Isomerization of CH3C=CPh to phenylallene promoted by an osmium hydride complex

Article abstract of DOI:10.1021/om0004141

Treatment of OsH₃Cl(PPh₃)₃ in benzene with excess CH₃C=CPh produced cis-CH₃CH=CHPh and the novel complex OsCl(C(CH₃)=CHPh)(CH₂=C=CHPh)-(PPh₃) ₂, which contains a β-agostic vinyl ligand and a phenylallene ligand. The structure of the latter unusual complex has been confirmed by a single-crystal X-ray diffraction study.

Full text of DOI:10.1021/om0004141

3466
Organometallics 2000, 19, 3466-3468
Isom er iza tion of CH3CtCP h to P h en yla llen e P r om oted
by a n Osm iu m Hyd r id e Com p lex
Ting Bin Wen,† Zhong Yuan Zhou,‡ Chak-Po Lau,‡ and Guochen J ia*,†
Department of Chemistry, The Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong, China, and Department of Applied Biology and
Chemical Technology, Hong Kong Polytechnic University, Hong Kong, China
Received May 15, 2000
Summary: Treatment of OsH3Cl(PPh3)3 in benzene with
excess CH3CtCPh produced cis-CH3CHdCHPh and the
novel complex OsCl(C(CH3)dCHPh)(CH2dCdCHPh)-
(PPh3)2, which contains a â-agostic vinyl ligand and a
phenylallene ligand. The structure of the latter unusual
complex has been confirmed by a single-crystal X-ray
diffraction study.
Cp*Re(CO)2(MeCtCMe) (trifluoroacetic acid),10 and
CpMn(CO)2(cyclooctyne) (silica, basic and acidic alu-
mina)11 to allene complexes has been reported.
In acid-promoted isomerization of alkyne complexes
to allene complexes, 1-metallacyclopropene10 or η1-vinyl
species5 have been suggested as the key intermediates,
which may be formed by direct protonation of an alkyne
ligand10 or from the insertion reaction of an intermedi-
ate hydrido alkyne complex.5 In this regard, it would
be interesting to demonstrate that preformed hydride
complexes could also react with internal alkynes to give
allene complexes. During the investigation of the reac-
Terminal alkynes HCtCR are thermodynamically
more stable than their vinylidene forms :CdCHR.
However, many coordinatively unsaturated transition-
metal complexes LnM readily react with RCtCH to give
vinylidene complexes LnMdCdCHR rather than η2-
alkyne complexes LnM(η2-HCtCR).1 Repulsive interac-
tion of an alkyne π orbital with a filled metal d orbital
in LnM(η2-HCtCR) renders these complexes less stable
relative to the corresponding vinylidene complexes
LnMdCdCHR.2 The repulsive interaction should also
occur with internal alkynes R2CHCtCR′, and thus R2-
CHCtCR′ may isomerize to R2CdCdCHR′ on complex-
ation to certain transition-metal fragments. Isomeriza-
tion of alkynes to allenes is interesting because allenes
are useful precursors for organic synthesis,3 and because
the transformation may be involved in organometallic
synthesis.4-6 However, only a few reports on metal-
mediated isomerization of internal alkynes to allenes
have appeared, although examples of metal-mediated
isomerization of terminal alkynes to vinylidene are
numerous.1 Formation of allene complexes has been
reported in the reactions of ReCl(N2)(dppe)27 and RhCl-
12
tivity of OsH3Cl(PPh3)3 with alkynes, we have discov-
ered that the unusual complex OsCl(C(CH3)dCHPh)-
(CH2dCdCHPh)(PPh3)2 is produced from the reaction
of CH3CtCPh with OsH3Cl(PPh3)3. The transformation
appears to be the first example of reactions of preformed
hydride complexes with internal alkynes to give well-
defined allene complexes.
Treatment of OsH3Cl(PPh3)3 (1) in benzene with
excess CH3CtCPh at room temperature produced OsCl-
(C(CH3)dCHPh)(CH2dCdCHPh)(PPh3)2 (2) along with
the hydrogenated product cis-CH3CHdCHPh (Scheme
1).13 Compound 2 could also be obtained by reacting
12
OsHCl(PPh3)3 with excess CH3CtCPh at room tem-
perature. The structure of 2 has been confirmed by a
single-crystal X-ray diffraction study (Figure 1).14 It
reveals that two molecules of PhCtCCH3 have been
incorporated into the osmium center: one in the form
of the vinyl group PhCHdCCH3 and the other one in
the form of the phenylallene ligand PhCHdCdCH2.
