CO-induced C(sp2)/C(sp) coupling on Ru and Os: A comparative study

Article abstract of DOI:10.1021/om970961v

Reaction of OsHCl(=C=CHSiMe₃)(PⁱPr₃)₂ with HC≡CSiMe₃ gives OsCl{(E)-CH=CHSiMe₃}-(C=CHSiMe₃)(PⁱPr ₃)₂, which reacts with excess CO to give the C-C coupling product OsCl-{C(CH=CHSiMe₃)=CHSiMe₃}(CO)₂(P ⁱPr₃)₂. Reaction of[RuH(CO)(P^tBu₂Me)₂]⁺ (as its B(3,5-(CF₃)₂C₆H₃)₄ ^- salt) with 2 mol of HC≡CSiMe₃ gives immediately the C-C coupling product [Ru{η³-(Me₃Si)CH=C-CH=CH(SiMe₃)}(CO)(P ^tBu₂Me)₂]⁺. The crystal structure of this latter product reveals one agostic ^tBu C-H interaction with Ru. Ab initio (DFT B3LYP) calculations show the presence of two isomeric structures as minima on the potential energy surface, one with vinyl and vinylidene ligands, and the other with a butadienyl ligand bonded in an η³ manner to the metal. The calculations show a strong preference for the butadienyl structure when the metal fragment is Ru(CO)L₂⁺ and a nearly degenerate situation when the metal fragment is OsClL₂ (L = PH₃).

Full text of DOI:10.1021/om970961v

4700
Organometallics 1998, 17, 4700-4706
CO-In d u ced C(sp 2)/C(sp ) Cou p lin g on Ru a n d Os: A
Com p a r a tive Stu d y
Dejian Huang, Montserrat Oliva´n, J ohn C. Huffman, Odile Eisenstein,*,† and
Kenneth G. Caulton*,‡
Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington,
Indiana 47405-4001, and LSDSMS (UMR 5636) Case Courrier 14, Universite´ de Montpellier
2, 34095 Montpellier Cedex 5, France
Received November 4, 1997
Reaction of OsHCl(dCdCHSiMe3)(PiPr3)2 with HCtCSiMe3 gives OsCl{(E)-CHdCHSiMe3}-
(CdCHSiMe3)(PiPr3)2, which reacts with excess CO to give the C-C coupling product OsCl-
{C(CHdCHSiMe3)dCHSiMe3}(CO)2(PiPr3)2. Reaction of [RuH(CO)(PtBu2Me)2]+ (as its B(3,5-
(CF3)2C6H3)4- salt) with 2 mol of HCtCSiMe3 gives immediately the C-C coupling product
[Ru{η3-(Me3Si)CHdC-CHdCH(SiMe3)}(CO)(PtBu2Me)2]+. The crystal structure of this latter
product reveals one agostic tBu C-H interaction with Ru. Ab initio (DFT B3LYP) calculations
show the presence of two isomeric structures as minima on the potential energy surface,
one with vinyl and vinylidene ligands, and the other with a butadienyl ligand bonded in an
η3 manner to the metal. The calculations show a strong preference for the butadienyl
+
structure when the metal fragment is Ru(CO)L2 and a nearly degenerate situation when
the metal fragment is OsClL2 (L ) PH3).
In tr od u ction
those introduced in the preceding paragraph. In es-
sence, this work represents a comparison of the differ-
ences between isoelectronic species based on OsCl vs
Ru(CO)+.
This is a study of two initially distinct research
themes which converge and which, taken together,
reveal more than either individual result.
The molecules MH3ClL2 (M ) Ru, Os and L ) PiPr3
or PtBu2Me) are dehydrogenated by terminal alkynes
according to eq 1. One molecule of alkyne is rearranged
Exp er im en ta l Section
Gen er a l. All reactions and manipulations were conducted
using standard Schlenk and glovebox techniques under prepu-
rified argon. Solvents were dried and distilled under nitrogen
or argon and stored in airtight solvent bulbs with Teflon
closures. All NMR solvents were dried, vacuum-transferred,
and stored in a glovebox. 1H, 19F, 13C{1H}, and 31P{1H} NMR
spectra were obtained on a Varian Gemini 300 spectrometer.
Chemical shifts are referenced to residual solvents peaks (1H,
13C{1H}) or external H3PO4 (31P{1H}) and CFCl3 (19F). OsH3-
Cl(PiPr3)2,4 OsHCl(dCdCHSiMe3)(PiPr3)2,1 RuH(OTf)(CO)(Pt-
5
Bu2Me)2,3 and NaBAr′4 were synthesized according to pub-
(hydrogen migration), and the result is a 16-electron
(carbonyl-free) vinylidene complex.1 The remaining
M-H moiety is a potential site for addition of added
alkyne; this reaction will be described here.
lished procedures. HCtCSiMe3 (Oakwood) was distilled and
degassed prior to use. Infrared spectra were recorded on a
Nicolet 510P FT-IR spectrometer. Elemental analyses were
performed on a Perkin-Elmer 2400 CHNS/O analyzer at the
Chemistry Department, Indiana University.
The molecular ions [RuR(CO)L′2]+ (R ) H or Ph and
OsCl{(E)-CH dCH SiMe3}(dCdCH SiMe3)(P iP r 3)2,
3.
-
L′ ) PtBu2Me) with BAr′4 counterion (Ar′ ) 3,5-
Meth od A. To a solution of OsH3Cl(PiPr3)2 (1) (100 mg, 0.18
mmol) in toluene (7 mL) was added HCtCSiMe3 (77 µL, 0.55
mmol). The resulting red solution was stirred for 12 h at room
temperature. Then, the solution was filtered through Celite,
and the volatiles were removed under vacuum, yielding a red
solid. Yield: 95 mg (74%). Alternatively (Meth od B), this
compound can be prepared by adding HCtCSiMe3 (22 µL,
0.155 mmol) to a solution of OsHCl(dCdCHSiMe3)(PiPr3)2 (2)
(100 mg, 0.155 mmol) in toluene (5 mL) and stirring at room
temperature for 12 h. Yield: 81 mg (70%). Anal. Calcd for
(CF3)2C6H3) are apparent 14-electron species, which are
lightly “stabilized” by two agostic tBu C-H groups, one
from each L′.2,3 As such, they are expected to bind
Lewis bases, and we report here the reaction of [RuH-
(CO)L′2]+ with terminal alkynes. It will become appar-
ent that the species [RuR(CO)L′2]+ are a source of
carbonyl-containing species which are analogous to
† E-mail: eisenst@lsd.univ-montp2.fr.
