Hydride is not a spectator ligand in the formation of hydrido vinylidene from terminal alkyne and ruthenium and osmium hydrides: Mechanistic differences

Article abstract of DOI:10.1021/om971109r

RuHX(H₂)L₂ (L = P^tBu₂Me; X = Cl, I) and OsH₃ClL₂ (L = PⁱPr₃) react (time of mixing) with terminal alkynes in a 1:2 stoichiometry to give MHX(=C=CHR)L₂ and RCH=CH₂. The reactions of RuHX(H₂)L₂ with PhC=CD lead to RuDX(=C=CHPh)L₂ as the only isotopomers. This result is understood in terms of an insertion of the alkyne in the Ru-H bond to make a vinyl, followed by an α-hydrogen migration, giving the hydrido/vinylidene. This reaction path has been studied by ab initio (B3LYP) calculations with location of the minima and transition states. In agreement with isotopic labeling experiments, it is shown that the path starting with insertion into the Ru-H bond is more favorable than a 1,2-migration within the coordinated alkyne ligand. The favored reaction is calculated to be exothermic from the starting compounds to intermediates and to products with the energies of all transition states well below that of the separated reactants. The mechanism involves the formation of a 14-electron η¹-vinyl intermediate which, after structural changes, gives the 16-electron hydrido/vinylidene product. The same general reaction path is calculated to be preferred for Os, but differences occur between the geometries of the vinyl intermediate (it is η²-vinyl for Os) and in the total number of intermediates involved.

Full text of DOI:10.1021/om971109r

Organometallics 1998, 17, 3091-3100
3091
Hyd r id e Is Not a Sp ecta tor Liga n d in th e F or m a tion of
Hyd r id o Vin ylid en e fr om Ter m in a l Alk yn e a n d
Ru th en iu m a n d Osm iu m Hyd r id es: Mech a n istic
Differ en ces
Montserrat Oliva´n,† Eric Clot,‡ Odile Eisenstein,*,‡ and Kenneth G. Caulton*,†
Department of Chemistry, Indiana University, Bloomington, Indiana 47405-4001, and
LSDSMS (UMR 5636), Universite´ de Montpellier 2, Case Courrier 14,
34095 Montpellier Cedex 5, France
Received December 16, 1997
RuHX(H2)L2 (L ) PtBu2Me; X ) Cl, I) and OsH3ClL2 (L ) PiPr3) react (time of mixing)
with terminal alkynes in a 1:2 stoichiometry to give MHX(dCdCHR)L2 and RCHdCH2.
The reactions of RuHX(H2)L2 with PhCtCD lead to RuDX(dCdCHPh)L2 as the only
isotopomers. This result is understood in terms of an insertion of the alkyne in the Ru-H
bond to make a vinyl, followed by an R-hydrogen migration, giving the hydrido/vinylidene.
This reaction path has been studied by ab initio (B3LYP) calculations with location of the
minima and transition states. In agreement with isotopic labeling experiments, it is shown
that the path starting with insertion into the Ru-H bond is more favorable than a 1,2-
migration within the coordinated alkyne ligand. The favored reaction is calculated to be
exothermic from the starting compounds to intermediates and to products with the energies
of all transition states well below that of the separated reactants. The mechanism involves
the formation of a 14-electron η1-vinyl intermediate which, after structural changes, gives
the 16-electron hydrido/vinylidene product. The same general reaction path is calculated
to be preferred for Os, but differences occur between the geometries of the vinyl intermediate
(it is η2-vinyl for Os) and in the total number of intermediates involved.
In tr od u ction
On the other hand, and while the subject of transfor-
mation of a terminal alkyne into its vinylidene isomer
promoted by a metal center has been widely addressed,5
the role that polyhydrides play in this transformation
has been scarcely investigated.6
Olefin metathesis is a very useful method for C-C
bond formation in organic synthesis.1 Among all of the
transition-metal complexes that catalyze this reaction,
the ruthenium-based compounds RuCl2(dCR2)(PR′3)2
represented a breakthrough in the field, due to their
wide functional group and protic media tolerance, as
well as because of their high stability and easy han-
dling.2 While the current methods of preparing such
compounds provide a wide array of R groups in the
carbene ligand,2,3 less attention has been paid to the
possibility of introducing different functionalities on the
ruthenium center.4
We find that the complexes RuHX(H2)L2 (X ) Cl, I)
are a convenient source of a 14-e- ruthenium fragment
“RuHClL2” that by reaction with terminal alkynes lead
to the hydrido/vinylidene complexes RuHX(dCdCHR)-
L2, providing a new synthetic approach to the Ru-based
carbenoids described above and also achieving the goal
of functionalizing the ruthenium center. Similar func-
tionalization can be achieved starting from OsH3XL2 (X
) Cl). It will be shown by isotope labeling and theoreti-
cal studies of the reaction path that the hydride initially
on the metal plays not only the role of a spectator ligand
but is an active participant in the formation of the
vinylidene group. Moreover, this theoretical study
† Indiana University. E-mail: caulton@indiana.edu.
‡ Universite´ de Montpellier 2. E-mail: eisenst@sd.univ-montp2.fr.
(1) (a) Ivin, J . K.; Mol, J . C. Olefin Metathesis and Metathesis
Polymerization; Academic Press: London, 1997. (b) Schuster, M.;
Blechert, S. Angew. Chem., Int. Ed. Engl. 1997, 36, 2037.
(2) Nguyen, S. T.; J ohnson, I. K.; Grubbs, R. H. J . Am. Chem. Soc.
1992, 114, 3974.
(3) (a) Wu, Z.; Nguyen, S. T.; Grubbs, R. H.; Ziller, J . W. J . Am.
Chem. Soc. 1995, 117, 5503. (b) Schwab, P.; France, M. B.; Ziller, J .
W.; Grubbs, R. H. Angew. Chem., Int. Ed. Engl. 1995, 34, 2039. (c)
Schwab, P.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem. Soc. 1996, 118,
100. (d) Wilhelm, T. E.; Belderrain, T. R.; Brown, S. N.; Grubbs, R. H.
Organometallics 1997, 16, 3867. (e) Belderrain, T. R.; Grubbs, R. H.
Organometallics 1997, 16, 4001. (f) Oliva´n, M.; Caulton, K. G. J . Chem.
Soc., Chem. Commun. 1997, 1733. (g) Wakatsuki, Y.; Yamazaki, H.;
Kumegawa, N.; Satoh, T.; Satoh, J . Y. J . Am. Chem. Soc. 1991, 113,
9604. (h) Gru¨nwald, C.; Gevert, O.; Wolf, J .; Gonza´lez-Herrero, P.;
Werner, H. Organometallics 1996, 15, 1960.
(5) (a) Bruce, M. I. Chem. Rev. 1991, 91, 197. (b) Esteruelas, M. A.;
Oro, L. A.; Valero, C. Organometallics 1995, 14, 3596. (c) Touchard,
D.; Haquette, P.; Guesmi, S.; Le Pichon, L.; Daridor, A.; Toupet, L.;
Dixneuf, P. H. Organometallics 1997, 16, 3640. (d) Le Lagadec, R.;
Roman, E.; Toupet, L.; Mu¨ller, U.; Dixneuf, P. H. Organometallics
1994, 13, 5030. (e) de los Rios, I.; J ime´nez-Tenorio, M.; Puerta, M. C.;
Valerga, P. J . Am. Chem. Soc. 1997, 119, 6529. (f) Bianchini, C.;
Peruzzini, M.; Vacca, A.; Zanobini, F. Organometallics 1991, 10, 3697.
(g) Barbaro, P.; Bianchini, C.; Peruzzini, M.; Polo, A.; Zanobini, F.;
Frediani, P. Inorg. Chim. Acta 1994, 220, 5. (h) Antonova, A. B.;
Ioganson, A. A. Usp. Khim. 1989, 68, 1197.
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S0276-7333(97)01109-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 06/18/1998

3092 Organometallics, Vol. 17, No. 14, 1998
Oliva´n et al.
Sp ect r oscop ic Ch a r a ct er iza t ion of R u H 6(P t Bu 2Me)2.
In an NMR tube RuH2Cl2(PtBu2Me)2 (10 mg, 0.020 mmol) and
NaBH4 (7.6 mg, 0.20 mmol) were suspended in benzene-d6.
To that suspension, 5 µL of methanol was added. The NMR
tube was kept open until the gas evolution ceased, then the
tube was closed and its NMR spectrum was taken. During
this time, the color changed from red-burgundy to yellowish.
