First x-ray characterization and theoretical study of π-alkyne, alkynyl-hydride, and vinylidene isomers for the same transition metal fragment [Cp*Ru(PEt3)2]+

Article abstract of DOI:10.1021/ja0291181

The reaction of the chloro-complex [Cp*RuCl(PEt₃)₂] with acetylene gas in methanol gave the π-alkyne complex [Cp*Ru(η²-HC≡CH) (PEt₃)₂][BPh₄] (1), which has been structurally characterized by X-ray analysis. The alkyne complex undergoes spontaneous isomerization even at low temperature, yielding the metastable alkynyl-hydride complex [Cp*Ru(H)(C≡CH)(PEt₃)₂][BPh₄] (2), as the result of the oxidative addition of the alkyne C-H bond. This compound has also been structurally characterized despite it tautomerizes spontaneously into the stable primary vinylidene [Cp*Ru(=C=CH₂)(PEt₃)₂] [BPh₄] (3). This species has been alternatively prepared by a two-step deprotonation/protonation synthesis from the π-alkyne complex. Moreover, the reaction of the initial chloro-complex with monosubstituted alkynes HC≡CR (R = SiMe₃, Ph, COOMe, ^tBu) has been studied without detection of π-alkyne intermediates. Instead of this, alkynyl-hydride complexes were obtained in good yields. They also rearrange to the corresponding substituted vinylidenes. In the case of R = SiMe₃, the isomerization takes place followed by desilylation, yielding the primary vinylidene complex. X-ray crystal structures of the vinylidene complexes [Cp*Ru(= C=CH₂)(PEt₃)₂][BPh₄] (3) and [Cp*Ru(=C=CHCOOMe)(PEt₃)₂][BPh₄] (10) have also been determined. Both, full ab initio and quantum mechanics/molecular mechanics (QM/MM) calculations were carried out, respectively, on the model system [CpRu(C₂H₂)(PH₃)₂]⁺ (A) and the real complex [Cp*Ru(C₂H₂) (PEt₃)₂]⁺ (B) to analyze the steric and electronic influence of ligands on the structures and relative energies of the three C₂H₂ isomers. QM/MM calculations have been employed to evaluate the role of the steric effects of real ligands, whereas full ab initio energy calculations on the optimized QM/MM model have allowed recovering the electronic effects of ligands. Additional pure quantum mechanics calculations on [Cp*Ru(C₂H₂) (PH₃)₂]⁺ (C) and [CpRu(C₂H₂)(PMe₃)₂]⁺ (D) model systems have been performed to analyze in more detail the effects of different ligands. Calculations have shown that the steric effects induced by the presence of bulky substituents in phosphine ligand are responsible for experimentally observed alkyne distortion and for relative destabilization of the alkyne isomer. Moreover, increasing the phosphine basicity and σ donor capabilities of ligands causes a relative stabilization of an alkynyl-hydride isomer. The combination of both steric and electronic effects, makes alkyne and alkynyl-hydride isomers to be close in energy, leading to the isolation of both complexes.

Full text of DOI:10.1021/ja0291181

Published on Web 02/22/2003
First X-ray Characterization and Theoretical Study of
π-Alkyne, Alkynyl-Hydride, and Vinylidene Isomers for the
Same Transition Metal Fragment [Cp*Ru(PEt3)2]+
Emilio Bustelo, Jorge J. Carbo´,† Agust´ı Lledo´s,† Kurt Mereiter,‡
M. Carmen Puerta, and Pedro Valerga*
Contribution from the Departamento de Ciencia de los Materiales, Ingenier´ıa Metalu´rgica y
Qu´ımica Inorga´nica, UniVersidad de Ca´diz, Apdo. 40, 11510 Puerto Real, Ca´diz, Spain,
Departament de Qu´ımica, UniVersitat Auto`noma de Barcelona, 08193 Bellaterra,
Barcelona, Spain, and Institute of Chemical Technologies and Analytics,
Vienna UniVersity of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
Received October 28, 2002; Revised Manuscript Received January 14, 2003; E-mail: pedro.valerga@uca.es
Abstract: The reaction of the chloro-complex [Cp*RuCl(PEt3)2] with acetylene gas in methanol gave the
π-alkyne complex [Cp*Ru(η2-HCtCH)(PEt3)2][BPh4] (1), which has been structurally characterized by X-ray
analysis. The alkyne complex undergoes spontaneous isomerization even at low temperature, yielding the
metastable alkynyl-hydride complex [Cp*Ru(H)(CtCH)(PEt3)2][BPh4] (2), as the result of the oxidative
addition of the alkyne C-H bond. This compound has also been structurally characterized despite it
tautomerizes spontaneously into the stable primary vinylidene [Cp*Ru(dCdCH2)(PEt3)2][BPh4] (3). This
species has been alternatively prepared by a two-step deprotonation/protonation synthesis from the π-alkyne
complex. Moreover, the reaction of the initial chloro-complex with monosubstituted alkynes HCtCR (R )
t
SiMe3, Ph, COOMe, Bu) has been studied without detection of π-alkyne intermediates. Instead of this,
alkynyl-hydride complexes were obtained in good yields. They also rearrange to the corresponding
substituted vinylidenes. In the case of R ) SiMe3, the isomerization takes place followed by desilylation,
yielding the primary vinylidene complex. X-ray crystal structures of the vinylidene complexes [Cp*Ru(d
CdCH2)(PEt3)2][BPh4] (3) and [Cp*Ru(dCdCHCOOMe)(PEt3)2][BPh4] (10) have also been determined.
Both, full ab initio and quantum mechanics/molecular mechanics (QM/MM) calculations were carried out,
respectively, on the model system [CpRu(C2H2)(PH3)2]+ (A) and the real complex [Cp*Ru(C2H2)(PEt3)2]+
(B) to analyze the steric and electronic influence of ligands on the structures and relative energies of the
three C2H2 isomers. QM/MM calculations have been employed to evaluate the role of the steric effects of
real ligands, whereas full ab initio energy calculations on the optimized QM/MM model have allowed
recovering the electronic effects of ligands. Additional pure quantum mechanics calculations on [Cp*Ru-
(C2H2)(PH3)2]+ (C) and [CpRu(C2H2)(PMe3)2]+ (D) model systems have been performed to analyze in more
detail the effects of different ligands. Calculations have shown that the steric effects induced by the presence
of bulky substituents in phosphine ligand are responsible for experimentally observed alkyne distortion
and for relative destabilization of the alkyne isomer. Moreover, increasing the phosphine basicity and σ
donor capabilities of ligands causes a relative stabilization of an alkynyl-hydride isomer. The combination
of both steric and electronic effects, makes alkyne and alkynyl-hydride isomers to be close in energy,
leading to the isolation of both complexes.
Introduction
a renewed interest coming from both experimental and theoreti-
cal points of view. In particular, some well-known complexes
Activation of alkynes by transition-metal complexes has
attracted considerable attention during the past few decades. In
this context, Ru-catalyzed reactions of alkynes and related
stoichiometric reactions have been extensively developed.1 In
the last years, the acetylene-vinylidene rearrangement has gained
have been revisited. Such is the case with [CpMn(C2H2)(CO)2]2
or [(PP3)Co(C2H2)]+ (PP3 ) P(CH2CH2PPh2)3),3 and even new
insights for the free rearrangement of acetylene have been
reported.4 The study of the alkyne-vinylidene isomerization is
constantly broadened toward systems with different metals5 or
† Universitat Auto`noma de Barcelona.
‡ Vienna University of Technology.
(2) (a) Silvestre, J.; Hoffmann, R. HelV. Chim. Acta 1985, 68, 1461. (b) De
Angelis, F.; Sgamellotti, A.; Re, N. Organometallics 2002, 21, 2715.
(3) (a) Bianchini, C.; Peruzzini, M.; Vacca, A.; Zanobini, F. Organometallics
1991, 10, 3697. (b) Pe´rez-Carren˜o, E.; Paoli, P.; Ienco, A.; Mealli, C. Eur.
J. Inorg. Chem. 1999, 8, 1315.
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123, 641.
(1) For recent reviews, see: (a) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem.
ReV. 1998, 98, 2599. (b) Bruneau, C.; Dixneuf, P. H. Acc. Chem. Res.
1999, 32, 311. (c) Puerta, M. C.; Valerga, P. Coord. Chem. ReV. 1999,
193-195, 977. (d) Trost, B. M.; Toste, D.; Pinkerton, A. B. Chem. ReV.
2001, 101, 2067. (e) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. ReV. 2002,
102, 1731.
9
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J. AM. CHEM. SOC. 2003, 125, 3311-3321
3311

A R T I C L E S
Bustelo et al.
as PEt3, gave similar results in reaction with alkynols.13 The
present paper describes new outcomes from the activation of
acetylene and 1-alkynes with [Cp*RuCl(PEt3)2], and reports the
X-ray structural characterization of π-alkyne, alkynyl-hydride,
and vinylidene isomers. To the best of our knowledge, this is
the first time that those three C2H2 isomers have been structur-
ally characterized for the same transition metal complex and
the same alkyne. Besides that, we have carried out pure quantum
mechanics (QM) calculations on the [CpRu(C2H2)(PH3)2]+ (A)
model system. We have combined the pure quantum mechanics
calculations with quantum mechanics/molecular mechanics
(QM/MM) calculation on the [Cp*Ru(C2H2)(PEt3)2]+ (B) real
system in order to asses the steric effects of real ligands.