‡ E-mail: caulton@indiana.edu.
C
28H63ClOsP2Si2: C, 45.23; H, 8.54. Found: C, 45.54; H, 7.98.
(1) Oliva´n, M.; Eisenstein, O.; Caulton, K. G. Organometallics 1997,
16, 2227.
(2) Huang, D.; Streib, W. E.; Eisenstein, O.; Caulton, K. G. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2004.
(3) Huang, D.; Huffman, J . C.; Bollinger, J . C.; Eisenstein, O.;
Caulton, K. G. J . Am. Chem. Soc. 1997, 119, 7398.
(4) Kuhlman, R. L.; Gusev, D. G.; Eisenstein, O.; Caulton, K. G.
Submitted.
(5) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920.
S0276-7333(97)00961-8 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 09/19/1998

CO-Induced C(sp2)/ C(sp) Coupling on Ru and Os
Organometallics, Vol. 17, No. 21, 1998 4701
Ta ble 1. Cr ysta llogr a p h ic Da ta d
1H NMR (300 MHz, C6D6, 20 °C): δ -0.11 (dt, J P-H ) 2.7 Hz,
J H-H ) 3.9 Hz, 1H, OsdCdCH), 0.09, 0.23 (both s, each 9H,
SiMe3), 1.28 (dvt, J H-H ) 7.2 Hz, N ) 12.6 Hz, 18H, PCH-
(CH3)2), 1.29 (dvt, J H-H ) 7.2 Hz, N ) 13.2 Hz, 18H, PCH-
(CH3)2), 3.08 (m, 6H, PCH(CH3)2), 4.79 (dt, J P-H ) 2.1 Hz, J H-H
) 13.5 Hz, 1H, Os-CHdCHSiMe3), 8.53 (dd, J H-H ) 3.9 Hz,
J H-H ) 13.5 Hz, 1H, Os-CHdCHSiMe3). 13C{1H} NMR (75
MHz, C6D6, 20 °C): δ -0.28 (s, SiMe3), 2.16 (s, SiMe3), 19.84,
20.14 (both s, PCH(CH3)2), 23.99 (t, N ) 11.8 Hz, PCH(CH3)2),
87.19 (t, J P-C ) 2.5 Hz, OsdCdC), 130.87 (t, J P-C ) 2.8 Hz,
formula
color
[C61H75BF24OP2RuSi2] C28H63ClOsP2Si2
orange
red
cryst dimens (mm)
0.34 × 0.34 × 0.42
0.21 × 0.20 ×
0.25
space group
cell dimens
a (Å)
b (Å)
c (Å)
Pna21
P21
(at -170 °C)
24.056(2)
18.440(2)
15.789(1)
(at -170 °C)
7.961(1)
10.710(1)
20.697(3)
90.10(1)
2
â (deg)
Z
4
Câ vinyl), 153.99 (t, J P-C ) 7.2 Hz, CR vinyl), 272.33 (t, J P-C
)
volume
7003.85
1.421
0.710 69
1510.22
4.1
1764.68
1.399
0.710 69
743.58
38.61
6
45
2541
2453
828
2377
2178
0.019
9.6 Hz, OsdCdC). 31P{1H} NMR (121 MHz, C6D6, 20 °C): δ
14.1 (s). IR (Nujol, cm-1): ν(CdC) 1593 (m), 1528 (m).
calcd density
wavelengtha
mol wt
OsCl{C(CH dCHSiMe3)dCHSiMe3}(CO)2(P iP r 3)2, 4.
A
solution of OsCl(CHdCHSiMe3)(dCdCHSiMe3)(PiPr3)2 (100
mg, 0.13 mmol) in toluene (7 mL) was frozen in liquid N2, the
headspace of the Schlenk flask was evacuated, and excess CO
(1 atm) was introduced. On warming to room temperature
and stirring, the solution color changed from deep red to dark
yellow. After stirring for 45 min, the volatiles were removed
under vacuum, and pentane was added to give a yellow
solution that was cooled at -40 °C, yielding white microcrys-
tals. Yield: 43 mg (40%). Anal. Calcd for C30H63ClO2OsP2-
Si2: C, 45.06; H, 7.94. Found: C, 45.39; H, 7.67. 1H NMR
(300 MHz, C6D6, 20 °C): δ 0.25 (s, 9H, SiMe3), 0.34 (s, 9H,
SiMe3), 1.05 (dvt, J H-H ) 6.6 Hz, N ) 12.9 Hz, 18H, PCH-
(CH3)2), 1.33 (dvt, J H-H ) 6.9 Hz, N ) 14.1 Hz, 18H, PCH-
(CH3)2), 2.69 (m, 6H, PCH(CH3)2), 5.31 (d, J H-H ) 18.3 Hz,
1H, Os-C(CHdCHSiMe3)dCHSiMe3), 7.01 (s, 1H, Os-C(CHd
CHSiMe3)dCHSiMe3), 7.43 (d, J H-H ) 18.3 Hz, Os-C(CHd
CHSiMe3)dCHSiMe3). 13C{1H} NMR (75 MHz, C6D6, 20 °C):
δ 0.86 (s, SiMe3), 1.94 (s, SiMe3), 19.36, 20.86 (both s, PCH-
(CH3)2), 24.25 (t, N ) 12.9 Hz, PCH(CH3)2), 119.42 (s, Os-
C(CHdCHSiMe3)dCHSiMe3), 133.70 (t, J P-C ) 2.6 Hz, Os-
C(CHdCHSiMe3)dCHSiMe3), 164.16 (s, Os-C(CHdCHSiMe3)d
CHSiMe3), 176.10 (t, J P-C ) 10.1 Hz, Os-C(CHdCHSiMe3)d
CHSiMe3), 179.84 (t, J P-C ) 7.2 Hz, Os-CO), 182.99 (t, J P-C
) 7.2 Hz, Os-CO). 31P{1H} NMR (121 MHz, C6D6, 20 °C): δ
2.9 (s). IR (Nujol, cm-1): ν(CO) 1998 (s), 1919 (s); ν(CdC) 1577
(m), 1525 (m). IR (C6D6, cm-1): ν(CO) 1998 (s), 1921 (s).