Compound 2 represents the first structurally character-
ized mononuclear osmium allene complex. Another
8
(C2H4)(As(i-Pr)3)2 with internal alkynes. Acid-, silica-,
and alumina-promoted isomerization of preformed alkyne
complexes, such as (η5-MeC5H4)Mn(η2-RCtCR′) (basic
alumina oxide),9 CpRh(MeCtCMe)(P(i-Pr)3) (alumina),5
(10) Casey, C. P.; Brady, J . T. Organometallics 1998, 17, 4620.
(11) Coughlan, S. C.; Yang, G. K. J . Organomet. Chem. 1993, 450,
151.
† The Hong Kong University of Science and Technology.
‡ Hong Kong Polytechnic University.
(1) (a) Bruce, M. I. Chem. Rev. 1991, 91, 197. (b) Bruce, M. I.;
Swincer, A. G. Adv. Organomet. Chem. 1983, 22, 59. (c) Bruneau, C.;
Dixneuf, P. H. Acc. Chem. Res. 1999, 32, 311.
(2) Templeton, J . L. Adv. Organomet. Chem. 1989, 29, 1.
(3) (a) Schuster, H. F.; Coppola, G. M. Allenes in Organic Synthesis;
Wiley: New York, 1984. (b) Brandsma, L.; Verkruijsse, H. D. Synthesis
of Acetylenes, Allenes and Cumulenes, A Laboratory Manual; Elsevi-
er: Amsterdam, 1981.
(4) Leeaphon, M.; Ondracek, A. L.; Thomas, R. J .; Fanwick, P. E.;
Walton, R. A. J . Am. Chem. Soc. 1995, 117, 9715.
(5) Wolf, J .; Werner, H. Organometallics 1987, 6, 1164.
(6) Casey, C. P.; Brady, J . T.; Boller, T. M.; Weinhold, F.; Hayashi,
R. K. J . Am. Chem. Soc. 1998, 120, 12500.
(12) Ferrando, G.; Caulton, K. G. Inorg. Chem. 1999, 38, 4168.
(13) Preparation of 2. To a suspension of OsH3Cl(PPh3)3 (0.40 g, 0.39
mmol) in benzene (30 mL) was added CH3CtCPh (0.25 mL, 1.97
mmol). The reaction mixture was stirred at room temperature for 8 h
to give a brown solution. The solvent was pumped away under vacuum,
and the residue was redissolved in a minimum amount of CH2Cl2 (∼2
mL). A brownish yellow solid was formed when methanol (30 mL) was
slowly added to the residue. The solid was collected by filtration,
washed with methanol (2 × 20 mL) and hexane (2 × 20 mL), and dried
under vacuum overnight. Yield: 0.24 g, 63.1%. Anal. Calcd for C54H47
-
ClP2Os: C, 65.94; H, 4.82. Found: C, 65.36; H, 5.12. 31P{1H} NMR
(121.5 MHz, CDCl3): δ -6.3 (s). 1H NMR (300.13 MHz, CDCl3): δ 0.06
(br, 3 H, OsC(CH3)dC), 1.27 (br, 2 H, CH2dCdC), 5.41 (br, 1 H, OsC-
(CH3)dCHPh), 6.59 (br, 1 H, CH2dCdCHPh), 7.72∼7.07 (m, 40 H, Ph,
PPh3). 13C{1H} NMR (100.40 MHz, CD2Cl2): 155.06 (t, J (PC) ) 6.19
Hz, Os(η2-CH2dCdCHPh)), 154.13 (t, J (PC) ) 6.26 Hz, Os-C(CH3)d
C), 140.93-124.67 (m, Ph, PPh3), 122.99 (s, OsC(CH3)dCHPh), 119.86
(s, Os(η2-CH2dCdCHPh)), 8.31 (s, Os(η2-CH2dCdC)), 3.47 (s, OsC-
(CH3)dCHPh).
(7) Hughes, D. L.; Pombeiro, A. J . L.; Pickett, C. J .; Richards, R. L.
J . Chem. Soc. Chem. Commun. 1984, 992.
(8) Werner, H.; Schwab, P.; Mahr, N.; Wolf, J . Chem. Ber. 1992, 125,
2641.
(9) Frank-Neumann, M.; Brion, F. Angew. Chem., Int. Ed. Engl.
1979, 18, 688.
10.1021/om0004141 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 08/01/2000

Communications
Organometallics, Vol. 19, No. 18, 2000 3467
Consistent with the solid structure, the 31P{1H} NMR
spectrum of 2 in CDCl3 showed a singlet at -6.3 ppm.