Furthermore, full ab initio energy calculations on the optimized
QM/MM model have been performed to recover the electronic
effect of real ligands. Additionally, pure quantum mechanics
calculations on [Cp*Ru(C2H2)(PH3)2]+ (C) and [CpRu(C2H2)-
(PMe3)2]+ (D) models have been employed to analyze in more
detail the effects of the different ligands. The combination of
methods and model systems has allowed us to separate, identify
and evaluate the different effects of ligands on the structure
and relative energies of the three C2H2 isomers. Thus, the
theoretical study has focused on the structural and energetic
properties of these three isomers, whereas the detailed kinetic
study of the alkyne-vinylidene isomerization is out of the
purpose of the current work.
Scheme 1
with new auxiliary ligands.6 In the case of Ru and Os complexes
a number of papers dealing with the role of the metallic
fragment, auxiliary ligands or alkyne substituents on such
process, has been reported.6-8
The isomerization mechanism into vinylidene has been
proposed to proceed via π-alkyne intermediates although they
are seldom isolated or even detected. The ulterior tautomeriza-
tion may occur through two alternative pathways (Scheme 1).
A first reasonable approach involves an active role of the metal
center, which undergoes the oxidative addition of the alkyne,
furnishing an intermediate alkynyl-hydride complex (Scheme
1-A). This pathway is competitive with a direct 1,2-hydrogen
shift in the former alkyne complex (Scheme 1-B), depending
on the particular metallic fragment. The second of these
mechanisms seems to predominate within the ruthenium chem-
istry. A direct isomerization of this type has been described by
Selegue et al, reporting the first structurally characterized pair
of C2H2 isomers, namely π-alkyne and vinylidene.9 On the other
hand, several examples and ab initio MO calculations support
the mechanism through alkynyl-hydride intermediates in the
chemistry of Co,3 Rh and Ir.10
Our contribution to this field started from the isolation of
the first ruthenium alkynyl-hydride complex [Cp*Ru(H)-
(CtCR)(dippe)]+ (dippe ) 1,2-bis(diisopropylphosphine)-
ethane), as metastable intermediate in the synthesis of the
corresponding vinylidene isomer.11 This result has been extended
to a number of alkynes and alkynols.12 The substitution of the
diphosphine dippe for two monodentate phophine ligands such
Results and Discussion
Synthesis and Characterization of π-Alkyne, Alkynyl-
Hydride and Vinylidene Species. Acetylene Activation. In
our previous studies, the isolation of metastable alkynyl-hydride
intermediates has been possible due to the high insolubility of
these cationic complexes as BPh4 salt in MeOH.11-13 Thus, the
reaction of [Cp*RuCl(PEt3)2] and acetylene has been carried
out by bubbling acetylene gas through a NaBPh4 solution in
MeOH, to which the chloro-complex was finally added. This
sequence causes the immediate precipitation of the yellow
compound [Cp*Ru(η2-HCtCH)(PEt3)2][BPh4] (1), in 85%
yield. Complex 1 is stable in the solid state at room temperature.
The IR spectrum exhibits the ν(CtC) band at 1732 cm-1. The
NMR spectra were recorded at -20 °C to prevent isomerization,
displaying phosphorus-coupled triplets at 4.38 and 66.14 ppm
(5) (a) (Nb): Garc´ıa Yebra, C.; Lo´pez Mardomingo, C.; Fajardo, M.; Antin˜olo,
A.; Otero, A.; Rodr´ıguez, A.; Vallat, A.; Lucas, D.; Mugnier, Y.; Carbo´, J.
J.; Lledo´s, A.; Bo, C. Organometallics 2000, 19, 1749. (b) (W): Stegmann,
R.; Frenking, G. Organometallics 1998, 17, 2089. (c) (Ta): Gibson, V.
C.; Parkin, G.; Bercaw, J. E. Organometallics 1991, 10, 220. (d) (Cr):
Bartlett, I. M.; Connelly, N. G.; Martin, A. J.; Orpen, A. G.; Paget, T. J.;
Rieger, A. L.; Rieger, P. H. J. Chem. Soc., Dalton Trans. 1999, 691. (e)
(Pt): Ara, I.; Berenguer, J. R.; Eguiza´bal, E.; Fornie´s, J.; Go´mez, J.; Lalinde,
E.; Sa´ez-Rocher, J. M. Organometallics 2000, 19, 4385.
1
for the C2H2 unit in the H and 13C{1H} spectra, respectively.
(6) Katayama, H.; Wada, C.; Taniguchi, K.; Ozawa, F. Organometallics 2002,
21, 3285.
In solution, compound 1 rearranges spontaneously at tem-
peratures above -20 °C. The process has been monitored by
31P{1H} NMR at -10 °C and the initial signal at 23.8 ppm
was slowly replaced by a new one at 37.7 ppm, corresponding
to the alkynyl-hydride isomer described later. This fact explains
why the recrystallization of 1 from an acetone/ethanol mixture
at low temperature yielded a major amount of crystals of the
second isomer. However, among them it was possible to identify
and separate a minor amount of crystals of complex 1 (with
the same color but slightly different shape). The X-ray structure
of 1 has been determined, being one of the scarce half-sandwich
ruthenium alkyne complexes structurally characterized.9,14 An
(7) (Ru): (a) Wakatsuki, Y.; Koga, N.; Yamazaki, H.; Morokuma, K. J. Am.
Chem. Soc. 1994, 116, 8105. (b) Cadierno, V.; Gamasa, M. P.; Gimeno,
J.; Pe´rez-Carren˜o, E.; Garc´ıa-Granda, S. Organometallics 1999, 18, 2821.
(c) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Gonza´lez-Bernardo, C.; Perez-
Carrero, E.; Garcia-Granda, S. Organometallics 2001, 20, 5177. (d)
Tokunaga, M.; Suzuki, T.; Koga, N.; Fukushima, T.; Horiuchi, A.;
Wakatsuki, Y. J. Am. Chem. Soc. 2001, 123, 11 917. (e) De Angelis, F.;
Sgamellotti, A.; Re, N. Organometallics, 2002, 21, 5944.
(8) (Os): (a) Esteruelas, M. A.; Lo´pez, A. M.; Ruiz, N.; Tolosa, J. I.
Organometallics 1997, 16, 4657. (b) Crochet, P.; Esteruelas, M. A.; Lo´pez,
A. M.; Ruiz, N.; Tolosa, J. I. Organometallics 1998, 17, 3479. (c) Oliva´n,
M.; Clot, E.; Eisenstein, O.; Caulton, K. G. Organometallics 1998, 17,
3091. (d) Baya, M.; Crochet, P.; Esteruelas, M. A.; Gutie´rrez-Puebla, E.;
Lo´pez, A. M.; Modrego, J.; On˜ate, E.; Vela, N. Organometallics 2000, 19,
2585. (e) Baya, M.; Crochet, P.; Esteruelas, M. A.; Lo´pez, A. M.; Modrego,
J.; On˜ate, E. Organometallics 2001, 20, 4291.
(9) Lomprey, J. R.; Selegue, J. P. J. Am. Chem. Soc. 1992, 114, 5518.
(10) (a) Werner, H. J. Organomet. Chem. 1994, 475, 45. (b) Werner, H.; Baum,
M.; Schneider, D.; Windmu¨ller, B. Organometallics 1994, 13, 1089. (c)
H. Werner, R. W. Lass, O. Gevert, J. Wolf, Organometallics 1997, 16,
4077. (d) Wakatsuki, Y.; Koga, N.; Werner, H.; Morokuma, K. J. Am.
Chem. Soc. 1997, 119, 360.
(12) (a) Bustelo, E.; de los R´ıos, I.; Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga,
P. Monatsh. Chem. 2000, 131, 1311. (b) Bustelo, E.; Jime´nez-Tenorio, M.;
Puerta, M. C.; Valerga, P. Eur. J. Inorg. Chem. 2001, 2391.
(13) (a) Bustelo, E.; Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. Organo-
metallics 1999, 18, 950. (b) Bustelo, E.; Jime´nez-Tenorio, M.; Puerta, M.
C.; Valerga, P.Organometallics 1999, 18, 4563.
(11) de los R´ıos, I.; Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. J. Am.
Chem. Soc. 1997, 119, 6529.
9
3312 J. AM. CHEM. SOC. VOL. 125, NO. 11, 2003

π-Alkyne, Alkynyl-Hydride, and Vinylidene Isomers
A R T I C L E S
Figure 2. Alkyne rotational orientation in [CpRu(PMe2Ph)2]+ 9 and
[Cp*Ru(PEt3)2]+ (1).
Figure 1. ORTEP drawing (50% thermal ellipsoids) of the cation [Cp*Ru-
(η2-HCtCH)(PEt3)2]+ (1).