[Ru {η3-(Me3Si)CHdC-CHdCH(SiMe3)}(CO)(P tBu 2Me)2]-
[BAr ′4], 6. Meth od A. RuH(OTf)(CO)(PtBu2Me)2 (0.5 g, 0.83
mmol) and NaBAr′4 (0.73 g, 0.83 mmol) were mixed in
fluorobenzene (10 mL) and stirred for 5 min. To the slurry
was added HCtCSiMe3 (0.25 mL, 1.8 mmol) via syringe. The
orange color of the mixture immediately turned dark brown.
The mixture was stirred for 30 min and filtered through a
Celite pad. The residue was washed with fluorobenzene. The
filtrate was evaporated to dryness to give a brown residue,
which was recrystallized from fluorobenzene layered with
pentane. Yield: 1.0 g (80%).
linear abs coeff (cm-1
min 2θ (deg)
max 2θ (deg)
no. of reflns collected
)
6
45
8430
4759
293
4658
4072
0.047
no. of unique intensities
no. of refined params
no. with F > 0.0
no. with F > 2.33σ(F)
R for averaging
final residuals
R(F)b
0.0463
0.0434
0.0277
0.0255
1.207
0.03
Rw(F)c
goodness of fit for last cycle 1.878
max ∆/σ for last cycle
0.06
a
b
Graphite monochromator. R ) ∑|Fo| - |Fc|/∑|Fo|. c Rw
)
2
d
[∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2, where w ) 1/σ2(|Fo|). Diffractometer
details: Huffman, J . C.; Lewis, L. N.; Caulton, K. G. Inorg. Chem.
1980, 19, 2755.
(vt, N ) 5.1 Hz, 6H, PCH3), 5.04 (dm, J H-H ) 2.1 Hz, 1H, Ha),
5.84 (d, J H-H ) 18 Hz, 1H, Hc), 6.10 (dm, J H-H ) 18H, 1H,
Hb), 7.57 (br, s, para-H of BAr′4), 7.77 (br, s, 8H, ortho-H of
BAr′4). 13C{1H} NMR (75.4 MHz, CD2Cl2, 20 °C): δ -0.18 (s,
SiMe3), 0.005 (s, SiMe3), 8.9 (vt, N ) 11.3 Hz, PCH3), 28.2 (s,
PC(CH3)), 29.4 (s, PC(CH3)), 38.3 (vt, N ) 9 Hz, PCMe3), 39.9
(vt, N ) 9.1 Hz, PCMe3), 98.8 (s, CHc), 110.9 (s, CHb), 118.1
(m, 4-C of BAr′4), 125.2 (q, J C-F ) 271 Hz, CF3), 128.4 (s, CHa),
129.1 (q of m, J C-F ) 40.2 Hz, 3 and 5 C of BAr′4), 135.4 (s, 2
and 6 C of BAr′4), 163.9 (t, Ru-CdC), 204 (t, CO). 31P{1H}NMR
(121 MHz, CD2Cl2, 20 °C): δ 38.6 (s). 19F NMR (282 MHz,
CD2Cl2, 20 °C): δ -62.0 (s). IR (Nujol, cm-1): ν(CO) 1961.
X-r a y Str u ctu r e Deter m in a tion s. (a ) OsCl{(E)-CHd
CHSiMe3}-(dCdCHSiMe3)(P iP r 3)2. For C28H63ClOsP2Si2 at
-170 °C, a ) 7.961(1) Å, b ) 10.710(1) Å, c ) 20.697(3) Å, â
) 90.10(1)° with Z ) 2 in space group P21; R(F) ) 0.0277 for
2178 observed reflections. The X-ray quality crystals were
grown by cooling a solution of the compound in pentane at
-40 °C. A larger crystal was cleaved to obtain a suitable sized
fragment, which was affixed to the end of a glass fiber using
silicone grease. The mounted crystal was transferred to the
goniostat, where it was cooled to -170 °C for characterization
and data collection (Table 1). The data were collected using a
standard moving crystal-moving detector technique with fixed
backgrounds at each extreme of the scan. Data were corrected
for Lorentz and polarization effects. Based on the measured
dimensions of the crystal, an analytical absorption correction
was applied and equivalent reflections averaged. Despite
initial indications of orthorhombic symmetry, successful solu-
tion and refinement of the structure were only possible in a
monoclinic setting. During refinement it became obvious that
the vinyl and vinylidene ligands were mutually disordered.
The four carbon atoms all refined to nonpositive definite
thermal parameters when allowed to vary anisotropically. At
this point hydrogen atoms were fixed, the four carbon atoms
mentioned were refined isotropically, and all the other atoms
were allowed to vary anisotropically. The final cycles of
refinement consisted of fixed hydrogen atoms, isotropic pa-
rameters for the four disordered half-carbons bonded to the
metal and two carbon atoms adjacent to the disorder, and
Meth od B. [RuH(CO)(PtBu2Me)2][BAr′4] (10 mg, 7.6 × 10-3
mmol), 5, was dissolved in CD2Cl2 (0.5 mL). To this solution
was added HCtCSiMe3 (2.3 µL, 1.6 × 10-2 mmol) via syringe.
The solution color changed immediately from orange to brown.
1H and 31P{1H} NMR spectroscopies reveal clean formation of
[Ru{η3-(Me3Si)CHdC-CHdCH(SiMe3)}(CO)(Pt Bu2Me)2]-
[BAr′4]. Anal. Calcd for C61H67BF24OP2RuSi2: C, 48.77; H,
4.50. Found: C, 48.35; H, 4.80. 1H NMR (300 MHz, CD2Cl2,
20 °C): δ 0.34 (s, 9H, SiMe3), 0.43 (s, 9H, SiMe3), 1.15 (vt, N
) 13.5 Hz, 18H, PtBu), 1.25 (vt, N ) 14.1 Hz, 18H, PtBu), 1.62

4702 Organometallics, Vol. 17, No. 21, 1998
Huang et al.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for OsCl(CHCHSiMe3)(CCHSiMe3)(P iP r 3)2
Os(1)-Cl(2)
Os(1)-P(3)
Os(1)-P(13)
Os(1)-C(23)
2.416(3)
2.397(5)
2.403(5)
1.92(3)
Os(1)-C(29)
C(23)-C(24)
C(29)-C(30)
1.82(3)
1.45(3)
1.32(3)
Cl(2)-Os(1)-P(3)
Cl(2)-Os(1)-P(13)
Cl(2)-Os(1)-C(23)
Cl(2)-Os(1)-C(29)
P(3)-Os(1)-P(13)
P(3)-Os(1)-C(23)
88.3(3)
88.2(3)
121(1)
141(1)
176.5(1)
90(1)
P(3)-Os(1)-C(29)
P(13)-Os(1)-C(23)
P(13)-Os(1)-C(29)
C(23)-Os(1)-C(29)
Os(1)-C(23)-C(24)
Os(1)-C(29)-C(30)
95(1)
92(1)
88(1)
97(1)
139(2)
171(2)
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for
+
Ru [(Me3Si)CHdC-CHdCH(SiMe3-)](CO)(P tBu 2Me)2
in its B[C6(CF 3)2H3]4 Sa lt
Ru(1)-P(2)
Ru(1)-P(12)
Ru(1)-C(27)
Ru(1)-C(28)
Ru(1)-C(34)
Ru(1)-C(4)
2.393(3)
2.499(3)
2.28(1)
2.01(1)
1.84(1)
2.943
Ru-C(26)
2.57(1)
1.16(1)
1.40(2)
1.45(1)
1.31(1)
O(35)-C(34)
C(26)-C(27)
C(27)-C(28)
C(28)-C(29)
F igu r e 1. ORTEP drawing of Os[CCH(SiMe3)][CHCH-
(SiMe3)]Cl(PiPr3)2. Only the vinyl and vinylidene hydrogens
are shown.