1H NMR (300 MHz, C6D6, 20 °C): -7.45 (br t, J P-H ) 8.1 Hz,
6H, RuH6), 1.20 (vt, N ) 6.1 Hz, 36H, PC(CH3)3), 1.31 (vt, N
) 2.1 Hz, 6H, PCH3). 31P{1H} NMR (121 MHz, C6D6, 20 °C):
78.9 (s).
reveals fundamental structural differences between the
Ru and Os intermediates in this reaction.
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, 13C{1H}, and 31P NMR spectra
were obtained on a Varian Gemini 300, while 2H NMR spectra
were recorded on a Varian Inova 400 instrument. T1 mea-
surements were made at 300 MHz using the inversion-
recovery method and standard Varian software. Chemical
shifts are referenced to residual solvents peaks (1H, 2H,
Ru HI(H2)(P tBu 2Me)2. To a suspension of RuH2Cl2(PtBu2-
Me)2 (300 mg, 0.61 mmol) and NaBH4 (229 mg, 6.1 mmol) in
toluene (8 mL), several drops of methanol were added. After
the mixture was stirred for 10 min, it was filtered. To the
resulting yellow-greenish solution, CH3I (38 µL, 0.61 mmol)
was added and immediate gas evolution and color change (to
brown) was observed. After the mixture was stirred for 1 h,
the volatiles were removed under vacuum, obtaining a brown
solid. Yield: 230 mg (68%). Anal. Calcd for C18H45IP2Ru: C,
39.20; H, 8.22. Found: C, 39.37; H, 7.74. 1H NMR (300 MHz,
C6D6, 20 °C): -16.01 (br s, 3H, Ru-H), 1.04 (vt, N ) 6.1 Hz,
36H, PC(CH3)3), 1.73 (vt, N ) 2.4 Hz, 6H, PCH3). 1H NMR
(300 MHz, C7D8, -90 °C): -15.90 (br s, T1 ) 41 ms, Ru-H).
1H NMR (300 MHz, C7D8, -70 °C): -15.90 (t, J P-H ) 13.8 Hz,
Ru-H). 31P{1H} NMR (121 MHz, C6D6, 20 °C): 59.1 (s). IR
(Nujol, cm-1): ν(Ru-H) 2112 (m), 2062 (m), 1905 (m).
Ru HCl(dCdCHP h )(P tBu 2Me)2. To a solution of RuHCl-
(H2)(PtBu2Me)2 (32 mg, 0.069 mmol) in 0.5 mL of benzene-d6
was added PhCCH (15.5 µL, 0.14 mmol). Immediately, the
color of the solution changed from brown-yellowish to brown.
The reaction was quantitative by NMR, but the complex could
not be isolated as a solid due to its high solubility in all
common organic solvents (it could only be isolated as an oil,
and this prevented carrying out its elemental analysis). 1H
and 13C{1H} NMR spectra show the presence of styrene
together with RuHCl(dCdCHPh)(PtBu2Me)2. 1H NMR (300
MHz, C6D6, 20 °C): -12.65 (t, J P-H ) 17.8 Hz, 1H, Ru-H),
1.20 (vt, N ) 6.2 Hz, 18H, PC(CH3)3), 1.24 (vt, N ) 2.7 Hz,
6H, PCH3), 1.33 (vt, N ) 6.4 Hz, 18H, PC(CH3)3), 4.41 (t, J P-H
) 3.4 Hz, 1H, CHPh), 6.88-7.24 (m, 5H, Ph). 13C{1H} NMR
(75.4 MHz, C6D6, 20 °C): 9.06 (vt, N ) 12.2 Hz, PCH3), 29.53
(vt, N ) 2.4 Hz, PC(CH3)3), 29.89 (vt, N ) 2.6 Hz, PC(CH3)3),
34.47 (vt, N ) 8.2 Hz, PC(CH3)3), 35.76 (vt, N ) 7.5 Hz,
PC(CH3)3), 109.04 (t, J P-C ) 4.0 Hz, RudCdC), 123.12 (s, Ph),
7
13C{1H}) or external H3PO4 (31P). Complexes [RuCl2(COD)]n
and OsH3Cl(PiPr3)2 were synthesized according to published
8
procedures. HCCPh (Aldrich) and HCCSiMe3 (Oakwood) were
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 at
the Chemistry Department, Indiana University.
Ru H2Cl2(P tBu 2Me)2. To a suspension of [RuCl2(COD)]n
(750 mg, 2.68 mmol for n ) 1) in 2-propanol (20 mL), placed
in a Fisher-Porter bottle, was added PtBu2Me (1072 µL, 5.35
mmol). The brown suspension was degassed, and the Fisher-
Porter bottle was filled with H2 (2.5 atm) and heated at 85 °C
for 4 h. The bottle was then recharged to 2.5 atm of H2 and
stirred at 85 °C for 20 h. After this time, the resulting reddish
suspension was transferred to a Schlenk flask and concen-
trated to ca. 5 mL under reduced pressure. The burgundy solid
was filtered, washed with cold diethyl ether, and dried in
vacuo. Yield: 980 mg (74%). Anal. Calcd for C18H44Cl2P2-
Ru: C, 43.72; H, 8.97. Found: C, 43.57; H, 8.28. 1H NMR
(300 MHz, CD2Cl2, 20 °C): -11.31 (t, J P-H ) 29.8 Hz, 2H, Ru-
H), 1.12 (d, J P-H ) 10.2 Hz, 6H, PCH3), 1.51 (d, J P-H ) 14.4
Hz, 36H, PC(CH3)3). 31P{1H} NMR (121 MHz, CD2Cl2, 20
°C): 99.8 (s). IR (Nujol, cm-1): ν(Ru-H) 2162 (s).
Ru HCl(H2)(P tBu 2Me)2. To a suspension of RuH2Cl2(PtBu2-
Me)2 (100 mg, 0.2 mmol) in toluene (10 mL) was added Et3N
(57 µL, 0.4 mmol). After freeze/pump/thaw degassing 3 times,
the suspension was warmed to room temperature and H2 (1
atm) was admitted to the Schlenk flask. In 2 h the reaction
mixture changed to a brown-yellowish solution with a whitish
precipitate. After the solution was stirred for an additional
hour, the toluene solution was filtered through Celite. Re-
moval of the volatiles in vacuo left a brown solid. Yield: 67
mg (72%). Anal. Calcd for C18H45ClP2Ru: C, 47.00; H, 9.86.
Found: C, 46.51; H, 9.40. 1H NMR (300 MHz, C6D6, 20 °C):
-15.78 (br s, 3H, Ru-H), 1.10 (vt, N ) 6.1 Hz, 36H, PC(CH3)3),
1.32 (vt, N ) 2.2 Hz, 6H, PCH3). 31P{1H} NMR (121 MHz,
C6D6, 20 °C): 58.7 (s). IR (Nujol, cm-1): ν(Ru-H) 2125 (m),
2083 (m), 1910 (w).
Ru H2I2(P tBu 2Me)2. A CH2Cl2 (10 mL) solution of RuH2-
Cl2(PtBu2Me)2 (100 mg, 0.2 mmol) was placed in a Schlenk
flask fitted with a rubber septum. To this solution, Me3SiI
(63 µL, 0.44 mmol) was added via syringe at room temperature.
Immediately, the dark red solution color changed to deep
violet. After 10 min of stirring, the volatiles were removed in
vacuo, quantitatively yielding RuH2I2(PtBu2Me)2. Anal. Calcd
for C18H44I2P2Ru: C, 32.92; H, 6.55. Found: C, 33.36; H, 7.02.
1H NMR (300 MHz, CD2Cl2, 20 °C): -8.54 (t, J P-H ) 26.8 Hz,
2H, Ru-H), 1.16 (d, J P-H ) 10.2 Hz, 6H, PCH3), 1.51 (d, J P-H
) 15 Hz, 36H, PC(CH3)3). 31P{1H} NMR (121 MHz, CD2Cl2,
20 °C): 90.4 (s). IR (Nujol, cm-1): ν(Ru-H) 2145 (s).
123.69 (s, Ph), 128.68 (s, Ph), 133.76 (t, J P-C ) 2.4 Hz, Cipso
,
Ph), 331.86 (t, J P-C ) 14.9 Hz, RudC). 31P{1H} NMR (121.421
MHz, C6D6, 20 °C): 42.7 (s). IR (C6D6, cm-1): ν(Ru-H) 2044
(vw), ν(CdC, phenyl) 1587 (s), ν(CdC) 1568 (s).