Table 1. Selected Bond Lengths (Å) for Compounds 1, 2, and 3
with Estimated Standard Deviations in Parentheses
bond distances (Å)
1
2
3
Ru(1) P(1) 2.343(1) Ru(1) P(1) 2.346(1) Ru(1) P(1) 2.350(2)
Ru(1) P(2) 2.347(1) Ru(1) P(2) 2.328(1) Ru(1) P(2) 2.335(2)
Ru(1) C(23) 2.182(4) Ru(1) C(23) 2.034(4) Ru(1) C(1) 1.835(8)
Ru(1) C(24) 2.180(5) C(23) C(24) 1.150(6) C(1) C(2) 1.296(11)
C(23) C(24) 1.220(7) Ru(1) H(1) 1.33(4)
Figure 3. ORTEP drawing (50% thermal ellipsoids) of [Cp*Ru(H)-
(CtCH)(PEt3)2]+ (2).
ORTEP15 view of the cationic complex 1 is depicted in Figure
1. Selected bond lengths and angles are listed in Tables 1 and
2.
The geometry around the ruthenium atom in 1 can be
described as a three-legged piano-stool. The alkyne ligand is
symmetrically bound to the ruthenium atom (2.180(5) and 2.182-
(4) Å). The C(23)-C(24) distance (1.220(7) Å) is slightly longer
than the average value in free alkynes (1.18 Å).16
The rotational orientation of the alkyne unit relative to the
[Cp*Ru(PEt3)2] moiety is not orthogonal to the idealized mirror
plane (see Figure 2), although such disposition has been
predicted by qualitative MO reasoning.17 Therefore, the torsion
angles Cp-Ru-Mp-C(23) or Cp-Ru-Mp-C(24) (Cp, ring
centroid; Mp, alkyne CtC midpoint) of 69.3° and - 110.7°
are far from an ideally perpendicular alkyne (90° and - 90°).
This situation, although less pronounced, has also been reported
by Selegue et al. for the complex [CpRu(η2-HCtCH)(PMe2-
Ph)2]+ (98.5° and -81.5°).9 Discussions on the reason of the
discrepancy will be provided later on the basis of theoretical
calculations.
The alkynyl-hydride complex [Cp*Ru(H)(CtCH)(PEt3)2]-
[BPh4] (2) has been prepared by spontaneous isomerization of
1 at temperatures below 10 °C, to prevent the ulterior isomer-
ization into the thermodynamically favored vinylidene isomer.
Thus, compound 2 was obtained as a pale yellow solid in
quantitative yield. It exhibits the ν(CtC) and ν(Ru-H) bands
at 1967 and 1935 cm-1, respectively in the IR spectrum. The
31P{1H} NMR spectrum, recorded in CDCl3 at 5 °C, consists
1
of a singlet at 37.7 ppm. The hydride ligand appears in the H
NMR spectrum as a triplet at -9.27 ppm with a coupling
constant of 29.5 Hz, whereas the terminal alkynyl hydrogen
gives rise to a triplet at 2.09 ppm (4JHP ) 2.7 Hz). In the 13C-
{1H} NMR spectrum, a triplet at 93.09 ppm and a singlet at
102.1 ppm match well with the resonances expected for R and
â carbons of the alkynyl ligand. Yellow crystals corresponding
to the alkynyl-hydride isomer were obtained from the recrys-
tallization of 1 as described previously. Figure 3 shows the X-ray
structure of 2. Selected bond distances and angles are listed in
Tables 1 and 2.
The geometry around the ruthenium atom in the cationic
complex 2 can be described as a four-legged piano-stool, where
the hydride and alkynyl ligands are in transoid disposition with
a C(23)-Ru-H(1) angle of 131.3(16)°. The alkynyl ligand is
almost linearly assembled to ruthenium, being the Ru-C(23)-
C(24) angle 178.2(4)°. The P(1)-Ru-P(2) angle of 107.20-
(4)° is higher than that found for the analogous complex with
the chelating phosphine dippe (87.5°).11 The distances Ru-
C(23) (2.034(4) Å) and C(23)-C(24) (1.150(6) Å) correspond
to a single and triple bond, respectively.
The alkynyl-hydride complex 2 rearranges spontaneously to
the vinylidene isomer. In the solid state such process occurs
very slowly at room temperature, as observed for the analogous
alkynyl-hydride complex with the diphosphine dippe.12a In
solution, the process takes place perceptibly at temperatures
above 10 °C. Unfortunately, a clean synthesis of the vinylidene
is not possible when temperature reaches 20 °C. Otherwise, a
mixture of uncharacterized products is obtained probably owing
to side-reactions coming from the reactivity of the alkynyl
terminal hydrogen.
(14) (a) Bullock, R. M. J. Chem. Soc., Chem. Commun. 1989, 165. (b) Urtel,
K.; Frick, A.; Huttner, G.; Zsolnai, L.; Kircher, P.; Rutsch, P.; Kaifer, E.;
Jacobi, A. Eur. J. Inorg. Chem. 2000, 33.
(15) Johnson, C. K. ORTEP, A Thermal Ellipsoid Plotting Program; Oak Ridge
National Laboratory: Oak Ridge, Tennessee, 1965.
(16) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.;
Taylor, R. J. Chem. Soc., Perkin Trans. 1987, S1.
(17) Schilling, B. E. R.; Hoffmann, R.; Lichtenberger, D. L. J. Am. Chem. Soc.
1979, 101, 585.
9
J. AM. CHEM. SOC. VOL. 125, NO. 11, 2003 3313

A R T I C L E S
Bustelo et al.
Table 2. Selected Angles (deg) for Compounds 1, 2, and 3 with Estimated Standard Deviations in Parentheses
bond angles (deg)
1
2
3
P(1)Ru(1)P(2)
93.67(4)
P(1)Ru(1)P(2)
107.20(4)
79.93(12)
84.19(14)
178.2(4)
P(1)Ru(1)P(2)
P(1)Ru(1)C(1)
P(2)Ru(1)C(1)
Ru(1)C(1)C(2)
96.85(7)
87.6(3)
94.3(3)
P(1)Ru(1)C(24)
P(2)Ru(1)C(23)
C(23)Ru(1)C(24)
81.28(13)
79.87(14)
32.47(19)
P(1)Ru(1)C(23)
P(2)Ru(1)C(23)
Ru(1)C(23)C(24)
C(23)Ru(1)H(1)
171.8(8)
131.3(16)
Scheme 2
Figure 4. ORTEP drawing (50% thermal ellipsoids) of [Cp*Ru(dCdCH2)-
(PEt3)2]+ (3).
The isolation and structural characterization of the three
isomers for the same transition metal fragment, resulting from
the acetylene activation by [Cp*RuCl(PEt3)2], is particularly
noteworthy because the relative stabilities of such species are
usually opposed. Thus, in electron-rich complexes, the vi-
nylidene is the most stable isomer and even the detection of
any intermediate species is not possible. This is very clear in
the case of the alkyne isomer, which is always proposed as a
necessary intermediate in the isomerization process to vi-
nylidene. However, they are seldom isolated as the kinetic
product only when small alkyne substituents and small ancillary
ligands on the ruthenium are present.9,14a Data from a DFT
analysis on the three isomers relative energies will be provided
and discussed later.
Activation of 1-Alkynes. The activation of a number of
1-alkynes by [Cp*RuCl(PEt3)2] leads directly to the alkynyl-
hydride complexes [Cp*Ru(H)(CtCR)(PEt3)2][BPh4] (R )
SiMe3 (5), Ph (6), COOMe (7), tBu (8)). Attempts to detect by
31P{1H} NMR the initial formation in solution of π-1-alkyne
species failed.
The preparation of 5-8 has been carried out by a method
analogous to that described in the synthesis of 1 (see Scheme
3). The presence of NaBPh4 causes the immediate precipitation
of a pale yellow solid in MeOH, avoiding the isomerization to
the most stable vinylidene isomer. The IR spectra show in all
cases a strong absorption around 2100 cm-1, corresponding to
the alkynyl ν(CtC) band. The 1H NMR spectra exhibit a triplet
around -9.10 ppm for the hydride ligand, with coupling
constants of 27-30 Hz. In the 13C{1H} NMR spectra of 5-7,
signals for the alkynyl R and â carbons appear in the range
100-122 ppm.
An alternative procedure has been employed to prepare the
primary vinylidene [Cp*Ru(dCdCH2)(PEt3)2][BF4] (3) by the
stepwise deprotonation and protonation of 1. Treatment of
t
1 with BuOK yielded the neutral alkynyl complex [Cp*Ru-
(CtCH)(PEt3)2] (4) as a yellow solid. The IR ν(CtC) band
appears at 1942 cm-1. The NMR spectra display a triplet for
the alkynyl proton at 2.05 ppm, and a triplet and a singlet for
the alkynyl carbons at 108.9 and 91.29 ppm, respectively.