P(2)-Ru(1)-P(12)
P(2)-Ru(1)-C(34)
159.70(9) Ru(1)-P(2)-C(11)
112.8(3)
90.0(3)
Ru(1)-P(12)-C(13) 115.5(3)
Ru(1)-P(12)-C(17) 117.9(3)
Ru(1)-P(12)-C(21) 106.1(3)
P(12)-Ru(1)-C(28) 101.6(3)
P(12)-Ru(1)-C(34)
Ru(1)-P(2)-C(3)
Ru(1)-P(2)-C(7)
85.5(3)
99.6(3)
123.9(3)
anisotropic parameters for the remaining atoms. The absolute
configuration reported here refined to significantly lower
residuals than its enantiomer. No significant changes in the
structure were found in a purely isotropic refinement. A final
difference Fourier was featureless, the largest peak being 1.21
e/A3. Results of the structure determination are shown in
Table 2 and Figure 1. We have refined the structure of OsCl-
(-CHdCHSiMe3)(dCHdCHSiMe3)(PiPr3)2 in the orthorhombic
space group P22121 (http://www.iumsc.indiana.edu/cgi-bin/
getinfo.pl/98405). The results do not significantly change any
of the structural parameters, and the molecule still suffers
from the same disorder as reported in the P21 space group.
The residual in P21 is lower (R ) 0.027 vs 0.034). The fact
remains that the beta angle is not 90°: it was determined to
be 90.10(1)° based on two independent sets of data, and the
diffractometer alignment was verified after the measurements
were taken.
F igu r e 2. ORTEP drawing of the nonhydrogen atoms of
Ru[(Me3Si)HCdC-CHdCH(SiMe3)](CO)(PtBu2Me)2
.
+
idealized positions, and only nonmethyl hydrogens were al-
lowed to vary isotropically in the final refinement. A final
difference Fourier was essentially featureless, the largest
peaks being less than 0.6 e/A3. Results of the structure
determination are shown in Table 3 and Figure 2. When we
refined the structure of the ruthenium compound with all
carbons isotropic, to have a better data-to-parameter ratio
(http://www.iumsc.indiana.edu/cgi-bin/getinfo.pl/98404), there
were no significant differences (e1 esd) in the structure.
Com p u ta tion a l Deta ils. Ab initio calculations were car-
ried out with the Gaussian 94 set of programs within the
framework of DFT at the B3LYP level.6 LANL2DZ effective
core potential (quasi relativistic for the metal centers) was used
to replace the 28 innermost electrons of Ru, the 46 innermost
electrons of Os, and the 10 core electrons of P, Cl, and Si. The
LANL2DZ basis set was used for all atoms but the H of PH3,
which were represented at the STO-3G level. Polarization
functions have been added only to all C and C-bonded H’s. Full
geometry optimization was performed with no symmetry
restriction.
(b )
[R u {η3-(Me 3Si)CH dC-CH dCH (SiMe 3)}(CO)-
(P tBu 2Me)2][BAr ′4]. For C61H75BF24OP2RuSi2 at -178 °C, a
) 24.056(2) Å, b ) 18.440(2) Å, c ) 15.789(1) Å with Z ) 4 in
space group Pna21; R(F) ) 0.0463 for 4072 observed data. The
X-ray quality crystals were grown by layering the solution of
the compound in CH2Cl2 with pentane at -20 °C. A well-
formed orange crystal was pipetted from the recrystallization
media, dried, and affixed to the end of a glass fiber using
silicone grease. The crystal was then transferred to the
goniostat, where it was cooled to -170 °C for characterization
and data collection (Table 1). Standard inert atmosphere
techniques were used during handling. A systematic search
of a limited hemisphere of reciprocal space located a set of
diffraction maxima with orthorhombic symmetry correspond-
ing to the space group Pna21 or Pnam. Subsequent solution
and refinement confirmed the former choice. Data were
collected using a continuous θ, 2θ scan with fixed background
counts at each extreme of the scan. Equivalent data were
averaged after Lorentz and polarization effects were applied.
The structure was readily solved by direct methods (SHEXTL-
PC) and standard Fourier techniques. Most hydrogen atoms
were located in a difference Fourier phased on the nonhydro-
gen atoms and were included in the final least-squares
refinement. Hydrogen atoms on several of the methyl groups
did not converge properly, so all hydrogens were placed in fixed
(6) 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.; Peterson, G.
A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski,
V. G.; Ortiz, J . V.; Foresman, J . B.; Ciolowski, J .; Stefanov, B. B.;
Nanayakkara, A.; Challacombre, 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. I; Gaussian, Inc.: Pittsburgh, PA, 1995.

CO-Induced C(sp2)/ C(sp) Coupling on Ru and Os
Organometallics, Vol. 17, No. 21, 1998 4703
Sch em e 1
(139(2)°) and Os-C(29)-C(30) (171(2)°) angles compare
well with the ones found in other osmium-vinyl8b,9 and
osmium-vinylidene complexes.10 Vinyl-vinylidene com-
plexes have been proposed as intermediates in reactions
of alkyne coupling11 and also have been isolated in some
cases.12 As far as we know, compound 3 constitutes the
first structurally characterized compound of this kind.