Ru HCl(dCdCHSiMe3)(P tBu 2Me)2. This compound was
prepared analogously to the method described for RuHCl(d
CdCHPh)(PtBu2Me)2, starting from RuHCl(H2)(PtBu2Me)2 (30
mg, 0.065 mmol) and Me3SiCCH (18.5 µL, 0.13 mmol). 1H and
13C{1H} NMR spectra of the resulting red solution show the
presence of Me3SiCHdCH2 together with RuHCl(dCdCH-
SiMe3)(PtBu2Me)2. 1H NMR (300 MHz, C6D6, 20 °C): -14.95
(dt, J P-H ) 18.3 Hz, J H-H ) 1.8 Hz, 1H, Ru-H), 0.18 (s, 9H,
SiMe3), 1.25 (vt, N ) 6.4 Hz, 18H, PC(CH3)3), 1.35 (vt, N )
2.7 Hz, 6H, PCH3), 1.42 (vt, N ) 6.4 Hz, 18H, PC(CH3)3), 2.59
(dt, J P-H ) 3.6 Hz, J H-H ) 1.8 Hz, 1H, CHSiMe3). 13C{1H}
NMR (75.4 MHz, C6D6, 20 °C): 0.18 (s, SiMe3), 8.51 (vt, N )
12.0 Hz, PCH3), 29.62 (vt, N ) 2.7 Hz, PC(CH3)3), 29.88 (vt, N
) 2.7 Hz, PC(CH3)3), 34.41 (vt, N ) 8.3 Hz, PC(CH3)3), 36.19
(vt, N ) 7.3 Hz, PC(CH3)3), 88.97 (t, J P-C ) 2.7 Hz, RudCd
C), 318.53 (t, J P-C ) 14.7 Hz, RudC). 31P{1H} NMR (121 MHz,
C6D6, 20 °C): 40.3 (s). IR (C6H6, cm-1): ν(Ru-H) 2035 (vw),
ν(CdC) 1595 (s).
Ru HI(dCdCHP h )(P tBu 2Me)2. To a solution of RuHI-
(H2)(PtBu2Me)2 (100 mg, 0.18 mmol) in toluene (5 mL) was
added PhCCH (40 µL, 0.36 mmol). Immediately, the brown-
yellowish solution color changed to dark-brown. The volatiles
(7) Albers, M. O.; Singleton, E.; Yates, J . E. Inorg. Synth. 1989, 26,
253.
(8) Kuhlman, R. H.; Clot, E.; Leforestier, C.; Streib, W. E.; Eisen-
stein, O.; Caulton, K. G. J . Am. Chem. Soc. 1997, 119, 10153.

Formation of Hydrido Vinylidene
Organometallics, Vol. 17, No. 14, 1998 3093
were removed under vacuum, and the residue was dissolved
in 2 mL of pentane and cooled to -78 °C, yielding a brown
solid. Yield: 35 mg (29%). The reaction was quantitative by
NMR and showed the presence of styrene in a similar amount
to that of RuHI(dCdCHPh)(PtBu2Me)2. 1H NMR (300 MHz,
C6D6, 20 °C): -9.80 (t, J P-H ) 18.3 Hz, 1H, Ru-H), 1.19 (vt, N
) 4.5 Hz, 18H, PC(CH3)3), 1.35 (vt, N ) 5.1 Hz, 18H,
20 °C): -0.06 (s, 9H, SiMe3), 1.28 (vt, N ) 6.3 Hz, 36H, PC-
(CH3)3), 1.33 (vt, N ) 3 Hz, 6H, PCH3), 3.57 (s, 3H, MeNC),
3.59 (t, J P-H ) 1 Hz, 6H, MeNC), 6.11 (dt, J H-H ) 21 Hz, J P-H
) 2.1 Hz, Ru-CHdCH), 8.14 (dt, J H-H ) 21 Hz, J P-H ) 1.6
Hz, Ru-CHdCH). 31P{1H} NMR (121 MHz, CDCl3, 20 °C):
43.7 (s). IR (CDCl3, cm-1): ν(NC) 2148 (vs).
Rea ction of OsHCl(dCdCHSiMe3)(P iP r 3)2 w ith CO. A
solution of OsHCl(dCdCHSiMe3)(PiPr3)2 (10 mg, 0.015 mmol)
in benzene-d6 (0.5 mL) was placed in an NMR tube with a
Teflon closure. The solution was frozen in liquid N2, and the
headspace of the tube was evacuated and filled with CO (1
atm). Upon warming, an immediate color change from red to
very pale yellow was observed. 1H and 31P NMR spectroscopies
show clean conversion to Os{(E)-CHdCHSiMe3}Cl(CO)2(PiPr3)2.
1H NMR (300 MHz, C6D6, 20 °C): 0.21 (s, 9H, SiMe3), 1.09
(dvt, J P-H ) 6.6 Hz, N ) 12.9 Hz, 18H, PCH(CH3)2), 1.29 (dvt,
J P-H ) 6.6 Hz, N ) 13.8 Hz, 18H, PCH(CH3)2), 2.85 (m, 6H,
PCH(CH3)2), 6.98 (dt, J H-H ) 21.3 Hz, J P-H ) 2.2 Hz, 1H, Os-
CHdCH), 8.98 (d, J H-H ) 21.3 Hz, 1H, Os-CHdCH). 31P-
{1H} NMR (121 MHz, C6D6, 20 °C): 4.6 (s). IR (C6D6, cm-1):
1996, 1923 ν(CO).
Rea ction of OsHCl(dCdCHSiMe3)(P iP r 3)2 w ith CNMe.
To a solution of OsHCl(dCdCHSiMe3)(PiPr3)2 (10 mg, 0.015
mmol) in benzene-d6 (0.5 mL) placed in an NMR tube, MeNC
(1.7 µL, 0.031 mmol) was added via syringe, and an immediate
color change from red to pale yellow was observed. 1H and
31P{1H} NMR spectroscopies show quantitative conversion to
Os{(E)-CHdCHSiMe3}Cl(CNMe)2(PiPr3)2. 1H NMR (300 MHz,
C6D6, 20 °C): 0.35 (s, 9H, SiMe3), 1.32 (dvt, J H-H ) 6.9 Hz, N
) 12.3 Hz, 18H, PCH(CH3)2), 1.39 (dvt, J H-H ) 6.6 Hz, N )
12.9 Hz, 18H, PCH(CH3)2), 2.53 (s, 3H, MeNC), 2.81 (s, 3H,
MeNC), 2.84 (m, 6H, PCH(CH3)2), 6.78 (dt, J H-H ) 21.3 Hz,
J P-H ) 2.7 Hz, 1H, Os-CHdCH), 9.74 (d, J H-H ) 21.3 Hz,
1H, Os-CHdCH). 31P{1H} NMR (121 MHz, C6D6, 20 °C): -1.4
(s).
PC(CH3)3), 1.44 (vt, N ) 1.8 Hz, 6H, PCH3), 4.40 (t, J P-H
)
2.8 Hz, 1H, CHPh), 6.85-7.23 (m, 5H, Ph). 13C{1H} NMR
(100.6 MHz, C6D6, 20 °C): 12.28 (vt, N ) 12.2 Hz, PCH3), 30.05
(vt, N ) 2.7 Hz, PC(CH3)3), 30.34 (vt, N ) 2.7 Hz, PC(CH3)3),
34.76 (vt, N ) 7.9 Hz, PC(CH3)3), 36.65 (vt, N ) 8.0 Hz, PC-
(CH3)3), 108.68 (t, J P-C ) 4.1 Hz, RudCdC), 123.66 (s, Ph),
124.00 (s, Ph), 128.60 (s, Ph), 132.71 (t, J P-C ) 2.7 Hz, Cipso
,
Ph), 328.43 (t, J P-C ) 14.2 Hz, RudC). 31P{1H} NMR (121
MHz, C6D6, 20 °C): 46.2 (s). IR (Nujol, cm-1): ν(Ru-H) 1923
(w), ν(CdC) 1612 (s), ν(CdC, phenyl) 1591 (s).
