange band eluted first
from the column was collected, and the solvent was removed
under reduced pressure. Recrystallization of the residual solid
using CH2Cl2/n-hexane yielded yellow-orange crystals of pure
1d (0.040 g, 36%). Mp 181-182 °C; 1H NMR (CDCl3) δ 7.60-
7.34 (m, 30H, P(C6H5)3), 0.14 (s, 9H, Si(CH3)3); 13C NMR
2
2/4
(CDCl3) δ 183.2 (t, J CP ) 8.1 Hz, CO), 134.6 (t′,
J
) 4.9
CP
1/3
(29) Ditchfield, R.; Hehre, W. J .; Pople, J . A. J . Chem. Phys. 1971,
54, 724. Hehre, W. J .; Ditchfield, R.; Pople, J . A. Ibid 1972, 56, 2257.
Hariharan, P. C.; Pople, J . A. Mol. Phys. 1974, 27, 209. Gordon, M. S.
Chem. Phys. Lett. 1980, 76, 163. Hariharan, P. C.; Pople, J . A. Theor.
Chim. Acta 1973, 28, 213.
Hz, o-C6H5), 132.4 (t′,
J
) 24.5 Hz, i-C6H5), 130.0 (s,
CP
3/5
p-C6H5), 128.0 (t′,
J
) 4.5 Hz, m-C6H5), 9.1 (s, Si(CH3)3);
CP
31P NMR (CH2Cl2/CDCl3) δ 21.9 (s); IR (Nujol) ν 1910 (CO),
1888 (CO), 835 (SiC); solution IR (CH2Cl2) ν 1895 (CO). Anal.
(30) Reed, A. E.; Weinhold, F. J . Chem. Phys. 1985, 83, 1736. Reed,
A. E.; Schleyer, P. v. R. J . Am. Chem. Soc. 1990, 112, 1434.
(31) Glendening, E. D.; Reed, A. E.; Carpenter, J . E.; Weinhold, F.
NBO, Version 3.1; part of Gaussian 94, Revision D.3; Gaussian, Inc.,
Pittsburgh, PA, 1995.
Calcd for
Found: C, 56.92; H, 5.11.
X-r a y Exp er im en ta l Da ta for 1a , 1b‚CH2Cl2, a n d 1d .
Data were collected on an Enraf-Nonius CAD4 diffractometer.
C40H39ClOP2SiOs (851.43): C, 56.43; H, 4.62.

Os(SiR3)Cl(CO)(PPh3)2
Organometallics, Vol. 16, No. 23, 1997 5083
An empirical absorption correction was applied. The structure
was solved by Patterson methods, and refinement on F2 was
carried out by full-matrix least-squares techniques
(SHELXL93).32 Anisotropic temperature factors were used for
all non-hydrogen atoms except for the water molecule. Hy-
drogen atoms were included in calculated positions with
isotropic temperature factors 20% higher than the correspond-
ing carbon atoms. Further results of the refinement are listed
in Table 2.
Ack n ow led gm en t. We thank the Alexander von
Humboldt-Stiftung for the award of a Feodor-Lynen
scholarship to K.H. X-ray data for compound 1d was
generously provided by G. R. Clark. Support from the
AURC (Auckland) is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, thermal parameters, and interatomic distances
and angles for 1a and 1d (19 pages). Ordering information is
given on any current masthead page.
(32) Sheldrick, G. M. SHELXL93; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1993.
(33) Schaftenaar, G. MOLDEN 3.2, CAOS/CAMM Center: The
Netherlands, 1996.
OM970580H