Protonation of 4 with HBF4‚Et2O occurs selectively on the
alkynyl â carbon atom, giving exclusively the vinylidene isomer
3. However, the most convenient method for the preparation of
3 is the direct activation of trimethylsilylacetylene by [Cp*RuCl-
(PEt3)2]. Therefore, complex 3 can be prepared in one step with
90% yield as a BPh4 salt. A summary of the preparative
procedures of complexes 1-4 is depicted in Scheme 2.
Recrystallization of complex 3 yielded orange crystals suitable
for XRD analysis and the crystalline structure was determined,
thereby completing the characterization of the isomers triad:
alkyne, alkynyl-hydride, and vinylidene. Figure 4 shows an
ORTEP view of the cationic complex 3. Selected bond lengths
and angles are listed in Tables 1 and 2.
The geometry around the ruthenium center can be described
as a three-legged piano-stool. The distances Ru-C(1) of 1.835-
(8) Å and C(1)-C(2) of 1.296(11) Å, are typical values for a
vinylidene ligand, which is almost linearly assembled to
ruthenium (Ru-C(1)-C(2) 171.8(8)°). The angle P(1)-Ru-
P(2) of 96.85(7)° is slightly higher than in the alkyne complex
1 (93.67(4)°) due to the lesser steric requirements of the
vinylidene. The IR spectrum of 3 exhibits a strong absorption
at 1611 cm-1. In the 1H NMR spectrum, the vinylidene protons
appear at 3.57 ppm as a phosphorus-coupled triplet (4JHP ) 1.8
Hz). The R carbon is found at 345.9 ppm as a triplet with 21.5
Hz of coupling constant, whereas the â carbon gives rise to a
singlet at 102.9 ppm in the 13C{1H} NMR.
The tautomerization process resembles to a great extent to
that observed for the activation of 1-alkynes by [Cp*RuCl-
(dippe)]:11,12 the isomerization rate depends on the alkyne
substituent, being R ) COOEt < Ph < SiMe3 < tBu (according
9
3314 J. AM. CHEM. SOC. VOL. 125, NO. 11, 2003

π-Alkyne, Alkynyl-Hydride, and Vinylidene Isomers
A R T I C L E S
Scheme 3
Figure 5. ORTEP drawing (50% thermal ellipsoids) of [Cp*Ru(dCd
CHCOOMe)(PEt3)2]+ (10).
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Compound 10 with Estimated Standard Deviations in Parentheses
bond distances (Å)
bond angles (deg)
10
to this, complex 8 has only been obtained as a minor product
besides its vinylidene isomer); these compounds rearrange
spontaneously in the solid state to vinylidene so that they must
be stored below room temperature. On the other hand, the
isomerization takes place slower in complexes with PEt3 than
in those with dippe, as it has been previously observed in the
interaction of [Cp*RuCl(PEt3)2] with alkynols.13
Ru(1)P(1)
Ru(1)P(2)
Ru(1)C(11)
C(11)C(12)
C(12)C(13)
2.360(2)
2.340(2)
1.806(8)
1.308(10)
1.450(12)
P(1)Ru(1)P(2)
92.15(8)
87.6(2)
92.4(2)
175.4(6)
123.3(8)
P(1)Ru(1)C(11)
P(2)Ru(1)C(11)
Ru(1)C(11)C(12)
C(11)C(12)C(13)
The X-ray determined structure of compound 2 shows a
transoid disposition of the alkynyl and hydride ligands with a
Calkynyl-Ru-Hhydride angle of 131.3(16)°. The computed value
of Calkynyl-Ru-Hhydride angle in complex 2A is 129.2°, very
close to the experimental one. Another alkynyl-hydride isomer
is still conceivable, that with the alkynyl and hydride ligands
in cisoid disposition. However, and despite the many efforts
made, it has not been possible to find such alkynyl-hydride
isomer. Instead, we located a stable minimum corresponding
to a η2-(C,H) coordination of the acetylene moiety to the metal.
The participation of such σ alkyne complex as intermediate in
the alkyne-vinylidene isomerization has been suggested in
several theoretical studies.2b,5a,b,6 It is noteworthy that in recent
theoretical works on analogous d6 half-sandwich systems,
[CpRu(PH3)2(C2HMe)]+7d and CpMn(CO)2(C2H2),2b only the
transoid alkynyl-hydride isomer was characterized as a mini-
mum, with Calkynyl-M-Hhydride angles of 122.9° and 132.5°,
respectively. Moreover, both studies found structures with
Calkynyl-M-Hhydride angles of 68.0° and 78.4° respectively,
corresponding to the transition states for the oxidative addition
from the alkyne to the alkynyl-hydride isomer.
Relevant geometric features of the X-ray data are compared
in Table 4 to the calculated results of the full ab initio model
[CpRu(C2H2)(PH3)2]+ (A), and the quantum mechanics/molec-
ular mechanics (QM/MM) model [Cp*Ru(C2H2)(PEt3)2]+ (B).
The calculated metal-carbon (Ru-CR) and carbon-carbon
(CR-Câ) distances in 1A, 2A, and 3A (2.252, 2.252 and 1.247
Å, 2.048 and 1.219 Å, and 1.871 and 1.306 Å, respectively)
agree well with the distances determined by X-ray diffraction
(2.182(4), 2.180(5) and 1.220(7) Å for 1, 2.034(4) and 1.150-
(6) Å for 2, 1.835(8) and 1.296(11) Å for 3), reflecting the
change of bond orders in the different isomers. On the other
hand, the computed values of the P-Ru-P angle (89.4°, 103.8°,
and 90.5° for 1A, 2A and 3A, respectively) are lower than those
obtained from the X-ray diffraction analysis (93.67(4)°,
The vinylidene complexes [Cp*Ru(dCdCHR)(PEt3)2][BPh4]
t
(R ) Ph (9), COOMe (10), Bu(11)) have been obtained by
stirring a solution of [Cp*RuCl(PEt3)2] and the corresponding
alkyne for 6 h in MeOH. The subsequent addition of NaBPh4
causes the precipitation of an orange microcrystalline solid. The
IR spectra show a strong and broad vinylidene absorption in
the range 1620-1700 cm-1. The vinylidene proton appears at
5.12, 4.70, and 3.72, respectively for compounds 9-11 in the
1H NMR spectra. The 13C{1H} NMR signal for the vinylidene
R carbon appears around 345 ppm. Recrystallization of 10 gave
orange crystals suitable for X-ray structural analysis. An ORTEP
view of the cationic complex is depicted in Figure 5. Selected
bond lengths and angles are listed in Table 3.
The distances Ru-C(11) (1.806(8) Å) and C(11)-C(12)
(1.308(10) Å) are quite similar to those observed for the primary
vinylidene complex 3 (1.835(8) Å and 1.296(11) Å). Likewise
the atoms Ru-C(11)-C(12) (175.4(6)°) are almost lineally
arranged. All angles around C(12) and C(13) are close to 120°,
in agreement with a sp2 hybridization.
Finally, the isomerization of the alkynyl-hydride complex 5
(R ) SiMe3) to vinylidene occurs followed by an immediate
desilylation process, leading directly to the formation of the
aforementioned primary vinylidene 3.
Theoretical Study
Structural Analysis. The theoretical study started by search-
ing equilibrium structures on the potential energy surface of
the [CpRu(C2H2)(PH3)2]+ (A) model system. We found three
minima 1A, 2A, and 3A, corresponding respectively, to the three
X-ray characterized complexes, i.e., the η2-acetylene complex
1, the alkynyl-hydride complex 2 and the η1-vinylidene complex
3. The geometries of model complexes 1A, 2A, and 3A were
fully optimized without any symmetry constrains, and their
natures as minima were confirmed by normal-mode analysis.
9
J. AM. CHEM. SOC. VOL. 125, NO. 11, 2003 3315

A R T I C L E S
Bustelo et al.
Table 4. Relevant Bond Lengths (Å) and Angles (deg) of the Calculated Structures of Simplified Model [CpRu(PH3)2(C2H2)]+ (A) and
QM/MM Model [Cp*Ru(PEt3)2(C2H2)]+ (B) Compared to X-ray Structural Data
π-alkyne
1A
alkynyl-hydride
2A
vinylidene
3A
1
1B
2
2B
3
3B
parameter
X-ray
full ab initio
QM/MM
X-ray
full ab initio
2.048
QM/MM
2.041
X-ray
full ab initio
1.871
QM/MM
1.863
Ru-CR
2.180(5)
2.182(4)
1.220(7)
93.67(4)
2.252
2.252
1.247
89.4
2.252
2.255
1.245
94.1
2.034(4)
1.835(8)
CR-Câ
P-Ru-P
1.150(6)
107.20(4)
1.219
103.8
1.219
105.5
1.296(11)
96.85(7)
1.306
90.5
1.308
96.2
Scheme 4
107.20(4)°, and 96.85(7)° for 1, 2 and 3, respectively). The
computed structure of complex 1A shows an orthogonal
arrangement of the acetylene unit with torsion angles Cp-Ru-
Mp-Calkyne (Cp, ring centroid; Mp, alkyne CtC midpoint) of
90.0° and -90.0°, whereas in the X-ray structure of 1 the torsion
angles are 69.3° and -110.7°.