Ru HI(dCdCHSiMe3)(P tBu 2Me)2. To a solution of RuHI-
(H2)(PtBu2Me)2 (100 mg, 0.18 mmol) in toluene (5 mL), Me3-
SiCCH (51 µL, 0.36 mmol) was added. Immediately, the
brown-yellowish solution color changed to dark red. The
volatiles were removed under vacuum, and the residue was
dissolved in 2 mL of pentane and cooled to -78 °C, yielding
an orange solid. Yield: 38 mg (32%). The reaction was
quantitative by NMR spectroscopies and showed the presence
of Me3SiCHdCH2 in a similar amount to that of RuHI-
(dCdCHSiMe3)(PtBu2Me)2. Anal. Calcd for C23H53IP2RuSi:
C, 42.65; H, 8.25. Found: C, 42.89; H, 7.70. 1H NMR (300
MHz, C6D6, 20 °C): -11.14 (t, J P-H ) 19.2 Hz, 1H, Ru-H),
0.15 (s, 9H, SiMe3), 1.21 (vt, N ) 6.4 Hz, 18H, PC(CH3)3), 1.40
(vt, N ) 6.4 Hz, 18H, PC(CH3)3), 1.51 (vt, N ) 2.4 Hz, 6H,
PCH3), 2.55 (t, J P-H ) 3.3 Hz, 1H, CHSiMe3). 13C{1H} NMR
(75.429 MHz, C6D6, 20 °C): 0.38 (s, SiMe3), 11.08 (vt, N ) 11.6
Hz, PCH3), 29.65 (vt, N ) 4.1 Hz, PC(CH3)3), 29.82 (vt, N )
2.7 Hz, PC(CH3)3), 34.26 (vt, N ) 8.2 Hz, PC(CH3)3), 36.75 (vt,
N ) 7.5 Hz, PC(CH3)3), 88.69 (t, J P-C ) 2.7 Hz, RudCdC),
314.80 (t, J P-C ) 13.7 Hz, RudC). 31P{1H} NMR (121.421
MHz, C6D6, 20 °C): 44.1 (s). IR (Nujol, cm-1): ν(Ru-H) 2019
(m), ν(CdC) 1593 (s).
Com p u ta tion a l Deta ils. Ab initio calculations were car-
ried out with the Gaussian 94 set of programs9a within the
framework of DFT at the B3LYP level.9b LANL2DZ effective
core potentials (quasi-relativistic for the metal centers) were
used to replace the 28 innermost electrons of Ru, the 60
innermost electrons of Os, as well as the 10 core electrons of
P and Cl.9c The associated double ú basis set9c augmented by
a d function was used for Cl and P.10 The other atoms were
represented by a 6-31G(d,p) basis set.11 The H atoms of PH3
were represented at the STO-3G level.12 Full geometry
optimization was performed with no symmetry restriction, and
the nature of the optimized structure as a minimum or
transition state was assigned by numerical frequency calcula-
tions. Differences in enthalpies were evaluated from the
frequency calculations. The transition-state structures were
given small structural perturbations, then further geometri-
cally optimized to ensure that they connect the reactant and
product of interest. Since, with one exception, the enthalpy
differences are, in general, close to the electronic energy
difference (discrepancy of less than 1 kcal mol-1), mention of
enthalpy differences will be given only when needed.
OsHCl(dCdCSiMe3)(P iP r 3)2. This compound was pre-
pared analogously to the method described for RuHI(dCd
CHSiMe3)(PtBu2Me)2, starting from OsH3Cl(PiPr3)2 (30 mg,
0.054 mmol) and Me3SiCCH (15.5 µL, 0.109 mmol). 1H NMR
(300 MHz, C6D6, 20 °C): -19.37 (t, J P-H ) 13.9 Hz, 1H, Os-
H), -0.09 (t, J P-H ) 2.5 Hz, 1H, CHSiMe3), 0.16 (s, 9H, SiMe3),
1.27 (dvt, J H-H ) 7.5 Hz, N ) 14.4 Hz, 36H, PCH(CH3)2), 2.80
(m, 6H, PCH(CH3)2). 13C{1H} NMR (75.429 MHz, C6D6, 20
°C): 1.31 (s, SiMe3), 20.14 (s, PCH(CH3)2), 20.31 (s, PCH-
(CH3)2), 25.30 (vt, N ) 12.1 Hz, PCH(CH3)2), 86.36 (t, J P-C
)
2.5 Hz, OsdCdC), 275.00 (t, J P-C ) 9.0 Hz, OsdCdC). 31P-
{1H} NMR (121.421 MHz, C6D6, 20 °C): 36.9 (s). IR (C6H6,
cm-1): ν(Os-H) 2040 (vw), ν(CdC) 1591 (s).
Ru DI(dCdCHP h )(P tBu 2Me)2. To a solution of RuHI(H2)-
(PtBu2Me)2 (10 mg, 0.018 mmol) in 0.5 mL of benzene was
added PhCCD (4 µL, 0.36 mmol). Immediately, the brown-
yellowish solution color changed to to dark-brown. 2H NMR
(61.421 MHz, C6H6, 20 °C): -9.72 (s, Ru-D), 5.6 (s, cis-PhCHd
CHD).
Ru DCl(dCdCHP h )(P tBu 2Me)2. This compound was pre-
pared similarly to the method described for RuDI(dCdCHPh)-
(PtBu2Me)2, starting from RuHCl(H2)(PtBu2Me)2 (10 mg, 0.022
mmol) and PhCCD (4.8 µL, 0.044 mmol). 2H NMR (61.421
MHz, C6H6, 20 °C): -12.53 (s, Ru-D).
(9) (a) 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-Alham, M. A.; Zakrzew-
ski, V. G.; Ortiz, J . V.; Foresman, J . B.; Peng, C. Y.; Ayala, P. Y.; Chen,
W.; Wong, M. W.; Andres, J . L.; Reploge, 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
B3; Gaussian, Inc.: Pittsburgh, PA, 1995. (b) Becke, A. D. J . Chem.
Phys. 1993, 98, 5648. (c) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985,
82, 284 and 299.
(10) Ho¨llwarth, A.; Bo¨hme, M.; Dapprich, S.; Ehlers, A. W.; Gobbi,
A.; J onas, V; Ko¨hler, K.; Stegmann, R.; Veldkamp, A.; Frenking, G.
Chem. Phys. Lett. 1993, 208, 237.
(11) Hariharan, P. C.; Pople, J . Theor. Chim. Acta 1973, 28, 213.
(12) Hehre, W. J .; Stewart, R. F.; Pople, J . A. J . Chem. Phys. 1969,
51, 2657.
[Ru {(E)-CHdCHSiMe3}(CNMe)3(P tBu 2Me)2]I. To a so-
lution of RuHI(dCdCHSiMe3)(PtBu2Me)2 (50 mg, 0.077 mmol)
in toluene (5 mL) was added MeNC (17 µL, 0.31 mmol).
Immediately, the color of the solution changed from red to
colorless. After 30 min, the solvent was removed and pentane
was added to give a pale yellow solid. Yield: 32 mg (53%).
Anal. Calcd for C29H62IN3P2RuSi: C, 45.18; H, 7.98; N, 5.45.
Found: C, 44.77; H, 7.6; N, 5.17. 1H NMR (300 MHz, CDCl3,

3094 Organometallics, Vol. 17, No. 14, 1998
Oliva´n et al.
Resu lts
Syn th esis of Com p lexes Ru HX(H2)(P tBu 2Me)2.
The recent synthesis of the compound RuH2Cl2L2 (L )
PiPr3) in Werner’s group3h has opened the door to an
easy and very convenient route for the synthesis of the
known compounds RuHX(H2)L2 that otherwise had to
be prepared by using Chaudret’s procedure,13 which is
less convenient, mainly for the irksome synthesis and
low yields of the starting material, Ru(COD)(COT).