In the 1H NMR spectrum, the allene proton signals were
observed at 1.27 (CH2) and 6.59 (dCHPh) ppm; the vinyl
proton signal was observed at 5.41 ppm. The methyl
proton signal was observed at 0.06 ppm. The chemical
shift is unusually upfield for typical CH3 attached to
an sp2-hybridized carbon but is consistent with the
presence of an agostic interaction. For comparison, the
signal of the methyl group with an agostic interaction
in [IrPh(C(CHdCHCMe3)dCHCMe3)(PMe3)3]PF6 was
observed at -0.7 ppm.19 Consistent with the existence
of the agostic interaction in 2, the 13C NMR spectrum
showed the CH3 signal at 3.47 ppm. For comparison,
the signal of the methyl group with an agostic interac-
tion in Cp*Ru(C(Me)dC(Me)CtCCMe3)(PPh3) was ob-
served at 4.5 ppm.17
We have monitored the reaction at low temperature
by 31P{1H} and 1H NMR in order to detect the inter-
mediates for the formation of complex 2 from the
reaction of OsH3Cl(PPh3)3 with 3.5 equiv of CH3CtCPh.
Below -13 °C in CD2Cl2, no appreciable reaction was
observed. At -8 °C, a new 31P signal at 16.9 ppm started
to appear along with that of free PPh3. The 1H NMR
spectrum of the newly formed osmium complex showed
a vinyl signal at 5.44 ppm and a CH3 signal at -0.88
ppm. Again, the chemical shift of the methyl group is
unusually upfield for typical CH3, implying the presence
F igu r e 1. Molecular structure for OsCl(C(CH3)dCHPh)-
(CH2dCdCHPh)(PPh3)2. The thermal ellipsoids are drawn
at the 40% probability level. Solvent molecules and the
hydrogen atoms of the phenyl rings are omitted for clarity.
Selected bond distances (Å) and angles (deg) are as fol-
lows: Os(1)-P(1), 2.3934(17); Os(1)-P(2), 2.3906(16); Os-
(1)-Cl(1), 2.4481(16); Os(1)-H(1A), 1.8110; Os(1)-C(1),
2.527(6); Os(1)-C(2), 2.023(6); Os(1)-C(10), 2.119(6); Os-
(1)-C(11), 1.993(6); C(1)-C(2), 1.519(8); C(2)-C(3), 1.314-
(8); C(10)-C(11), 1.389(8); C(11)-C(12), 1.347(8); P(1)-
Os(1)-P(2), 179.66(6); P(1)-Os(1)-Cl(1), 89.86(6); P(2)-
Os(1)-Cl(1), 90.47(6); P(1)-Os(1)-C(1), 89.75(14); P(2)-
Os(1)-C(1), 90.16(14); P(1)-Os(1)-C(2), 88.30(17); P(2)-
Os(1)-C(2), 91.43(17); C(1)-Os(1)-C(2), 36.9(2); C(10)-
Os(1)-P(1), 90.02(16), C(10)-Os(1)-P(2), 89.74(16); C(11)-
Os(1)-P(1), 90.45(16); C(11)-Os(1)-P(2), 89.52(16); C(10)-
Os(1)-C(11), 39.3(2); C(1)-Os(1)-C(10), 119.0(2); C(2)-
Os(1)-C(10), 82.1(2); C(1)-Os(1)-C(11), 158.3(2); C(2)-
Os(1)-C(11), 121.4(2); C(1)-Os(1)-Cl(1), 100.13(16); C(2)-
Os(1)-Cl(1), 137.02(18); C(10)-Os(1)-Cl(1), 140.89(18);
C(11)-Os(1)-Cl(1), 101.56(17); C(1)-C(2)-C(3), 128.0(6);
C(10)-C(11)-C(12), 141.7(6).