It was described above that, in acetylene complex 1, the
rotational orientation of the acetylene unit relative to the
[Cp*Ru(PEt3)2]+ moiety deviates from its ideal perpendicular
arrangement. However, the optimization of compound [CpRu-
(PH3)2(HCtCH)]+ (1A) revealed a preference for perpendicular
disposition. To evaluate the energy cost of acetylene deviation
we performed a partial optimization, forcing the torsion angles
P-Ru-Calkyne-Calkyne to remain at the values of the crystal
structure. The resulting structure was found only 0.7 kcal‚mol-1
above the minimum 1A. This value gives an estimation of the
energy cost for acetylene distortion, indicating a very low energy
cost for the rotation of the acetylene from its idealized position
to that found in X-ray data. Furthermore, the computed energy
barrier for rotation of acetylene unit around the metal fragment
symmetry at the metal center and induces a distortion of the
acetylene unit in order to minimize the steric repulsion.
To further confirm our arguments we carried out additional
pure quantum mechanics calculations on two additional model
systems [Cp*Ru(C2H2)(PH3)2]+ (C), and [CpRu(C2H2)(PMe3)2]+
(D). In the case of alkyne complex 1C, where the Cp ligand
has been replaced by a Cp* but keeping the simple PH3
phosphines, no acetylene distortion was observed. On the other
hand, in complex 1D, where the simple PH3 phosphines were
replaced by the bulkier PMe3 phosphines but keeping the Cp
model ligand, the rotational orientation of acetylene deviates
from its ideal perpendicular disposition with torsion angles Cp-
Ru-Mp-Calkyne of 79.4° and -100.6°. Therefore, these results
support the fact that the steric effect induced by the bulky
phosphine substituents is responsible of the acetylene distortion.
is not high, 8.2 kcal‚mol-1
.
The lower values of P-Ru-P angles found for [CpRu(C2H2)-
(PH3)2]+ (A) indicate that the PH3 model phosphine does not
reproduce the steric hindrance induced by triethylphosphine
ligands, suggesting that this missing effect could be responsible
for discrepancies with experimental data in acetylene arrange-
ment. To analyze acetylene distortion, hybrid quantum mechan-
ics/molecular mechanics (QM/MM) with the IMOMM method18
were carried out on a more realistic system [Cp*Ru(C2H2)-
(PEt3)2]+ (B). The QM region was [CpRu(C2H2)(PH3)2]+,
whereas the MM region included the methyl and ethyl substit-
uents of Cp and phosphine, respectively. Note that this QM/
MM method accounts only for the steric properties of the atoms
included in the MM region. The inclusion of steric effects of
bulky ligands is reflected on an increase of the computed
P-Ru-P angle with respect to model A to values closer to the
experimental ones (Table 4). Now, the computed torsion angles
Cp-Ru-Mp-Calkyne are 74.0° and -106.0°, reproducing the
experimental observed acetylene distortion. Thus, the incorpora-
tion of the steric effects of bulky ligands distorts the rotational
orientation of acetylene in 1B, despite the electronic preference
for the perpendicular arrangement found in 1A.
Relative Energies of the Three Isomers. The calculated
relative energies of the three C2H2 isomers for A, B, C, and D
systems are summarized in Table 5. The vinylidene complex
3A is found as the global energy minimum structure, being 8.6
and 28.5 kcal‚mol-1 lower than the acetylene 1A and alkynyl-
hydride 2A complexes, respectively. Thus, the alkynyl-hydride
complex lays 19.9 kcal‚mol-1 above the acetylene complex.
Although predicting the vinylidene as the most stable isomer is
alike the experimental results, the high destabilization of alkynyl-
hydride with respect to the acetylene isomer does not seem to
agree with experimental observations.
Our DFT methodology has been successfully tested in a
previous study of alkyne-vinylidene isomerization on the
coordination sphere of niobocene complexes.5a The calculated
relative energy for the free vinylidene with respect to acetylene
at our computational level (41.8 kcal‚mol-1) reproduces previous
theoretical19 and experimental results.20 Furthermore, the result
for F4W system (alkyne isomer 8.1 kcal‚mol-1 more stable than
These findings may seem surprising since the metal fragment
[Cp*Ru(PEt3)2]+ possess in principle a symmetry molecular
plane containing the Ru atom, the Cp centroid and bisecting
the two phosphine ligands. However, a closer inspection of the
structure 1B revealed that the bulky substituents of the phosphine
ligand are alternate (Scheme 4). This configuration breaks the
(19) See, for example: (a) Gallo, M. M.; Hamilton, T. P.; Schaefer, H. F. J.
Am. Chem. Soc. 1990, 112, 8714. (b) Petersson, G. A.; Tensfeldt, T. G.;
Montgomery, J. A., Jr. J. Am. Chem. Soc. 1992, 114, 6133. (c) Jensen, J.
H.; Morokuma, K.; Gordon, M. S. J. Chem. Phys. 1994, 100, 1981.
(18) (a) Maseras, F.; Morokuma, K. J Comput Chem. 1995, 16, 1170. (b)
Maseras, F. Chem. Commun. 2000, 1821-1827.
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3316 J. AM. CHEM. SOC. VOL. 125, NO. 11, 2003

π-Alkyne, Alkynyl-Hydride, and Vinylidene Isomers
A R T I C L E S
Table 5. Calculated Relative Energies of the Three C2H2 Isomers for A, B, C and D Systems. Energies in kcal‚mol-1
CpRu(C H )
[Cp*Ru(C H )
[Cp*Ru(C H )
[[Cp*Ru(C H )
[CpRu(C H )
2
2
2
2
2
2
2
2
2
2
(PH ) ]+
(PEt3)2]+
(PEt3)2]+
(PH ) ]+
(PMe3)2]+
3 2
3 2
isomer
QM (A)
QM/MM (B)
QM//QM/MM (B)
QM(C)
QM(D)
acetylene
alkynyl-hydride
vinylidene
+8.6
+28.5
0.0
+15.7
+27.6
0.0
+16.3
+19.6
0.0
+8.2
+25.0
0.0
+12.4
+23.1
0.0
vinylidene) is also in agreement with previously reported value
at the CCSD(T)//DFT level (10.4 kcal‚mol-1).5b
of the ligands substituents in the relative stabilities of the three
C2H2 isomers, we performed full ab initio energy calculations
on the optimized QM/MM geometries of model [Cp*Ru(C2H2)-
(PEt3)2]+ (B). Taking as the zero of energy the vinylidene
species, the energies of the acetylene and the alkynyl-hydride
isomers are +16.3 and +19.6 kcal‚mol-1, respectively. The
comparison of the relative energies with those obtained in QM/
MM calculation on B, shows a substantial energy lowering of
the alkynyl-hydride isomer (8.0 kcal‚mol-1, from 27.6 to 19.6
kcal‚mol-1) and small energy variation of the acetylene isomer
(from 15.7 to 16.3 kcal‚mol-1), in marked contrast with that
found on going from model A to B. The most striking result is
that relative energies of the acetylene and alkynyl-hydride
isomers became very similar (3.3 kcal‚mol-1), in better agree-
ment with the experimental results because both isomers could
be prepared. The energy differences between the two forms that
were found are within the limits of accuracy of the modeling
and the methodology employed, but a definitive answer with
regard to which is the most stable species cannot be established.
To the best of our knowledge this is the first time that QM/
MM methods have been used this way, i.e., combined with full
ab initio energy calculation. The success in reproducing
experimental trends suggests that this procedure could be useful
when the electronic ligand effects are important to model
experimental complexity, expanding the range of applications
of these methods.
In summary, the sequential refinement of the model system
has allowed separating, identifying and evaluating different
contributions of the ligands to the thermodynamics of the
system. The sequence is schematically depicted in Figure 6.
First, upon introduction of steric effects of bulky ligand
substituents, is observed a relative destabilization of the alkyne
form, while the relative energy of alkynyl-hydride complex
remains almost unchanged. Second, recovering the electronic
effects of the donor substituents causes a stabilization of the
alkynyl-hydride form with respect to the alkyne and the
vinylidene. The combination of these two effects makes alkyne
and alkynyl-hydride complexes to be very close in energy,
allowing the isolation of the unusual ruthenium alkynyl-hydride
complex.
It is worth comparing the thermodynamics of the system with
those reported in previous theoretical works for analogous
d6 metal systems: Ru(II) [Cl2Ru(PH3)2(C2H2)],7a [CpRu(PH3)2-
(C2HMe)]+,7d Mn(I) [CpMn(CO)2(C2H2)],2b and Os(II) [CpOs-
(PH3)2(C2H2)]+.8e In all cases, the vinylidene isomer is predicted
to be the most stable one, whereas the alkynyl-hydride isomer
is the highest in energy. These thermodynamic trends are in
the line with those computed for our model system [CpRu-
(C2H2)(PH3)2]+ (A). In fact, it has been proposed7a,10d that for
d6 systems the oxidative addition of the alkyne to the alkynyl-
hydride complexes is difficult since the metal changes from d6
to d4. However, this is not the case of the metal system under
investigation, in which the acetylene complex 1 isomerizes
spontaneously to the corresponding alkynyl-hydride complex
2.