Hydrogenolysis (<1.5 atm of H2) of RuH2Cl2L2 (L )
PtBu2Me) (eq 1) in the presence of stoichiometric base
leads (within 2 h at room temperature) to RuHCl-
(H2)(PtBu2Me)2 in 72% isolated yield.
triplets, indicating diastereotopic inequivalence. Since
the molecules of the type MHX(CO)L2 (L ) tertiary
phosphine) adopt a square-based pyramid geometry
with the hydride occupying the axial position and the
π-donor and π-acceptor ligands occupying trans basal
positions,16 one might propose that the compounds
RuHX(dCdCHR)L2, which also carry a π-donor (X-)
and π-acceptor ligand (vinylidene), adopt a similar
geometry. However, a closer look at their 1H NMR
spectra reveals the weakness of this proposal: (i) if the
hydride in the compounds RuHX(dCdCHR)L2 is in the
apical position (i.e., trans to the empty site), we will
RuH2Cl2L2 + NEt3 + H2 f
RuHCl(H2)L2 + [HNEt3]Cl (1)
A similar method for preparing RuHCl(H2)(PCy3)2 has
been reported very recently.3d However, this procedure
(analogous to eq 1) fails with RuH2I2L2 (L ) PtBu2Me),
where after 113 h of reaction, only 50% conversion was
achieved. This could be understood in light of the
thermodynamic parameters obtained for the analogous
OsH2X2(PiPr3)2 system, where the heavier halide favors
H2 coordination enthalpically but disfavors it entropi-
cally.14 Alternatively, RuHI(H2)L2 was prepared by
treatment of a solution of RuH6L2 with CH3I in about
60% yield.
1
expect its H NMR chemical shift to be similar to those
reported for RuHX(CO)L2 (around -24 ppm).16a Con-
trary to this expectation, there is a difference of more
than 10 ppm. (ii) In the series of compounds RuHX-
(CO)L2, the difference in hydride chemical shifts be-
tween the chloride and iodide derivatives is only 0.8
ppm, while in the complexes RuHX(dCdCHR)L2 it is
2.8 ppm when R ) Ph and 3.8 ppm when R ) SiMe3,
indicating a greater influence of the halide on the
hydride chemical shift. These observations are easily
explained in light of the results of an ab initio (B3LYP)
calculation study on the model molecule RuHCl(dCd
CH2)(PH3)2 (Figure 1, structure 5Ru ) whose geometry
has been discussed previously.17 Briefly, the H-Ru-
Cl angle, 129.6°, is large enough that the hydride
chemical shift should be significantly influenced by
halide identity.
RuH6L2 (L ) PtBu2Me) was prepared in situ by
1
reaction of RuH2Cl2L2 with excess of NaBH4. The H
NMR spectrum shows a triplet at -7.45 ppm, with a
J P-H coupling constant of 8.1 Hz. This chemical shift
agrees very well with the ones for related RuH6L2 (L )
PCy3, PiPr3) reported previously in the literature.13,15
This compound, analogously to the one with PiPr3, is
highly unstable under vacuum,13 preventing its isola-
tion.
Similar to the ruthenium complexes, the osmium
trihydride OsH3Cl(PiPr3)2 reacts with Me3SiCCH to give
OsHCl(dCdCHSiMe3)(PiPr3)2 and (Me3Si)HCdCH2 in
the time of mixing in benzene.
The RuHX(H2)(PtBu2Me)2 complexes show one upfield
t
resonance due to all three H atoms on Ru and one Bu
1
virtual triplet by H NMR at 25 °C in benzene-d6. The
T1 value of the hydride signal in the iodide derivative
(41 ms at 300 MHz and the lowest available tempera-
ture, -90 °C) is short enough to be consistent with a
RuH(H2) structure.
Mech a n istic Stu d ies. Attempts to search for inter-
mediates of the reaction at low temperature failed.
When the reactants were combined at -78 °C in an
NMR tube and then the tube inserted in a precooled
NMR probe (-80 °C), no intermediate could be detected,
observing only starting material and the final vinylidene
on warming. As an alternative method, we decided to
perform a labeling experiment: the reactions of RuHX-
(H2)(PtBu2Me)2 (X ) Cl, I) with phenylacetylene-d1,
Syn th esis a n d Str u ctu r e of Com p lexes Ru HX(d
CdCHR)(P tBu 2Me)2. Reaction of RuHX(H2)L2 (L )
PtBu2Me; X ) Cl, I) with terminal alkynes in a 1:2 molar
ratio affords (time of mixing in benzene) the unsatur-
ated hydrido/vinylidene compounds RuHX(dCdCHR)-
L2 (R ) Ph, SiMe3) and the corresponding alkene as the
only organic product (eq 2). The most characteristic
features in the 13C{1H} NMR spectra are the low-field
triplets at about 320 (J P-C ) 14 Hz) and 99 ppm (J P-C
) 3.5 Hz), which by comparison are assigned to CR and
1
PhCCD, were carried out. The H NMR spectra of the
resulting products show no resonance assignable to Ru-
H. The presence of deuterium attached to the Ru center
2
was confirmed by H NMR spectroscopy, which shows
singlets at -9.72 (X ) I) and -12.53 ppm (X ) Cl). In
general, formation of a vinylidene ligand from a termi-
nal alkyne has been speculated to start with η2-
coordination of the alkyne to the metal center, followed
by (i) hydride migration to the â-carbon (1,2-hydrogen
1
Câ vinylidene carbon atoms. The PMe H NMR signal
appears as a triplet, consistent with transoid phos-
1
phines, while the tBu H NMR signals show two virtual
(13) Burrow, T.; Sabo-Etienne, S.; Chaudret, B. Inorg. Chem. 1995,
34, 2470.
(14) Kuhlman, R. H.; Gusev, D. G.; Eremenko, I. L.; Berke, H.;
Huffman, J . C.; Caulton, K. G. J . Organomet. Chem. 1997, 536-537,
139.
(15) (a) Chaudret, B.; Poilblanc, R. Organometallics 1985, 4, 1722.
(b) Arliguie, T.; Chaudret, B.; Morris, R. H.; Sella, A. Inorg. Chem.
1988, 27, 598.
(16) (a) Poulton, J . T.; Sigalas, M. P.; Folting, K.; Streib, W. E.;
Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1994, 33, 1476. (b) Gill,
D. F.; Shaw, B. L. Inorg. Chim. Acta 1979, 32, 99. (c) Esteruelas, M.
A.; Werner, H. J . Organomet. Chem. 1986, 303, 221.
(17) Oliva´n, M.; Eisenstein, O.; Caulton, K. G. Organometallics 1997,
16, 2227.

Formation of Hydrido Vinylidene
Organometallics, Vol. 17, No. 14, 1998 3095
shift mechanism. On the other hand, the 1,3-hydrogen
shift is ruled out because the oxidative addition of the
alkyne would give a Ru(IV) alkynyl-dihydride inter-
mediate, which would thus lead to a mixture of RuDX-
(dCdCHPh)L2 and RuHX(dCdCDPh)L2. This dis-
agrees with our experimental observation.
The isotopic labeling is consistent with a path which
starts with the insertion of an alkyne into the Ru-H
bond, to make a vinyl complex, followed by the selective
migration of the R-hydrogen of the vinyl to the metal.
In this manner, the hydrogen that was originally bonded
to the ruthenium ends up at the â-carbon atom of the
vinylidene in a selective fashion.
In the 1:2 reaction of MH3ClL2 (M ) Ru and Os) with
terminal alkynes, the function of the first alkyne is to
abstract two H atoms from M. This reaction occurs with
the usual syn addition of two H’s to the triple bond, and
the mechanistic focus of our computational study of the
reaction mechanism, therefore, became the second stage
of the reaction: combination of acetylene with the
fragment MHCl(PH3)2. How does it form the vinylidene
complex MHCl(CCH2)(PH3)2? We have answered this
question by a full study of the reaction path from
reactants to products. This path raises several ques-
tions. One starts with 14-e- RuHClL2 and a ligand that
probably coordinates to the metal prior to insertion to
make a 16-e- complex. What is the driving force to form
a vinyl ligand which is again a 14-e- species? The next
step involves an R-hydrogen migration (from C to Ru)
transforming vinyl to hydrido vinylidene. This migra-
tion has been observed in a number of cases.18,19 To
better understand this pathway, we have used ab initio
(B3LYP) calculations and the model systems MHCl-
(PH3)2 (M ) Ru, Os) and C2H2.
Th eor etica l Stu d y
The geometries of all structures that have been
optimized as minima or transition states are collected
in Figure 1, and the energy scheme for the reaction
paths is shown in Figure 2 for Ru. The corresponding
results for Os are shown in Figures 3 (geometries) and
4 (energy diagram).
(A) Rea ction P a th for Ru . The four-coordinate
model complex RuHCl(PH3)2, 1Ru , is not planar but has
a saw-horse geometry with trans phosphines and H-Ru-
Cl ) 101.3° (Figure 1). This angle, marginally larger
+
than H-Ir-H in IrH2(PH3)2 (88.9°),20 H-Ru-C in
RuH(CO)(PH3)2+ (87.0°),21 and C-Ru-C in Ru(Ph)(CO)-
(PH3)2 (97.4°),22 illustrates that a d6 tetracoordinated
+
complex prefers to be a fragment of an octahedron with
(18) Bell, T. W.; Haddleton, D. M.; McCamley, A.; Partridge, M. G.;
Perutz, R. N.; Willner, H. J . Am. Chem. Soc. 1990, 112, 9212.