P r ep a r a tion a n d Ch a r a cter iza tion of OsCl{C-
(CHdCHSiMe3)dCHSiMe3}(CO)2(P iP r 3)2, 4. Carbon
monoxide induces migration of the vinyl ligand to the
R-carbon atom of the vinylidene to give the vinyl
derivative 4 (eq 2). The IR spectrum of 4 in C6D6 shows
Resu lts
P r ep a r a tion a n d Ch a r a cter iza tion of OsCl{(E)-
CHdCHSiMe3}(dCdCHSiMe3)(P iP r 3)2, 3. Trimeth-
ylsilylacetylene inserts in the Os-H bond of OsHCl(d
CdCHSiMe3)(PiPr3)2 (2) giving the vinyl-vinylidene
complex OsCl{(E)-CHdCHSiMe3}(dCdCHSiMe3)(Pi-
Pr3)2 (3). Alternatively, this compound can be prepared
by reaction of OsH3Cl(PiPr3)2 (1) with HCtCSiMe3 in a
two CO stretching frequencies of similar intensity at
1998 and 1921 cm-1, in accord with a cis-disposition of
both ligands. 1H NMR spectrum shows three reso-
nances for the three vinylic protons at 5.31, 7.01, and
7.43 ppm. The 13C{1H} NMR spectrum shows, in
addition to two triplets corresponding to the carbonyl
ligands (179.84, 182.99 ppm), four peaks at 119.42,
133.70, 164.16, and 176.10 ppm assigned to the carbon
atoms of the vinyl ligand by comparison with reported
chemical shifts on related rhodium complexes.12c
Reaction of 3 with equimolar carbon monoxide yields
a mixture of unreacted 3 and the dicarbonyl complex 4.
This means that any 1:1 CO adduct reacts more rapidly
with CO than does 3 itself.
1
molar ratio 1:3 (Scheme 1). The H NMR spectrum of
3 shows the peak corresponding to the proton on the
â-carbon atom of the vinylidene ligand at -0.11 as a
doublet of triplets by coupling with both phosphines and
with the R-proton of the vinyl ligand (confirmed by
means of a COSY experiment), and although this
coupling through five bonds is unusual, long-distance
coupling (up to nine bonds) can be observed in highly
conjugated organic systems.7 This proton is shifted to
a very high field, as a consequence of the combination
of the electron richness of the metal and the electron-
donating group Me3Si attached to the â-carbon atom of
the vinylidene. The vinylic protons appear at 8.53 as a
doublet of doublets (HR, coupling with the other vinylic
proton and with the vinylidene proton) and 4.79 ppm
as a doublet of triplets (Hâ, coupling with both phos-
phines and the R-proton of the vinyl ligand). The 13C-
{1H} NMR spectrum displays, in addition to the signals
corresponding to the phosphines, four triplets assigned
to the vinylidene (272.33, 87.19 ppm, CR and Câ,
respectively) and vinyl (153.99, 130.87 ppm, CR and Câ,
respectively) carbon atoms. They appear in the typical
range described before for these ligands and deserve no
further comment.
The single-crystal X-ray structure of 3 reveals a
distorted trigonal bipyramid (Y shape, considering the
vinyl, vinylidene, and Cl ligands, Figure 1) with the
phosphines in apical positions and the other three
ligands on the equatorial plane. The majority of struc-
turally characterized five-coordinate d6 complexes with
σ-donor and π-acceptor ligands are square-based pyra-
midal.8 The Cl-Os-C(29) angle (141.5(11)°) is over 20°
smaller than any basal angle in a square pyramid
previously observed.8 Due to the spatial similarity of
both ligands, there is disorder between vinyl and
vinylidene groups, but despite this, the Os-C(23)-C(24)
Reaction of [Ru H(CO)(P tBu 2Me)2][BAr ′4] (5) with
Tr im eth ylsilyla cetylen e. Addition of 2 equiv of HCt
CSiMe3 to a CD2Cl2 solution of 5 causes an immediate
color change from orange to deep brown. NMR analysis
of the mixture reveals a clean reaction to give a product
that shows only one broad (ν1/2 ) 65 Hz) singlet in the
31P{1H} NMR spectrum and a sharp singlet in the 19F
NMR spectrum. In the vinyl region of the 1H NMR
spectrum there are three types of peaks with equal
intensity at 6.10 (doublet of multiplets), 5.84 (doublet),
and 5.04 ppm (doublet of multiplets). In the phosphine
tBu region two virtual triplets are seen at 1.25 and 1.15
(8) (a) Bohanna, C.; Esteruelas, M. A.; Lahoz, F. J .; On˜ate, E.; Oro,
L. A. Organometallics 1995, 14, 4685. (b) Werner, H.; Esteruelas, M.
A.; Otto, H. Organometallics 1986, 5, 2295. (c) Huang, D.; Heyn, R.
H.; Bollinger, J . C.; Caulton, K. G. Organometallics 1997, 16, 292. (d)
Poulton, J . T.; Sigalas, M. P.; Folting, K.; Streib, W. E.; Eisenstein,
O.; Caulton, K. G. Inorg. Chem. 1994, 33, 1476. (e) Esteruelas, M. A.;
Liu, F.; On˜ate, E.; Sola, E.; Zeier, B. Organometallics 1997, 16, 2919.
(f) Huang, D. Unpublished results.
(9) Werner, H.; Weinand, R.; Knaup, W.; Peters, K.; von Schnering,
H. G. Organometallics 1991, 10, 3967.
(10) (a) Pourreau, D. B.; Geoffroy, G. L.; Rheingold, A. L.; Geib, S.
J . Organometallics 1986, 5, 1337. (b) Weber, B.; Steinert P.; Wind-
mu¨ller, B.; Wolf, J .; Werner, H. J . Chem. Soc., Chem. Commun. 1994,
2595. (c) Roper, W. R.; Waters, J . M.; Wright, L. J .; van Meurs, F. J .
Organomet. Chem. 1980, 201, 27.
(11) (a) Selnau, H. E.; Merola, J . S. J . Am. Chem. Soc. 1991, 113,
4008. (b) Braun, T.; Meuer, P.; Werner, H. Organometallics 1996, 15,
4075.
(12) (a) Wiedemann, R.; Steinert, P.; Scha¨fer, M.; Werner, H. J . Am.
Chem. Soc. 1993, 115, 9864. (b) Wiedemann, R.; Wolf, J .; Werner, H.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1244. (c) Werner, H.; Wiede-
mann, R.; Steinert, P.; Wolf, J . Chem. Eur. J . 1997, 3, 127.