Up till now, theoretical studies have only been performed
on simplified model systems. Here, we have carried out QM/
MM calculations on the real system [Cp*Ru(C2H2)(PEt3)2]+ (B),
because it seems that the simplified models do not account for
the experimental complexity. The results show that the acetylene
isomer 1B and the alkynyl-hydride 2B are respectively, 15.7
and 27.6 kcal‚mol-1 higher in energy than the vinylidene isomer
3B. On going from model A to B, i.e., including the steric effects
of ligand substituents, we observed that the acetylene isomer is
destabilized with respect to the vinylidene in 7.1 kcal‚mol-1
(from 8.6 to 15.7 kcal‚mol-1), whereas the relative stability of
the alkynyl-hydride isomer remains practically unchanged (from
28.5 to 27.6 kcal‚mol-1). This also implies a significant
reduction of the energy difference between the acetylene and
the alkynyl-hydride complexes, from 19.9 to 11.9 kcal‚mol-1
.
During the last years the hybrid QM/MM methods have
emerged as a powerful tool in the study of organometallic
compounds. The IMOMM and related methods have been
successfully applied to a range of problems such as homoge-
neous catalysis21 or structural issues associated with steric
effects.22 However, in these methods the electronic contributions
of the MM atoms are left out. To evaluate the electronic effects
(20) (a) Ervin, K. M.; Ho, J.; Lineberger, W. C. J. Chem. Phys. 1989, 91, 5974.
(b) Ervin, K. M.; Gronert, S.; Barlow, S. E.; Gilles, M. K.; Harrison, A.
G.; Bierbaum, V. M.; De Puy, C. H.; Lineberger, W. C.; Ellison, G. B. J.
Am. Chem. Soc. 1990, 112, 5750. (c) Chen, Y.; Jonas, D. M.; Hamilton,
C. E.; Green, P. G.; Kinsey, J. L.; Field, R. W. Ber. Bunsen-Ges. Phys.
Chem. 1988, 92, 329. (d) Chen, Y.; Jonas, D. M.; Kinsey, J. L.; Field, R.
W. J. Chem. Phys. 1989, 91, 3976.
(21) For some recent references, see: (a) Ujaque, G.; Maseras, F.; Lledo´s, A.
J. Am. Chem. Soc. 1999, 121, 1317. (b) Va´zquez, J.; Perica`s, M. A.;
Maseras, F.; Lledo´s, A. J. Org. Chem. 2000, 65, 7303. (c) Carbo´, J. J.;
Maseras, F.; Bo, C.; van Leeuwen, P. W. N. M. J. Am. Chem. Soc. 2001,
123, 7630-7637. (d) Feldgus, S.; Landis, C. R. J. Am. Chem. Soc. 2000,
122, 12714. (e) Feldgus, S.; Landis, C. R. Organometallics 2001, 20, 2374.
(f) Goldfuss, B.; Steigelmann, M.; Khan, S. I.; Houk, K. N. J. Org. Chem.
2000, 65, 77. (g) Cavallo, L.; Sola`, M. J. Am. Chem. Soc. 2001, 123, 12 294.
(h) Milano, G.; Guerra, G.; Pellecchia, C.; Cavallo, L. Organometallics
2000, 19, 1343. (i) Musaev, D. G.; Froese, R. D. J.; Morokuma, K.
Organometallics 1998, 17, 1850.
To analyze in more detail the contributions of the different
ligands to thermodynamics, pure quantum mechanics calcula-
tions have been carried out on [(C5Me5)Ru(C2H2)(PH3)2]+ (C)
and [CpRu(C2H2)(PMe3)2]+ (D) model systems. The replace-
ment of the Cp ligand (model A) by the better π donor Cp*
ligand (model C) stabilizes the alkynyl-hydride isomer with
respect to vinylidene in about 4 kcal‚mol-1, whereas the relative
energy of the acetylene isomer remains very similar (from 8.6
to 8.2 kcal‚mol-1). Moreover, the presence of the bulkier and
(22) (a) Barea, G.; Lledo´s, A.; Maseras, F.; Jean, Y. Inorg. Chem. 1998, 37,
3321. (b) Ujaque, G.; Cooper, A. C.; Maseras, F.; Eisenstein, O.; Caulton,
K. G. J. Am. Chem. Soc. 1998, 120, 361.
9
J. AM. CHEM. SOC. VOL. 125, NO. 11, 2003 3317

A R T I C L E S
Bustelo et al.
Figure 6. Schematic representation of the evolution of the relative energies of the three C2H2 isomers upon successive introduction of steric effects (QM/
MM (A)) and electronic effects (QM//QM/MM (B)).
more basic PMe3 phosphines in model D instead of the PH3
used in model A led to a higher destabilization of the alkyne
species (from 8.6 to 12.4 kcal‚mol-1) and to the stabilization
of the alkynyl-hydride species (from 28.5 to 23.1 kcal‚mol-1).
The destabilization of the alkyne isomer is due to the greater
steric hindrance of PMe3 phosphines, whereas the stabilization
of alkynyl-hydride isomer is due to the higher basicity with
respect to PH3 phosphine. Up until now, the discussion has been
done on the basis of the relative energies of the different isomers
with respect to vinylidene species. To gain insight into the
overall energetics of the phosphine exchange we make use of
ligand-transfer reactions
with the acetylene isomer using high-level computational
methods (as CCSD(T)) able to represent better back-bonding.
Unfortunately such calculations are not feasible at the present
time, and a definitive answer about which is the most stable
species cannot be done at this time.
Conclusions
In the present paper, we have reported new experimental data
and theoretical support on the alkyne/vinylidene isomerization,
which has been during the past decades a permanent subject of
research on the field of the organometallic chemistry. The X-ray
structures of the three isomers involved in the activation of
acetylene by a particular transition metal complex have been
determined for the first time. The isolation and structural
characterization of the three isomers provides a sound experi-
mental proof of the existence and accesibility of such species.
In general, π-alkyne, alkynyl-hydride, and vinylidene isomers
are species mutually exclusive due to their opposed thermody-
namic stabilities, but they have been frequently proposed as the
necessary intermediates in the way to vinylidenes. Moreover,
in the chemistry of ruthenium the isomerization to vinylidene
via 1,2-H shift from the π-alkyne has an experimental and
theoretical support as the most feasible explanation for the
tautomerization process. The alternative pathway via alkynyl-
hydride intermediates has been proven to be accessible by
[Cp*Ru(P)2]+ systems (P2 ) dippe, 2 PEt3), which exhibit a
remarkable different behavior. Additionally, we have used the
structural data obtained from the X-ray difraction analysis as
the starting point to carry out theoretical studies on this system.
These studies have separated and identified the reasons that
explain the observed behavior on the basis of the electronic and
steric effects induced by the auxiliary ligands. On the other hand,
the ability of theoretical methods to predict molecular features
has been tested against a number of experimental facts observed
in our particular system. This comparison has led to a sequential
refinement of the model system, allowing to separate, identify,
and evaluate the different contributions to the thermodynamics
of the system. Thus, the bulkiness of phosphine ligand induces
alkyne distortion and relative destabilization of alkyne isomer,
whereas the donor capabilities of the auxiliary ligands are
responsible of relative stabilization of vinylidene isomer. The
combination of these two effects is behind the reason the three
C2H2 isomers have been isolated in this particular system.
[CpRu(HCtCH)(PH3)2]+ + 2PMe3 f
[CpRu(HCtCH)(PMe3)2]+ + 2PH3
[CpRuH(CCH)(PH3)2]+ + 2PMe3 f
[CpRuH(CCH)(PMe3)2]+ + 2PH3
[CpRu(CdCH2)(PH3)2]+ + 2PMe3 f
[CpRu(CdCH2)(PMe3)2]+ + 2PH3
This kind of scheme provides a measure of the stability change
caused by the replacement of phosphine ligands for a given
isomer. The energy change for the ligand-transfer reaction of
acetylene, alkynyl-hydride and vinylidene isomers are, respec-
tively, +1.6, -8.0, and -2.4 kcal‚mol-1. For alkynyl-hydride
and vinylidene the reaction is exothermic, indicating the
preference for basic phosphines, especially in the case of
alkynyl-hydride. On the other hand, for acetylene isomer the
reaction is endothermic, indicating that the use of bulkier
phosphines destabilizes the complex. Finally, we can conclude
that bulky phosphine ligands work against the most steric
hindered isomer, the acetylene, whereas the use of basic
phosphines and σ donor ligands makes more electron rich the
metal center, favoring the obtaining of the alkynyl-hydride
isomer.
It is clear from our results, particularly from the energies of
the ligand exchange reactions that the hydride-alkynyl isomer
is especially sensitive to back-donation effects. Back-bonding
could be slightly underestimated in DFT calculations, and the
hydrido-alkynyl isomer could become even more competitive
9
3318 J. AM. CHEM. SOC. VOL. 125, NO. 11, 2003

π-Alkyne, Alkynyl-Hydride, and Vinylidene Isomers
A R T I C L E S
2 in a CH2Cl2 solution, which takes places at temperatures over 10 °C.