(19) (a) Gibson, V. C.; Parkin, G.; Bercaw, J . E. Organometallics
1991, 10, 220. (b) van Asselt, A.; Burger, B. J .; Gibson, V. C.; Bercaw,
J . E. J . Am. Chem. Soc. 1986, 108, 5347. (c) Beckhaus, R.; Thiele, K.-
H.; Stro¨hl, D. J . Organomet. Chem. 1989, 369, 43. (d) Dziallas, M.;
Werner, H. J . Organomet. Chem. 1987, 333, C29. (e) Alvarado, Y.;
Boutry, O.; Gutie´rrez, E.; Monge, A.; Nicasio, M. C.; Poveda, M. L.;
Pe´rez, P. J .; Ru´ız, C.; Bianchini, C.; Carmona, E. Chem. Eur. J . 1997,
3, 860. (f) Beckhaus, R. J . Chem. Soc., Dalton Trans. 1997, 1991. (g)
Beckhaus, R. Angew. Chem., Int. Ed. Engl. 1997, 36, 686. (h) Luinstra,
G. A.; Teuben, J . H. Organometallics 1992, 11, 1793.
(20) Cooper, A. C.; Streib, W. E.; Eisenstein, O.; Caulton, K. G. J .
Am. Chem. Soc. 1997, 119, 9069.
(21) Huang, D.; Huffman, J . C.; Bollinger, J . C.; Eisenstein, O.;
Caulton, K. G. J . Am. Chem. Soc. 1997, 119, 7398.
(22) Huang, D.; Streib, W. E.; Eisenstein, O.; Caulton, K. G. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2004.
F igu r e 1. Optimized ab initio (B3LYP) structures (Å, deg)
of reactants, intermediates, products, and transition states
for the formation of RuHCl(CdCH2)(PH3)2 from RuHCl-
(PH3)2 and C2H2.
shift) or (ii) insertion of the metal into the H-C bond
to give a hydrido alkynyl that rearranges to the vi-
nylidene (1,3-hydrogen shift).5a In our case, the pres-
ence of H, and not D, on the â-carbon atom of the
vinylidene excludes the possibility of a 1,2-hydrogen

3096 Organometallics, Vol. 17, No. 14, 1998
Oliva´n et al.
F igu r e 2. Energy diagram (kcal mol-1) for the formation of RuHCl(CdCH2)(PH3)2 from RuHCl(PH3)2 and C2H2. (a) In the
lower path, the reaction is initiated by an insertion of the alkyne into the Ru-H(1) bond. Two transition states have been
located for the 3 to 4 transformation (see text). The higher one TS3-4(in v), 21.7 kcal mol-1 above 3, is not shown. (b) In the
upper path, a 1,2-migration occurs within the coordinated alkyne. This path gives 5Ru with the H(1) and H(3) labels reversed.
two empty coordination sites in order to keep the six
electrons of the metal in nonbonding orbitals (t2g-like
occupied d orbitals of an octahedron).
elongation of the C-C bond (1.252 vs 1.205 Å in free
H-CC-H), the alkyne behaves like a two-electron donor
to form a 16-electron complex. The insertion of the
alkyne requires a small activation energy (6.6 kcal mol-1
The presence of two empty coordination sites makes
1Ru a strong Lewis acid and the coordination of the
alkyne exothermic. If the C-C bond serves as an
above 2πRu) and gives a new 14-electron vinyl complex
3Ru , 10.4 kcal mol-1 more stable than 2π
.
The
Ru
Ru
Ru
Ru
structure of the transition state TS2-3 resembles 2π
with a Ru-H(1) bond (1.621 Å) that is still a typical
length and a C-C bond that is hardly elongated (1.275
Å). The hydride H(1) has moved significantly toward
the alkyne, which is now less symmetrically bonded to
Ru (Ru-C(1) ) 2.085 Å; Ru-C(2) ) 2.212 Å). During
this insertion process, the carbon which will remain
bonded to the metal (C(1)) moves very little. Thus, the
insertion reaction is better viewed as H(1) moving
toward C(2) while the Ru-C(1) bond is being estab-
lished. Similar results have been observed in other
insertion reactions.23 The migration of H(1) occurs with
the alkyne and Ru-H(1) bond being coplanar. This step
results in the formation of a vinyl intermediate 3Ru
where the C(1)-H(3) bond of the vinyl group is directed
toward the chloride and not toward the empty metal
site. The saw-horse structure of 3Ru is similar to that
of 1Ru (Cl-Ru-C(1) ) 112°), but the vinyl ligand is not
electron donor, an alkyne complex 2π is formed, while
if the C-H bond serves as an electron donor, a σ C-H
bond complex 2σRu is formed. As expected, the formation
of 2π is more exothermic (32.3 kcal mol-1) than that
Ru
of 2σ (15.2 kcal mol-1). For both complexes, the
Ru
coordination sphere around the metal is square-pyra-
midal with an apical hydride. This geometry minimizes
the trans influence within the complex since the stron-
gest σ-donor ligand (H(1)) is trans to the empty site. It
also maximizes the back-donation from the metal d
orbital destabilized by one Cl lone pair into the empty
orbitals of the alkyne (π*CC or σ*CH). As it will appear
in the following, these two different coordination modes
are initial structures for different mechanisms for
formation of the hydrido vinylidene complex. The
insertion of the alkyne into the Ru-H bond is initiated
Ru
from 2πRu, while the 1,2-migration is initiated from 2σ
(Figure 2). It should be kept in mind that isotopic
labeling is only consistent with the first mechanism.
(i) F or m a tion of th e Hyd r id o/Vin ylid en e via
In ser tion in to th e Ru -H Bon d . In the alkyne
complex 2πRu, the two Ru-C bonds have similar lengths,
indicating a true η2-coordination. From the moderate
(23) See, for instance: Han, Y.; Deng, L.; Ziegler, T. J . Am. Chem.
Soc. 1997, 119, 5939. Deng, L.; Woo, T. K.; Cavallo, L.; Maryl, P. M.;
Ziegler, T. J . Am. Chem. Soc. 1997, 119, 6177. Musaev, D. G.; Froese,
R. D.; Svensson, M.; Morokuma, K. J . Am. Chem. Soc. 1997, 119, 367.
Froese, R. D. J .; Musaev, D. G.; Matsubara, T.; Morokuma, K. J . Am.
Chem. Soc. 1997, 119, 7190.

Formation of Hydrido Vinylidene
Organometallics, Vol. 17, No. 14, 1998 3097
plane while having never undergone a full rotation.
Ru
Ru
Comparing TS3-4 and TS3-4(in v) clearly reveals the
difficulty to reach a planar structure for d6 Ru and the
strong preference for a saw-horse structure. The heavy
twist of the vinyl could certainly be diminished in the
case of bulky phosphines, so that this transition state
may apply for very large phosphine ligands with ap-
proximately the same energy cost as in the PH3 model
system. Structure 4Ru is another 14-electron tetraco-
ordinated vinyl complex which resembles 3Ru but with
a different conformation of the vinyl group. In 4Ru , the
vinyl group is coplanar with Ru-Cl since no short
contacts between Cl and the vinyl group prevent pla-
narity. Any agostic C(1)-H(3) bond in 4Ru is doubtful
since the stretch (1.114 Å) of C(1)-H(3) from its value
(1.094 Å) in 3Ru is not associated with any significant
stabilization (4Ru is more stable than 3Ru by only 0.2
kcal mol-1). The vinyl complex 4Ru has the proper
geometry to undergo an R-hydride migration, which does
indeed occur easily since the associated transition state
Ru
TS4-5 is 3.6 kcal mol-1 (and only 0.4 kcal mol-1 for
the enthalpy difference) above 4Ru
.
To reach this
transition state, the Cl-Ru-C(1) angle has opened
drastically from 116.5° in 4Ru to 148.7° in TS4-5
,
Ru
which brings H(3) to the empty site of the metal. The
C(1)-H(3) bond has stretched considerably (1.519 Å),
while the Ru-H(3) bond is already significantly formed
(1.676 Å); that is, H(3) truly bridges Ru and C(1) in the
transition state. The angle Ru-C(1)-C(2) is essentially
180°, as it is in product 5Ru
.