(7) J ackman, L. M.; Sternhell, S. In Applications of Nuclear Magnetic
Resonance Spectroscopy in Organic Chemistry, 2nd ed.; Barton, D. R.
H., Doering, W., Eds.; Pergamon Press: New York, 1969; p 328.

4704 Organometallics, Vol. 17, No. 21, 1998
Huang et al.
t
ppm, indicating that the two Bu groups in the trans
When the metal has a better back-donating ability, as
in Cp′Ru(L)(RR1CdCR2CdCR3R4) (Cp′ ) Cp or Cp*, L
) phosphine), the butadienyl ligand is bonded to the
metal more symmetrically (i.e., allyl).15 The dihedral
angle of the plane defined by the C(27)-C(28)-C(29)
and the plane C(26)-C(27)-C(28) is 54.2°; therefore, the
butadienyl ligand is twisted, as in other butadienyl
complexes.14,16
phosphine ligands are diastereotopic. In the SiMe3
region two singlets with the same intensity are found
at 0.34 and 0.43. Therefore, the organometallic product
contains the coupled unit from two alkyne molecules.
The definitive structure of the product comes from the
X-ray crystal structure analysis (vide infra). Single
crystals were grown from a CH2Cl2 solution of 6
(prepared more conveniently directly from RuH(OTf)-
(CO)(PtBu2Me)2, NaBAr′4, and HCtCSiMe3) layered
with pentane (eq 3). The ORTEP diagram is depicted
Coupling of alkynyl (C2R) and vinylidene (CCHR)
ligands on Ru or Os has been reported earlier.16-21
However, this gives an R2HC4 ligand, which is 2 H more
oxidized than our R2H3C4 ligands here (from vinylidene
and vinyl). Comparisons are therefore limited.
The lack of symmetry of the butadienyl ligand de-
stroys any symmetry relationship between the phos-
phorus nuclei, even if (as is reasonable) the agostic
interaction is rapidly fluxional at 25 °C between the two
phosphines. It is thus significant that the 31P{1H} NMR
spectrum shows only a singlet at 25 °C. However, at
-70 °C, the 31P{1H} NMR spectrum is an AM pattern
2
(two doublets) with a J P-P of 203 Hz, consistent with a
large angle P-Ru-P. Since the barrier to agostic
fluxionality is expected to be very low, we attributed
this decoalescence to freezing out of some fluxionality
that gives the Ru/butadienyl unit mirror symmetry. We
propose that this is the process in eq 4, which is
conversion to the η1-butadienyl, which is, in fact,
conversion to an η1-vinyl. Note that, throughout this
in Figure 2.
This shows that two alkynes have had one H added
from Ru and they have been coupled through one carbon
to give a butadienyl ligand Me3Si(H)CdCH-CdCH-
(SiMe3); this ligand is η3-bound to the Ru and can be
thought of as occupying two coordination sites on the
metal. One dCH(SiMe3) group does not interact with
the metal. The geometry of this complex can be viewed
as a distorted octahedron with one site occupied by an
agostic interaction from the tBu group of one phosphine
ligand. The agostic Ru-C(4) distance is 2.943 Å. This
agostic interaction shortens the Ru-P(2) bond (agostic)
significantly (0.1 Å compared to the other Ru-P bond).
Moreover, the Ru-P(2)-C(3) angle (99.6°) is compressed
from the normal Ru-P-C angles (115°). These struc-
tural parameters are similar to those found in RuH-
t
rearrangement, the Bu groups on the phosphine are
predicted to remain diastereotopic; indeed they still
1
show two H NMR chemical shifts at 25 °C, when the
fluxionality of eq 4 is fast.
(CO)(PtBu2Me)2+,3 RuPh(CO)(PtBu2Me)2+,2 and Ir(H)2(Pt-
+ 13
Bu2Ph)2
.
However, the Ru-C(4) distance (2.943 Å)
is slightly longer than in the above formal 14 e-
RuH(CO)(PtBu2Me)2+, suggesting marginally weaker
agostic interaction. The strong deviation of linearity of
the P-Ru-P angle (159.7°) could not be entirely due to
the agostic interaction, since it may also be attributed
to the steric repulsion between the Me3Si of the buta-
dienyl ligand and the tBu groups of the phosphine
ligands. Trans to C(4), the σ-bound butadienyl carbon
(C(28)) is 2.013 Å away from Ru. This distance is much
shorter than that of the π-coordinated ones (C(26) and
C(27), 2.568 and 2.277 Å, respectively). Therefore, the
complex is best viewed as a σ-π allyl with the σ bond
localized on C(28). Wakatsuki and co-workers reported
a closely related complex, RuCl{η3-Me3SiCHdCCHd
CHSiMe3}(CO)(PPh3)2 (prepared from RuHCl(CO)(P-
Ph3)3 and Me3SiCtCCHdCHSiMe3).14 In this complex,
the butadienyl ligand also coordinates in σ,π mode with
different bond lengths of Ru-C(σ) (2.044 Å) and RuC-
(π) (2.627 and 2.336 Å, respectively). These distances
appear to be longer than that of 6 (0.04 Å for Ru-C(σ)
and 0.06 Å for Ru-C(π)). Apparently, the formally 16-
electron cationic complex, 6, has a more electron-
deficient Ru(II) center and thus binds ligands stronger.
Com p a r ison . In summary, there is no C-C coupling
in vinyl vinylidene complex 3, although η3 binding of
the newly formed unsaturated ligand could give an
acceptable electron count. However, coordination of CO
to osmium triggers C-C coupling (i.e., vinyl carbon
migration to the vinylidene CR), but the resulting
unsaturated ligand remains monohapto bonded to Os.
Moreover, the five-coordinate η1-hydrocarbon monocar-
bonyl complex does not remain unsaturated but adds a
second CO to adopt a six-coordinate, saturated form.
In the case of the cationic ruthenium monocarbonyl,
terminal alkyne inserts in the Ru-H bond, then couples
to a second alkyne to form a complex with the same
butadienyl ligand as in 4, but now η3-attached to Ru.
Ruthenium is sufficiently electrophilic in its [Ru{η3-Me3-
SiHCdC-CHdCHSiMe3}(CO)(PtBu2Me)2]+ form that
t
one Bu group is required to agostically donate to the
(14) (a) Wakatsuki, Y.; Yamazaki, H.; Maruyama, Y.; Shimizu, I.
J . Organomet. Chem. 1992, 430, C60. (b) Wakatsuki, Y.; Yamazaki,
H. J . Organomet. Chem. 1995, 500, 349.
(15) (a) Yi, C. S.; Liu, N.; Rheingold, A. L.; Liable-Sands, L. M.