This procedure requires a careful temperature control to avoid side-
reactions, which occur above 20 °C. In these conditions, although the
yielding is almost quantitative, the process is rather slow.
Furthermore, we proved that small changes in auxiliary ligands
have a dramatic influence in the relative energies of the different
isomers, so caution should be taken when modeling these
systems. The novel application of QM/MM methods combined
with full ab initio energy calculation, and the success in
reproducing experimental trends, allow to propose the potential
utility of this procedure in situations where a particular
configuration of ligands around a metal induces unusual
properties or exhibits a comparatively different behavior.
Method B. A solution of 1 (300 mg, 0.36 mmol) in THF (5 mL)
t
was treated with an excess of BuOK (114 mg, 95%, 1.0 mmol). The
mixture was stirred for 15 min at room temperature, and then taken to
dryness. The residue extracted with petroleum ether (2 × 5 mL). The
yellow solution was then filtered through diatomaceous earth and the
solvent removed under vacuum, affording a yellow microcrystalline
solid corresponding to the neutral alkynyl complex 4. Microanalysis
and selected spectral data for complex 4 are reported below. A solution
of 4 in Et2O (3 mL) was cooled in an ethanol/liquid N2 bath, and treated
with 10 µL of HBF4 (85% solution of HBF4‚Et2O). An orange solid
was immediately formed. The bath was removed and the mixture was
allowed to reach room temperature. The solid was separated by
decantation, washed twice with Et2O (3 mL) and dried in vacuo,
corresponding to the vinylidene complex 3 as a BF4 salt. Yield: 144
mg (68.3% from 1).
Experimental Section
All synthetic operations were performed under a dry dinitrogen or
argon atmosphere by following conventional Schlenk techniques.
Tetrahydrofuran, diethyl ether and petroleum ether (boiling point range,
40-60 °C) were distilled from the appropriate drying agents. All
solvents were deoxygenated immediately before use. IR spectra were
recorded in Nujol mulls on a Perkin-Elmer FTIR Spectrum 1000
spectrophotometer. NMR spectra were taken on a Varian Unity 400
MHz or Varian Gemini 200 MHz equipment. Chemical shifts are given
in parts per million from SiMe4 (1H and 13C{1H}) or 85% H3PO4 (31P-
{1H}). NMR data of the [BPh4]- ion appeared in the appropriate shift
ranges for cationic compounds isolated as its salts and are omitted for
clarity. Microanalysis was performed by the Serveis Cient´ıfico-Te`cnics,
Universitat of Barcelona.
Preparation of the Alkyne Complex [Cp*Ru(η2-HCtCH)(PEt3)2]-
[BPh4] (1). Acetylene gas was bubbled through a solution of NaBPh4
(194 mg, 1.2 mmol) in 10 mL of methanol. The addition of [Cp*RuCl-
(PEt3)2] (508 mg, 1 mmol) caused the immediate precipitation of a
yellow solid, which was filtered, washed with ethanol and petroleum
ether, dried under vacuum and stored at -20 °C. Yield: 695 mg (85%).
This compound was recrystallized from an ethanol/acetone mixture (3:
1) at -20 °C, yielding a mixture of yellow crystals corresponding to
1 (minor) and 2 (major). Microanalysis and selected spectral data are
as follows.
Method C. A solution of [Cp*RuCl(PEt3)2] (508 mg, 1 mmol) and
trimethylsilylacetylene (170 µL, 1.2 mmol) in MeOH (10 mL) was
stirred for 24 h at room temperature. Addition of NaBPh4 (194 mg,
1.2 mmol) caused the immediate precipitation of an orange solid, which
was separated by filtration and washed with EtOH and petroleum ether.
Recrystallization from CH2Cl2/petroleum ether (1:2) yielded orange
crystals suitable for X-ray structural analysis. Yield: 736 mg (90%).
(3). Anal. Calcd for C48H67BP2Ru: C, 70.5; H, 8.26. Found: C, 70.5;
H, 8.26. IR (Nujol): ν(CdC) 1611, ν(BPh4) 1580 cm-1. 1H NMR (400
MHz, CDCl3, 298 K): δ 1.00 (m, 18 H, PCH2CH3), 1.78 (s, C5(CH3)5),
4
1.62 and 1.84 (m, 12 H, PCH2CH3), 3.57 (t, 2 H, JHP ) 1.8 Hz, Cd
CH2). 31P{1H} NMR (161.9 MHz, CDCl3, 298 K): δ 31.7 (s). 13C-
{1H} NMR (100.6 MHz, CDCl3, 298 K): δ 8.86 (s, PCH2CH3), 10.84
(s, C5(CH3)5), 21.19 (m, PCH2CH3), 93.77 (s, C5(CH3)5), 102.9 (s, Câ),
2
345.9 (t, JCP ) 21.5 Hz, CR).
Preparation of the Neutral Ethynyl Complex [Cp*Ru(CtCH)-
(PEt3)2] (4). This compound has been obtained and characterized in
the two steps synthesis of the vinylidene complex 3, as it was described
above. Yield: 167 mg (93%). Microanalysis and selected spectral data
are as follows.
(1). Anal. Calcd for C48H67BP2Ru: C, 70.5; H, 8.26. Found: C, 70.5;
1
H, 8.25. IR (Nujol): ν(η2-CtC) 1732, ν(BPh4) 1580 cm-1. H NMR
(400 MHz, CDCl3, 253 K): δ 1.07 (m, 18 H, PCH2CH3), 1.53 (s, 15
3
H, C5(CH3)5), 1.69 (m, 12 H, PCH2CH3), 4.38 (t, 2 H, JHP ) 6.3 Hz,
(4). Anal. Calcd for C24H46P2Ru: C, 57.9; H, 9.32. Found: C, 57.8;
C2H2). 31P{1H} NMR (161.9 MHz, CDCl3, 253 K): δ 23.82 (s). 13C-
{1H} NMR (100.6 MHz, CDCl3, 253 K): δ 9.11 (s, PCH2CH3), 10.21
1
H, 9.30. IR (Nujol): ν(CtC) 1942 cm-1. H NMR (400 MHz, C6D6,
298 K): δ 1.02 (m, 18 H, PCH2CH3), 1.74 (s, 15 H, C5(CH3)5), 1.57
(s, C5(CH3)5), 19.83 (vt, 1,3JCP ) 13.7 Hz, PCH2CH3), 66.14 (t, 2JCP
3.5 Hz, C2H2), 96.90 (s, C5(CH3)5).
)
4
and 1.81 (m, 12 H, PCH2CH3), 2.05 (t, 1 H, JHP ) 2.2 Hz, CtCH).
31P{1H} NMR (161.9 MHz, C6D6, 298 K): δ 32.4 (s). 13C{1H} NMR
Preparation of the Alkynyl-Hydride Complex [Cp*Ru(H)(CtCH)-
(PEt3)2][BPh4] (2). A solution of complex 1 (150 mg, 0.18 mmol) in
5 mL of CH2Cl2 was kept at -20 °C for 72 h, undergoing spontaneous
and irreversible isomerization to the alkynyl-hydride isomer 2. The
solvent was removed under vacuum and a pale yellow solid was
obtained in quantitative yield. This compound must be stored below
room temperature to prevent isomerization to vinylidene. Suitable
crystals for XRD analysis were obtained from the recrystallization of
the parent alkyne complex 1. Microanalysis and selected spectral data
are as follows.
(100.6 MHz, C6D6, 298 K): δ 9.00 (s, PCH2CH3), 11.25 (s, C5(CH3)5),
1,3
22.00 (vt,
J
) 11.5 Hz, PCH2CH3), 91.29 (s, Câ), 92.22 (s, C5-
CP
2
(CH3)5), 108.9 (t, JCP ) 25.9 Hz, CR).
Preparation of the Alkynyl-Hydride Complexes [Cp*Ru(H)-
(CtCR)(PEt3)2][BPh4] (R ) SiMe3 (5), Ph (6), COOMe (7),
tBu(8)). To a solution of the corresponding alkyne (0.40 mmol) and
NaBPh4 (81 mg, 0.50 mmol) in 10 mL of MeOH at 0 °C (ice bath),
were added 127 mg (0.25 mmol) of [Cp*RuCl(PEt3)2]. The bath was
removed and the mixture allowed to warm until a white microcrystalline
solid precipitated. This solid was immediately filtered, washed with
cold ethanol and petroleum ether, and dried under vacuum. Complexes
5, 6, and 8 were stored at 0 °C to prevent the isomerization to
vinylidene.
(2). Anal. Calcd for C48H67BP2Ru: C, 70.5; H, 8.26. Found: C, 70.5;
H, 8.25. IR (Nujol): ν(CtC) 1965, ν(Ru-H) 1935, ν(BPh4) 1580 cm-1
.