F igu r e 3. Optimized ab initio (B3LYP) structures (Å, deg)
of reactants, intermediates, products, and transition states
for the formation of OsHCl(CdCH2)(PH3)2 from OsHCl-
(PH3)2 and C2H2.
The hydrido/vinylidene 5Ru is only 3.2 kcal mol-1
below the most stable vinyl intermediate 4Ru
.
The
coordination at the metal is that of a distorted trigonal
bipyramid (Y geometry) with a small C(1)-Ru-H(3)
angle (84.8°), and the vinylidene group lies in the C(1)-
Ru-H(3) plane. This geometry has been extensively
discussed previously.17,24 It is favored by the presence
of a π-donor ligand Cl which forms a Ru-Cl multiple
coplanar with the Ru-Cl bond (Cl-Ru-C(1)-C(2)
dihedral angle ) 12°) to avoid close contacts between
Cl and H(3). The structure of 3Ru is not suited for an
R-hydride migration since the C(1)-H(3) bond is not
directed toward the empty site of the metal. To achieve
that geometry, the whole vinyl group can either rotate
around the Ru-C(1) bond or the metal can invert. The
2
2
bond and a potent back-donation from the occupied dx -y
into the empty p orbital on C(1), which accounts for the
short Ru-C(1) distance (1.819 Å).
Ru
transition state for rotation of the vinyl group TS3-4
(ii) F or m a tion of th e Hyd r id o/Vin ylid en e via 1,2-
Migr a t ion Wit h in t h e Coor d in a t ed Acet ylen e
Liga n d . As mentioned earlier, coordination of the C-H
bond is a less favorable alternative to coordination of
the π system to the empty site of 1Ru . This starting
has been located 3.7 kcal mol-1 above 3Ru . It has the
same saw-horse structure as 3Ru and an essentially
identical geometry except for the conformation of the
vinyl (Cl-Ru-C(1)-C(2) ) 77°). This rotation brings
the closest H of the vinyl within 2.1 Å of the H of PH3.
The calculated value is thus a lower limit to the real
rotational barrier with more bulky phosphines. Since
it is difficult to estimate if the bulk of the phosphine
could prevent the transformation, we searched for
another path that did not involve the full rotation of
the phosphine but instead the inversion at the metal
Ru
geometry 2σ leads to a transition state which describes
the 1,2-migration of the hydrogen from C(1) to C(2). This
Ru
transition state TS2-5
leads to the final hydrido/
Ru
vinylidene in only one step, but the energy of TS2-5
is much higher than any stationary point of the previous
path (26.0 kcal mol-1 above TS2-3Ru ) and is even
marginally higher (0.3 kcal mol-1) than the separated
reactants 1Ru and H-CC-H. It is, thus, much more
unfavorable than the multistep reaction initiated by the
insertion into Ru-H(1). The geometry of the transition
Ru
center. The transition state TS3-4(in v) for this step
was located at a rather high energy (21.7 kcal mol above
3Ru ). In this structure, the vinyl group has continued
its rotation away from the Cl-Ru-C(1) plane (Cl-Ru-
C(1)-C(2) dihedral angle ) 67°). The Cl-Ru-C(1)
angle has drastically increased (172.3°), and the coor-
dination around the metal is almost square planar.
Ru
state TS2-5 is that of a square pyramid with an apical
hydride, an angle Cl-Ru-C(1) equal to 176.8°, and the
migrating H not yet bridging the C(1)-C(2) bond (C(2)-
C(1)-H(1) ) 83.1°).
(iii) F or m a t ion of t h e H yd r id o/Vin ylid en e
th r ou gh a Ru (IV) In ter m ed ia te. The last mecha-
Ru
Analysis of the transition vector at TS3-4(in v) shows
that the 3Ru to 4Ru transformation is an inversion at
the metal center occurring with a very heavily twisted
vinyl group. As soon as C(1) has crossed over the Ru-
Cl axis, the vinyl group falls back into Cl-Ru-C(1)
(24) J ean, Y.; Eisenstein, O. Polyhedron 1988, 7, 405. Rachidi, I.
E.-I.; Eisenstein, O.; J ean, Y. New J . Chem. 1990, 14, 671. Riehl, J .-
F.; J ean, Y.; Eisenstein, O. Pe´lissier, M. Organometallics 1992, 11, 729.

3098 Organometallics, Vol. 17, No. 14, 1998
Oliva´n et al.
F igu r e 4. Energy diagram (kcal mol-1) for the formation of OsHCl(CdCH2)(PH3)2 from OsHCl(PH3)2 and C2H2.
nism which could be suggested for the formation of the
vinyl complex is through a Ru(IV) dihydrido complex
A. It is remarkable that the η1-vinyl species 4Ru is
phosphine substituents can provide additional stabi-
lization,20-22 going through 14-electron complexes should
be even easier.
(B) Th e Os An a logu es. We calculated the path in
the case of Os with the goal of examining the similarities
and differences between the two paths. This was
prompted by our recent findings that Ru and Os can
lead to significant differences in the geometries of
intermediate and transition states.25 The initial reac-
tive metal fragment is considered to be OsHClL2, and
the only alkyne complex that was located on the
potential energy path was 2πOs. The results are pre-
sented in Figures 3 (geometries) and 4 (energy diagram).
The stabilization upon coordination of the alkyne is
considerably more exothermic (46.5 kcal mol-1) than for
Ru, indicating a strong Os-ligand interaction. The
structure of 2πOs is very similar to that of 2πRu. The C-C
preferable to structure A. In fact, no such dihydrido
complex with either trans or cis hydrides has been found
to be a minimum on the potential energy surface.
Calculations of a trans dihydrido complex enforcing C2v
symmetry gives a structure 44.3 kcal mol-1 above the
14-electron vinyl species, excluding that any such Ru-
(IV) species could be on the path to the hydrido/
vinylidene from the acetylene complex.
(iv) Discu ssion of th e P a th s for F or m a tion of 5Ru
.
bond length is almost identical in the structures. The
The preferred path is, thus, the one initiated by inser-
tion of the alkyne into the Ru-H bond, in full agreement
with the isotopic labeling studies. The insertion of the
alkyne into the Ru-H bond is followed by a structural
transformation that leads to a 14-electron intermediate,
which permits the R migration of H to Ru. Two
pathways for this transformation have been found. In
the most energetically facile path, the vinyl rotates
without changing the coordination geometry of the
metal. In a significantly energetically more demanding
path, an inversion occurs at the metal. However, the
associated transition state has an energy well below that
of the reactants, which should make this step feasible.
Formation of successive intermediates is thermody-
namically favored. It is remarkable than the 14-
electron structures are so competitive with respect to
the initial 16-electron coordinated alkyne. In the ex-
perimental species, where agostic interactions from
Os
energy required to reach TS2-3
for insertion into
Os-H is 11.3 kcal mol-1, compared to 6.6 kcal mol-1
for Ru; the geometries of the transition states are
similar. In the case of Os, the two metal-C distances
are more strongly differentiated (Os-C(1) 2.074 Å, Os-
C(2) 2.258 Å; Ru-C(1) 2.085 Å, Ru-C(2) 2.212 Å) while
C(2)-H(1) bond formation is more advanced (1.443 Å
for Os and 1.581 Å for Ru). A major difference between
the two metals is the structure of the intermediate 3Os
.
It is an η2-vinyl complex with the C-C bond coplanar
with Os-Cl. The C-C bond is long (1.411 Å) and the
Os-C(1) bond very short (1.876 Å), while Os-C(2) is
rather long (2.236 Å) but well within the Os-C bonding
(25) (a) Spivak, G. J .; Coalter, J . N.; Oliva´n, M.; Eisenstein, O.;
Caulton, K. G. Organometallics 1998, 17, 999. (b) Huang, D.; Oliva´n,
M.; Huffman, J . C.; Eisenstein, O.; Caulton, K. G. Organometallics,
submitted for publication.

Formation of Hydrido Vinylidene
Organometallics, Vol. 17, No. 14, 1998 3099
interaction. It should be noted that no σ-bonded vinyl
structure could be found on the potential energy surface
for Os, while no η2-vinyl complex was obtained as a
stable minimum for Ru.