1
of an agostic interaction. The H NMR spectrum of the
newly formed osmium complex also showed two triplet
hydride signals (each integrated to one proton relative
to the vinyl signal) at -9.16 (J (PH) ) 15.0 Hz) and
-11.61 (J (PH) ) 15.0 Hz) ppm, indicating that the
complex only contains two PPh3 ligands. The spectro-
scopic data are consistent with the formation of
OsClH2(H3CCdCHPh)(PPh3)2 (3). When the tempera-
ture was increased to -1 °C, 1H signals due to com-
pound 2, cis-CH3CHdCHPh, and OsHCl(PPh3)3 ap-
peared. At this temperature, a minor singlet 31P{1H}
peak at 19.0 ppm could also be seen. After the reaction
temperature was raised to room temperature and the
reaction mixture was allowed to stand for 30 min, the
signals of complex 1 and 3 disappeared and the only
detectable species were OsHCl(PPh3)3 (major), PPh3, cis-
CH3CHdCHPh, complex 2 (minor), and a very minor
Sch em e 1
(14) Crystallographic details for 2 are as follows. Crystallographic
data for 2‚2C6H6: triclinic, space group P1h (No. 2), a ) 13.4250(18) Å,
b ) 14.6549(1) Å, c ) 15.1240(19) Å, R ) 84.868(3)°, â ) 88.023(3)°, γ
) 68.142(3)°, V ) 2750.5(6) Å3, Z ) 2, Dcalcd ) 1.376 g cm-3, Mo KR
radiation (λ ) 0.710 73 Å), µ ) 24.65 cm-1, crystal size 0.18 × 0.08 ×
0.08 mm3. Of 18 650 reflections collected (Bruker SMART CCD area
detector, 294 K), 12 484 were unique and 7560 were observed with I
> 2σ(I). The structure was solved by direct methods and refined by
full-matrix least squares on F2 using the Bruker SHELXTL (version
5.10) program package. All non-hydrogen atoms were refined aniso-
tropically. The H atoms, except those for the phenyl rings, were located
from the difference Fourier map and were constrained to ride on the
respective carbon after several cycles of refinement. The H atoms for
all phenyl rings were introduced at calculated positions and refined
2
via a riding model. The structure converged at RF ) 0.0543 and RwF
) 0.1120 (for all data).
interesting feature of the structure is that there exists
an agostic interaction between the osmium center and
one of the protons of the CH3 group of the vinyl ligand.
â-Agostic vinyl complexes are interesting, as they can
be regarded as the resting states for the interconversion
of allene and vinyl complexes.15,16 Well-characterized
â-agostic vinyl complexes are still rare,17 although
â-agostic alkyl complexes are numerous.18
(15) (a) Chin, C. S.; Cho, H.; Won, G.; Oh, M.; Ok, K. M. Organo-
metallics 1999, 18, 4810. (b). Chin, C. S.; Maeng, W.; Chong, D.; Won,
G.; Lee, B.; Park, Y. J .; Shin, J . M. Organometallics 1999, 18, 2210.
(16) (a) Brinkmann, P. H. P.; Luinstra, G. A.; Saenz, A. J . Am. Chem.
Soc. 1998, 120, 2854. (b) Gibson, V. C.; Parkin, G.; Bercaw, J . E.
Organometallics 1991, 10, 220.
(17) Yi, C. S.; Liu, N. Organometallics 1998, 17, 3158.
(18) Brookhart, M.; Green, M. L. H.; Wong, L. L. Prog. Inorg. Chem.
1988, 36, 1 and references therein.
(19) Selnau, H. E.; Merola, J . S. J . Am. Chem. Soc. 1991, 113, 4008.

3468 Organometallics, Vol. 19, No. 18, 2000
Communications
CH2)2(PPh3)2.12 Intermediate A undergoes an insertion
reaction to give the vinyl complex B.21 Oxidative addi-
tion of one of the C-D bonds of the vinyl group in B
would produce the deuteride complex C, which then
undergoes another insertion reaction to give the final
product 2d 6. Although the hydride and vinyl intermedi-
ates have not been detected, similar reaction sequences
have been proposed for the formation of RhCl(CH2dCd
CH2)(As(i-Pr)3)2 from the reaction of RhCl(C2H4)(As(i-
Pr)3)2 with HCtCMe8 and for the formation of [CpRh(η3-
CH3CHCHCH2)(P(i-Pr)3)]+from protonation ofCpRh(MeCt
CMe)(P(i-Pr)3).5 A related reaction mechanism has been
proposed for the reaction of Os(CD2Ph)(CtCPh)(CO)2-
(P(i-Pr)3)2 with HBF4 to give [Os(η3-PhCHCDCDPh)-
(CO)2(P(i-Pr)3)2]BF4.22 It should be noted that 1-metal-
lacyclopropene rather than a η1-vinyl species is involved
in the formation of [Cp*Re(CO)2(η3-CH3CHCHCH2)]+
from protonation of Cp*Re(CO)2(MeCtCMe)6 and in the
formation of Cp*Re(CO)2(CH2dCdCMe) from acid-
catalyzed isomerization of Cp*Re(CO)2(MeCtCMe).10 In
the latter case, the allene ligand is more likely formed
by direct deprotonation of metallacyclopropene rather
than â-hydrogen elimination.