Organometallics 1997, 16, 3910. (b) Bruce, M. I.; Duffy, D. N.; Liddell,
M. J .; Tiekink, E. R. T.; Nicholson, B. K. Organometallics 1992, 11,
1527.
(13) Cooper, A. C.; Streib, W. E.; Eisenstein, O.; Caulton, K. G. J .
Am. Chem. Soc. 1997, 119, 9069.
(16) Yi, C. S.; Liu, N. Organometallics 1996, 15, 3968, and references
therein.

CO-Induced C(sp2)/ C(sp) Coupling on Ru and Os
Organometallics, Vol. 17, No. 21, 1998 4705
of the disorder on the resolution of the geometry of 3 in
the X-ray study. The vinyl and vinylidene groups both
lie in the molecular mirror plane. The complex has a
distorted trigonal bipyramidal geometry with a small
angle between the vinylidene and the vinyl groups
(C(2)-Os-C(3) ) 96.3° which compares well to the
experimental value (97.0˚)). The chlorine is not sym-
metrically positioned with respect to the two ligands
(C(2)-Os-Cl ) 141.2° and C(3)-Os-Cl ) 122.5°,
compared with the experimental results, 141.5° and
121.4°, respectively). The vinyl Os-C(3)-C(4) angle is
quite open (136.8°), and the vinylidene is slightly
nonlinear (Os-C(2)-C(1) ) 173.2°). The two phos-
phines are essentially trans to each other as they are
in 3 (178.6°). It has been verified that rotating the vinyl
group by 180° and thus putting the H of C(3) between
the vinyl and vinylidene ligands does not create a
minimum.
F igu r e 3. Optimized geometries and relative energies
(kcal‚mol-1) for isomeric Ru and Os complexes; H’s of PH3
have been removed for clarity. See text for abbreviations.
metal, giving a “lightly stabilized” 18-electron complex.
Obviously, 6 must be formed through a vinyl vinylidene
intermediate similar to complex 3.22
The agreement between the solid-state structure of
6 and the calculated BTRu model is also very good but
will illustrate a larger influence of the steric factors
between the butadienyl ligand and the large phosphine
ligands used experimentally. The complex is a distorted
octahedron with a missing site trans to C(2). The
butadienyl ligand is η3-bonded to the metal and is thus
strongly twisted (C(1)-C(2)-C(3)-C(4) ) 56.2° com-
pared to the experimental 54.3°). The C(2) center is
closer to the metal (Ru-C(2) ) 2.041 Å), while the
distance of C(3) and C(4) to the metal are 2.344 and
2.595 Å, respectively. Bond alternation is apparent in
the butadienyl ligand (C(1)-C(2) ) 1.324 Å, C(2)-C(3)
) 1.450 Å, C(3)-C(4) 1.371 Å), which compares well to
the experimental corresponding values, 1.309, 1.445,
and 1.397 Å. As expected, coordination to the metal
makes the C(3)-C(4) double bond longer than C(1)-
C(2). However, C(3)-C(4) is shorter than the average
distance found in coordinated double bonds, an ad-
ditional proof of the weak coordination.23 Since the
butadienyl ligand is mostly bonded to the metal through
the Ru-C(2) σ bond, one can view this complex as a 16-
electron unsaturated species with a strong σ-donor
ligand C(2) and a weaker donor C(3)-C(4) π bond. A
square-pyramidal geometry with C(2) at the apical site
of the pyramid is thus preferred. This strong bond to
the center of the butadienyl ligand has already been
addressed by ab initio calculations.14
Since the butadienyl ligand is considerably twisted,
some part of it is close to the phosphine ligands. This
induces geometrical distortions to decrease those repul-
sions. Thus, while the phosphines are essentially trans
in BTRu , they are significantly moved away from linear-
ity in the experimental complex (159.7°). The presence
of SiH3 on C(1) and C(4) in the model complex BTRu Si
is not sufficient to mimic the steric interactions since
the calculated P-Ru-P angle there is equal to 173.8°.
The bulk of the phosphine ligands are responsible for
their deviation away from linearity.
The geometry of BTOs shows a significant influence
of the metal fragment on the bonding mode of the
butadienyl fragment. The η3 bonding mode is more
apparent with almost equal distance between Os and
C(2), C(3) and C(4). Thus, the system cannot now be
Com p u ta tion a l Stu d y. Optimization of Ru(CO)-
+
(C4H5)(PH3)2 and OsCl(C4H5)(PH3)2 reveals the exist-
ence of two minima, one of which has the structure of a
vinyl vinylidene (VV) complex and the other has the
structure of the butadienyl (BT) complex. For Ru(CO)+,
the BT isomer (BTRu ) is more stable than the VV
(VVRu ) isomer by 35.3 kcal‚mol-1, while in the case of
OsCl, BTOS is more stable than VVOs by only 8.3
kcal‚mol-1. The important feature of these calculations
is that the marked preference for the butadienyl com-
plex has decreased by 27 kcal‚mol-1 on going from the
Ru(CO)+ group to the OsCl group. As will be apparent
from the discussion of the geometries, the steric interac-
tions from the phosphines will be considerably more
important for the butadienyl complex, whose stability
is thus overestimated by the modeling of the phosphine
ligands as PH3. The energy pattern thus reflects well
that VVOs and BTRu are the two experimentally ob-
served structures.
The structures of BTRu , BTOs, VVRu , and VVOs are
shown in Figure 3. Since the influence of silyl groups
on the butadienyl structure was not clear, the structure
of [Ru(CO){(H3Si)C(H)dCH-CdC(H)(SiH3)}(PH3)2]+,
BTRu Si, has been optimized at the same level of theory
as BTRu . Since no significant geometrical difference
was obtained between BTRu Si and BTRu , only the latter
will be discussed.
The structure of VVOS also agrees with the solid-state
structure of 3 and shows the lack of significant influence
(17) Hill, A. F. In Comprehensive Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: New York, 1995;
Vol. 7.
(18) Slugovc, C.; Mereiter, K.; Zobetz, E.; Schmid, R.; Kirchner, K.
Organometallics 1996, 15, 5275.
(19) Gemel, C.; Kickelbick, G.; Schmid, R.; Kirchner, K. J . Chem.
Soc., Dalton Trans. 1997, 2113.