4). The reaction path has several interesting features:
while coordination of the alkyne to the 14-electron
RuHClL2 species is thermodynamically highly favorable,
returning to the 14-electron vinyl is surprisingly also
slightly exothermic, which could be associated with the
poor electron-donating ability (i.e., π-basicity) of this Ru.
It should be kept in mind that all 14-electron species
This η2-vinyl complex undergoes an R-hydrogen mi-
gration to directly give the hydrido/vinylidene complex
in one step less than for Ru (i.e., 4Os is not a stationary
Os
point). The transition state TS3-5 is 13.9 kcal mol-1
are probably further stabilized by two agostic interac-
+ 22
above 3Os, indicating an easy reaction. The transition
state has a very open Cl-Os-C(1) angle (171.9°) and a
dihedral Cl-Os-C(1)-C(2) angle of 65.5°. The final
hydrido/vinylidene 5Os is wholly analogous to its Ru
analogue. Its formation is strongly exothermic, and in
particular, the difference in energy between 3Os and 5Os
is 20.1 kcal mol-1 while it was only 3.2 kcal mol-1
tions, as has been seen in Ru(Ph)(CO)L2
and
+ 20
IrH2L2
.
However, the hydrido/vinylidene is overall
the most stable of all isomers on the path due in part
to the very potent π-accepting ability of the vinylidene
ligand.
The initial step of the reaction for both metals is the
insertion into the metal-H bond. The associated tran-
sition states have similar geometries and not too dif-
ferent energies with respect to the alkyne complexes.
However, these transition states lead to strikingly
different intermediates. In the case of Os, the vinyl
complex is found to be η2-coordinated, while in the case
of Ru, the same ligand is σ-bonded (i.e., η1) to the metal.
Recent related examples show that Ru and Os may favor
different isomeric forms of the same compound. Thus,
everything else being equal, a carbene complex has been
isolated in the case Ru while an hydrido/carbyne has
been isolated for Os.25a Similarly, a vinyl/vinylidene
complex for Os is isolated while a butadienyl ligand
resulting from the formal coupling of the vinyl and
vinylidene ligands has been characterized for Ru.25b
While more studies are needed for a deeper understand-
ing of the reasons behind these differences, a pattern
already emerges: among several isomeric forms, Ru
favors the structure with the maximum number of C-C
and C-H bonds within the ligands while Os favors the
isomer with the maximum number of bonds (Os-C, Os-
H) to the metal. The two vinyl isomers calculated in
this work fit this pattern well: the C-C π bond is
maintained in the four-coordinated η1-vinyl Ru complex
while it is destroyed in the case of Os in favor of an
additional Os-C bond. That is (eq 4), the H* migration
destroys a Ru-C bond in a but destroys a CdC bond
and forms an Os-C π bond in b. This pattern is
between 4Ru and 5Ru
.
As in the case of Ru, the 1,2-migration is found to be
unlikely since the transition state is 22.2 kcal mol-1
above the highest transition state of the other path.
Rea ctivity of MHX(dCdCHR)L2 tow a r d Nu cleo-
p h iles. Addition of nucleophiles (CO, CNMe) to the
complexes MHX(dCdCHR)L2 induces migration of the
hydride back to the R-carbon atom of the vinylidene,
yielding vinyl derivatives. OsHCl(dCdCHSiMe3)(PiPr3)2
reacts with nucleophiles (L ) CO, CNMe) in the time
of mixing to give Os{(E)-CHdCHSiMe3}Cl(L)2(PiPr3)2
(eq 3).
OsHCl(dCdCHSiMe3)(PiPr3)2 + 2L f
Os{(E)-CHdCHSiMe3}Cl(L)2(PiPr3)2 (3)
The IR spectrum in C6D6 of Os{(E)-CHdCHSi-
Me3}Cl(CO)2(PiPr3)2 shows two ν(CO) bands of similar
intensity at 1996 and 1923 cm-1, indicating a cis
1
disposition of these ligands. In the H NMR spectra,
there are two peaks in the vinylic region, the one at
higher field shows up as a doublet (J H-H ) 21.3 Hz) of
triplets (by coupling with both phosphines) and the one
at lower field is a doublet (J H-H ) 21.3 Hz). The J H-H
coupling constant is clearly in the expected range for a
trans disposition of both hydrogens.
RuHI(dCdCHSiMe3)(PtBu2Me)2 reacts with excess
MeNC, giving [Ru{(E)-CHdCHSiMe3}(MeNC)3(PtBu2-
Me)2]I, which has trans phosphines and mer-MeNC
ligands. Addition of NaBAr′4 (Ar′ ) 3,5-bis(trifluoro-
methyl)phenyl) to a solution of [Ru{(E)-CHdCHSiMe3}-
(MeNC)3(PtBu2Me)2]I leaves the NMR signature of the
cation unchanged, proving that the iodide is not coor-
dinated.
It is known that OsHCl(dCdCHCy)(CO)(PiPr3)2 rear-
ranges to Os{(E)-CHdCHCy}Cl(CO)(PiPr3)2 in solution
after 3 days.5b The reactions described here probably
go via a similar mechanism upon coordination of one
nucleophile and are extremely accelerated by the pres-
ence of an excess of nucleophile.
relevant to a deeper understanding of catalysis, where
Ru plays a larger role than Os, by favoring new bonds
within ligands (e.g., polymerization).4
These reactions formally reverse the formation of the
vinylidene from a vinyl intermediate.
We show here an example of a low-barrier R-migra-
tion of H from C(1) to the metal in the transformation
of a vinyl into a hydrido vinylidene. The facile migra-
tion could be due to the fact that the two orbitals that
interchange electron occupancy in the transformation
Discu ssion
The reaction path suggested by the isotopic labeling
is shown to be energetically favorable from the calcula-
tions. The paths calculated for Ru and Os are exother-
mic from reactants to the final product (Figures 2 and
Ru
of 4Ru to 5Ru are dxy and dx -y (occupied in 4 and 5Ru
,
2
2
respectively). These two orbitals are of the same a′

3100 Organometallics, Vol. 17, No. 14, 1998
Oliva´n et al.
symmetry (Cs point group), making the transformation
feasible. Noteworthy is the fact that dxy, which will be
emptied on going to 5Ru as the C(1)-H(3) bond is
cleaved, is destabilized by the px lone pair of Cl and is,
thus, a powerful electron donor into σ*CH, as shown in
6.
observed facile conversions of eq 5 may occur preferably
via a bimolecular, not unimolecular, path.26
The title and conclusions of this paper apply equally
well to the reactions3d of RuHCl(H2)(PCy3)2 with vinyl
chlorides and propargyl halides: addition of the Ru-H
bond across the C/C unsaturation is the fastest reaction;
that is, C-halide cleavage occurs later.
Con clu sion s
This work proposes a new route for the formation of
a hydrido/vinylidene going through transformation of
a vinyl into a hydrido/vinylidene. The route is sup-
ported by isotopic labeling and theoretical studies of
several competing routes. It is also shown that although
Ru and Os have a similar energetic ability to form the
hydrido/vinylidene product, the nature of the intermedi-
ates on the path may be different. These differences
are consistent with related recent observations for Ru
and Os.
There are experimental indications18 and increasingly
frequent proposals that this R-H migration could be
facile.19 This is true although hydrido/vinylidene and
η1-vinyl have a different valence electron count. How-
ever, it was shown earlier that (1,3-) migration of H in
a hydrido acetylide complex (eq 5), to make a vinylidene,
has a high (33.5 kcal/mol) barrier; the same is true of
Ru
TS2-5
here (Figure 2). In the facile reaction of
RuHClL2 with alkynes, this high barrier is avoided by
first forming a vinyl complex (addition of Ru-H across
the CtC bond), followed by facile R-H migration from
the vinyl CR to Ru. No 1,3-H migration of eq 5 is
required since the oxidative addition of the C-H bond
of the primary alkyne to RuHClL2 is not energetically
feasible. The facile route, eq 6, through a vinyl complex
Ack n ow led gm en t. This work was supported by the
U.S. National Science Foundation and by the French
CNRS, in part by an international NSF/CNRS (PICS)
grant. M.O. thanks the Spanish Ministerio de Educacio´n
y Cultura for a postdoctoral fellowship. We also thank
J ohnson Matthey/Aesar for material support.
OM971109R
(26) Wakatsuki, Y.; Koga, N.; Werner, H.; Morokuma, K. J . Am.
Chem. Soc. 1997, 119, 360.
is thus preferred. As noted in a theoretical study, the