Sch em e 2
In summary, we have shown that reaction of CH3-
CtCPh with OsH3Cl(PPh3)3 produced the unusual
complex OsCl(C(CH3)dCHPh)(CH2dCdCHPh)(PPh3)2,
which contains a â-agostic vinyl ligand and a phenyl-
allene ligand. The vinyl complex formed by insertion of
H3CtCPh into a Os-H bond appears to be the key
intermediate for the formation of the allene ligand.
Structurally characterized â-agostic vinyl ligands are
interesting, as related species may be involved in the
interconversion of allene and vinyl complexes. We are
currently exploring the scope and uses of the interesting
reactions.
amount of an unknown species having a 31P signal at
19.0 ppm. OsHCl(PPh3)3 was completely converted to
compound 2 when the reaction mixture was allowed to
stand at room temperature for 8 h.
To further understand the mechanism for the forma-
tion of complex 2, we have reacted OsH3Cl(PPh3)3 with
2
CD3CtCPh under similar conditions. H NMR of the
isolated product shows that OsCl(C(CD3)dCDPh)-
(CD2dCdCHPh)(PPh3)2 was formed exclusively (see
Scheme 1).20 The results strongly suggest that the allene
ligand is not formed by a simple 1,3-hydrogen shift and
that the vinyl ligand is not formed by simple insertion
of CH3CtCPh into an Os-H bond.
A plausible sequence for the formation of complex 2
is illustrated in Scheme 2 using D3CCtCPh as the
substrate. Reaction of OsH3Cl(PPh3)3 with the first
equivalent of D3CCtCPh gives OsHCl(PPh3)3 and cis-
CD3CHdCHPh through intermediate 3d 3, which has
Ack n ow led gm en t. We acknowledge financial sup-
port from the Hong Kong Research Grants Council.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic details, bond distances and angles, atomic coordi-
nates and equivalent isotropic displacement coefficients, and
anisotropic displacement coefficients for OsCl(C(CH3)dCHPh)-
(CH2dCdCHPh)(PPh3)2‚2C6H6. The material is available free
of charge via the Internet at http://pubs.acs.org.
1
been detected by 31P{1H} and H NMR at low temper-
ature. OsHCl(PPh3)3 can then react with additional D3-
CCtCPh to give the bis(alkyne) intermediate A. For-
mation of A is reasonable, as reaction of OsH3Cl(PPh3)3
with excess ethylene gives ethane and OsHCl(CH2d
OM0004141
(20) OsCl(C(CD3)dCDPh)(CD2dCdCHPh)(PPh3)2 (2d 6) was pre-
pared by the same procedure, with the use of CD3CtCPh instead of
CH3CtCPh. CD3CtCPh was prepared by addition of CD3I in THF at
dry ice/acetone temperature to a freshly prepared solution of lithium
phenylacetylide in THF and hexane (1:1). The LiCtCPh was in turn
prepared by adding phenylacetylene to a fresh solution of butyllithium
in hexane and THF (1:1) at 0 °C. Selected characterization data for
2d 6: 31P{1H} NMR (121.5 MHz, CDCl3) δ -6.13 (s); 1H NMR (399.65
MHz, CDCl3) δ 6.36 (br, 1H, CD2dCdCHPh), 7.50∼6.83 (m, 40 H, Ph,
PPh3); 2H NMR (61.25 MHz, CHCl3) δ -0.11 (br, 3 D, OsC(CD3)d
CDPh), 1.11 (br, 2 D, Os(η2-CD2dCdCHPh), 5.31 (br, 1D, OsC(CD3)d
CDPh).
(21) For recent examples of insertion of alkynes into an Os-H bond,
see for example: (a) Oliva´n, M.; Clot, E.; Eisenstein, O.; Caulton, K.
G. Organometallics 1998, 17, 3091. (b) Huang, D.; Oliva´n, M.; Huffman,
J . C.; Eisenstein, O.; Caulton, K. G. Organometallics 1998, 17, 4700.
(c) Buil, M. L.; Esteruelas, M. A. Organometallics 1999, 18, 1798. (d)
Bohanna, C.; Callejas, B.; Edwards, A. J .; Esteruelas, M. A.; Lahoz,
F. J .; Oro, L. A.; Ruiz, N.; Valero, C. Organometallics 1998, 17, 373
and references therein. (e) Esteruelas, M. A.; Oro, L. A.; Valero, C.
Organometallics 1995, 14, 3596.
(22) Buil, M. L.; Esteruelas, M. A.; Lo´pez, A. M.; On˜ate, E.
Organometallics 1997, 16, 3169.