(20) (a) Barbaro, P.; Bianchini, C.; Peruzzini, M.; Polo, A.; Zanobini,
F.; Frediani, P. Inorg. Chim. Acta 1994, 220, 5. (b) Bianchini, C.;
Peruzzini, M.; Zonobini, F.; Frediani, P.; Albinati, A. J . Am. Chem.
Soc. 1991, 113, 5453. (c) Wakatsuki, Y.; Yamazaki, H.; Kumegawa,
N.; Satoh, T.; Stoh, J . Y. J . Am. Chem. Soc. 1991, 113, 9604.
(21) (a) Hughes, D. L.; J iminez-Tenorio, M.; Leigh, G. J .; Rowley,
A. T. J . Chem. Soc., Dalton Trans. 1993, 3151. (b) Hills, A.; Hughes,
D. L.; J iminez-Tenorio, M.; Leigh, G. J .; McGeary, C. A.; Rowley, A.
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Commun. 1991, 522.
(22) Detailed mechanism of this reaction will be reported in
separate paper.
a
(23) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1.

4706 Organometallics, Vol. 17, No. 21, 1998
Huang et al.
considered as a 14-electron d6 ML4 complex weakly
stabilized by an additional metal-π-bond interaction.
It is a truly 16-electron complex, and its geometry is
best understood by analogy with d6 ML5 considering
that the allylic part of the butadienyl ligand is in fact a
bidentate ligand donating σ and π electrons to the metal.
Due to the presence of a π donor, the structure has a Y
shape with almost equal Cl-Os-C(2) and Cl-Os-C(4)
angles. The distances within the butadienyl fragment
factors, while the large difference in the case of Ru(CO)+
permits the more sterically hindered structure to remain
preferable.
The small difference in energy in the case of Os
suggests that it should be possible to go from the VV
structure to the BT structure. The activation barrier
for intramolecular rearrangement has not been calcu-
lated, but related results for the transformation of Os
hydrido carbyne into Os carbene complex involving the
migration of H show it to be promoted by an incoming
ligand.25 This is the case also in the present study, since
the addition of CO to VVOs results in the coupling of
C(2) and C(3). The complex does not stop at the BTOs
structure but incorporates one more CO to give product
4.
have also been modified with respect to BTRu
. The
C(2)-C(3) and C(3)-C(4) are almost equal, which
indicates full delocalization of the four electrons of the
ligand. The dihedral angle C(4)-C(3)-C(2)-C(1) is
46.7°, which is close to that in BTRu
.
The structure of VVRu is also different from that of
VVOS. As expected from the lack of π-donor ligand in a
pentacoordinated d6 ML5 system, a square-pyramidal
geometry is preferred for VVRu . To prevent competition
between the π-accepting capability of vinylidene and
CO, these ligands go cis and the former ligand takes
the apical site in VVRu . There is no drastic difference
in the geometry within the vinyl or the vinylidene
Con clu sion
Oxidatively induced reductive elimination (eq 5) is a
reaction type of some generality, being the way a
transformed organic ligand can be recovered from a
transition metal (e.g., CeIV for arene complexes). Such
oxidation can also be effected by olefins containing
electron-withdrawing groups (e.g., tetracyanoethylene,
esters, or acrylonitrile). The results reported here are
qualitatively similar in that they represent reductive
coupling (but not elimination from the coordination
sphere), triggered by an electron-withdrawing ligand
CO. In the absence of a carbonyl ligand, and influenced
by the σ-donor ligand Cl, OsCl{(E)-CHdCHSiMe3)(dCd
CHSiMe3)L2 has no coupling of the two hydrocarbyl
ligands and Os is in the oxidation state IV. In the case
of the less easily oxidized 4d element Ru, and with a
π-acid ligand CO (and thus a positive charge), reductive
coupling occurs rapidly, to give the butadienyl ligand.
For Os, coordination of two electron-withdrawing car-
bonyl ligands to 3 finally triggers reductive C-C
coupling.
between VVRu and VVOs
.
What then is the reason for the large difference in
energy between the two isomers for OsCl and RuCO+
since all four are 16-electron complexes, which are either
square-pyramidal or Y-shaped species?24 Energy change
from T to Y geometries involves a few kcal‚mol-1 and
cannot justify the big energy difference.23,24 Thus, there
is an intrinsic preference for making a C-C bond in the
Ru complex, while there is an intrinsic preference for
ligands with strong π-accepting capability in the case
of Os. Os is a better electron donor and therefore
prefers a structure with back-bonding capability. Ru
is intrinsically a poorer donor, and its electron-donating
ability is diminished by the presence of a π-acceptor
ligand. A structure with more CC bonds is thus favored.
This interpretation neglects the σ effects, which will
involve comparing M-C bond energy to CC bond ener-
gies. Our point of view is probably a simplification of
all of the effects. The calculations indicate, however,
that the BT structure is favored, even for OsCl. It is
clear that the lack of planarity of the butadienyl ligand
induces large steric effects which are absent in the VV
isomer. The small difference in energy between VV and
BT in the case of OsCl is easily overcome by the steric
Ack n ow led gm en t. This work was in part supported
by an international grant for U.S./France collaboration
(NSF/CNRS (PICS)). O.E. thanks E. R. Davidson for a
generous donation of computational time. M.O. thanks
the Spanish Ministerio de Educacio´n y Cultura for a
postdoctoral fellowship. J ohnson Matthey/Aesar is
thanked for material support.
Su p p or t in g In for m a t ion Ava ila b le: Full crystallo-
graphic data and bond lengths and angles for two compounds
(16 pages). Ordering information is given on any current
masthead page.
(24) (a) J ean, Y.; Eisenstein, O. Polyhedron 1988, 7, 405. (b) Rachidi,
I. E.-I.; Eisenstein, O.; J ean, Y. New J . Chem. 1990, 14, 671. (c) Riehl,
J .-F.; J ean, Y.; Eisenstein, O.; Pe´lissier, M. Organometallics 1992, 11,
729. (d) Albinati, A.; Bakhmutov, V. I.; Caulton, K. G.; Clot, E.; Eckert,
J .; Eisenstein, O.; Gusev, D. G.; Grushin, V. V.; Hauger, B. E.; Kloster,
W.; Koetzle, T. F.; McMullan, R. K.; O′Loughlin, M.; Pe´lissier, M.; Ricci,
J . S.; Sigalas, M. P.; Vymenits, A. B. J . Am. Chem. Soc. 1993, 115,
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OM970961V
(25) Spivak, G. J .; Coalter, J . N.; Oliva´n, M.; Eisenstein, O.; Caulton,
K. G. Organometallics, in press.