2
1H NMR (400 MHz, CDCl3, 278 K): δ - 9.27 (t, 1 H, JHP ) 29.5
Hz, Ru-H), 1.11 (m, 18 H, PCH2CH3), 1.70 (s, 15 H, C5(CH3)5), 1.82
(5). Yield: 175 mg (79%). Anal. Calcd for C51H75BP2RuSi: C,
68.8; H, 8.49. Found: C, 69.0; H, 8.50. IR (Nujol): ν(CtC) 2039,
4
(m, 12 H, PCH2CH3), 2.09 (t, 1 H, JHP ) 2.7 Hz, CtCH). 31P{1H}
NMR (161.9 MHz, CDCl3, 278 K): δ 37.7 (s). 13C{1H} NMR (100.6
1
ν(Ru-H) 2142 cm-1. H NMR (400 MHz, CDCl3, 253 K): δ -9.20
3,5
2
MHz, CDCl3, 278 K): δ 8.90 (vt,
J
) 3.0 Hz, PCH2CH3), 10.07
HP
(t, 1 H, JHP ) 27.0 Hz, Ru-H), 0.18 (s, 9 H, Si(CH3)3), 1.08 (m, 18
(s, C5(CH3)5), 20.14 (m, PCH2CH3), 93.09 (t, 2JCP ) 29 Hz, CR), 101.4
(s, C5(CH3)5), 102.1 (s, Câ).
H, PCH2CH3), 1.75 (s, 15 H, C5(CH3)5), 1.81 (m, 12 H, PCH2CH3).
31P{1H} NMR (161.9 MHz, CDCl3, 253 K): δ 37.6 (s). 13C{1H} NMR
(100.6 MHz, CDCl3, 253 K): δ 0.82 (s, Si(CH3)3), 8.95 (s, PCH2CH3),
10.00 (s, C5(CH3)5), 20.02 (m, PCH2CH3), 101.7 (s, C5(CH3)5), 106.1
(s, CR), 121.9 (s, Câ).
Preparation of the Vinylidene Complex [Cp*Ru(dCdCH2)-
(PEt3)2][X] (3). Method A. Complex 3 was initially obtained as BPh4
salt by the spontaneous isomerization of the ethynyl-hydride precursor
9
J. AM. CHEM. SOC. VOL. 125, NO. 11, 2003 3319

A R T I C L E S
Bustelo et al.
Table 6. Summary of Crystallographic Data for Compounds 1-3 and 10
compd
1
2
3
10
formula
FW
C48H67BP2Ru
817.84
C48H67BP2Ru
817.84
C48H67BP2Ru
817.84
C50H69BO2P2Ru
875.87
T (K)
183(2)
183(2)
293(2)
293(2)
crystal color
crystal system
space group
yellow, prism
monoclinic
P2(1)/c
a ) 10.424(3) Å
b ) 21.503(6) Å
c ) 19.484(5) Å
R ) γ ) 90°
â ) 94.67(1)°
4
yellow, prism
orthorombic
P2(1)2(1)2(1)
a ) 13.604(2) Å
b ) 16.518(3) Å
c ) 19.219(3) Å
R ) â ) γ ) 90°
yellow, plate
orthorombic
P2(1)2(1)2(1)
a ) 13.5677(7)
b ) 17.2811(8)
c ) 19.0256(9)
R ) â ) γ ) 90°
yellow, prism
monoclinic
P2(1)/n
a ) 16.367(3) Å
b ) 16.006(5) Å
c ) 17.669(3) Å
R ) γ ) 90°
â ) 95.13(2)°
4
cell parameters
Z
4
4
final R1,a wR2b values (I > 2σI)
final R1,a wR2bvalues (all data)
GOF
0.0477, 0.1211
0.0635, 0.1325
1.070
0.0432, 0.1046
0.0520, 0.1115
1.091
0.0640, 0.1314
0.0678, 0.1333
1.034
0.0586, 0.1529
0.1216, 0.1806
1.081
2
2
2
a R1 ) ∑{[Fo] - [Fc]}/∑[Fo]. b wR2 ) [∑{w(Fo - Fc )2}/∑{w(Fo )2}]1/2
.
(6). Yield: 185 mg (83%). Anal. Calcd for C54H71BP2Ru: C, 72.6;
H, 8.01. Found: C, 72.8.0; H, 7.99. IR (Nujol): ν(CtC) 2105, ν(Ru-
MHz, CDCl3, 298 K): δ 28.45 (s). 13C{1H} NMR (100.6 MHz, CDCl3,
298 K): 8.81 (s, PCH2CH3), 10.79 (s, C5(CH3)5), 20.60 (m, PCH2-
CH3), 51.47 (s, COOCH3), 104.5 (s, C5(CH3)5), 107.6 (s, Câ), 165.6
1
H) 2016, ν(Ph) 1592 cm-1. H NMR (400 MHz, CDCl3, 273 K): δ
-9.17 (t, 1 H, 2JHP ) 29.6 Hz, Ru-H), 1.12 (m, 18 H, PCH2CH3), 1.71
(s, 15 H, C5(CH3)5), 1.83 (m, 12 H, PCH2CH3), 7.20 and 7.26 (m, 5 H,
C6H5). 31P{1H} NMR (161.9 MHz, CDCl3, 273 K): δ 37.55 (s). 13C-
{1H} NMR (100.6 MHz, CDCl3, 273 K): 8.80 (s, PCH2CH3), 10.17
(s, C5(CH3)5), 20.18 (m, PCH2CH3), 104.0 (t, 2JCP ) 30 Hz, CR), 102.7
(s, C5(CH3)5), 112.0 (s, Câ), 124.4, 126.8, 127.0, and 143.2 (s, C6H5).
(7). Yield: 193 mg (88%). Anal. Calcd for C50H69BO2P2Ru: C, 68.6;
H, 7.94. Found: C, 69.0; H, 7.93. IR (Nujol): ν(CtC) 2109, ν(Ru-
H) 2013, ν(CO) 1693 cm-1. 1H NMR (400 MHz, CDCl3, 273 K): δ -
9.02 (t, 1 H, 2JHP ) 27.5 Hz, Ru-H), 1.10 (m, 18 H, PCH2CH3), 1.65
(s, 15 H, C5(CH3)5), 1.77 (m, 12 H, PCH2CH3), 3.67 (s, COOCH3).
31P{1H} NMR (161.9 MHz, CDCl3, 273 K): δ 37.54 (s). 13C{1H} NMR
(100.6 MHz, CDCl3, 273 K): δ 8.75 (s, PCH2CH3), 10.06 (s, C5(CH3)5),
20.18 (m, PCH2CH3), 52.07 (s, COOCH3), 102.4 (s, C5(CH3)5), 108.8
(s, COOCH3), 343.4 (t, JCP ) 15.0 Hz, CR).
2
(11). Yield: 186 mg (85%). Anal. Calcd for C52H75BP2Ru: C, 71.5;
H, 8.65. Found: C, 71.8; H, 8.60. IR (Nujol): ν(CdC) 1666 cm-1. 1H
NMR (400 MHz, CDCl3, 298 K): δ 1.03 (m, 18 H, PCH2CH3), 1.12
(s, 9 H, C(CH3)3), 1.74 (s, 15 H, C5(CH3)5), 1.69 and 1.82 (m, 12 H,
PCH2CH3), 3.72 (s, dCdCH). 31P{1H} NMR (161.9 MHz, CDCl3, 298
K): δ 27.94 (s). 13C{1H} NMR (100.6 MHz, CDCl3, 298 K): δ 9.21
(s, C(CH3)3), 10.17 (s, PCH2CH3), 11.03 (s, C5(CH3)5), 21.06 (m, PCH2-
CH3), 32.05 (s, C(CH3)3), 102.3 (s, C5(CH3)5), 106.4 (s, Câ), 347.1 (t,
2JCP ) 14.7 Hz, CR).
X-ray Structure Determinations. Suitable crystals of compounds
1-3 and 10 were used for X-ray crystal structure analysis. Crystal data
and experimental details are given in Table 6. Further details are given
in the Supporting Information. X-ray data of 1 and 2 were collected
on a Bruker AXS Smart CCD area detector diffractometer (graphite
monochromated MoKR radiation, λ ) 0.710 73 Å, 0.3° ω-scan frames
covering complete spheres of the reciprocal space), at the Institute of
Chemical Technologies and Analytics, Vienna University of Technol-
ogy. X-ray data of 3 were collected on a Bruker Smart Apex CCD
area detector diffractometer (graphite-monochromated MoKR radiation,
λ ) 0.710 73 Å, 0.3° ω-scan frames covering hemispheres of the
reciprocal space). X-ray data of 10 were collected on a MSC-Rigaku
AFC6S four-circle difractometer (graphite-monochromated MoKR
radiation, λ ) 0710 73 Å, ω/2θ scan method). Crystals 3 and 10 were
measured at the Servicio Central de Ciencia y Tecnolog´ıa de la
Universidad de Ca´diz.
3
2
(t, JCP ) 4.1 Hz, Câ), 112.2 (t, JCP ) 28.8 Hz, CR), 183.4 (s,
COOCH3).
(8). This compound is obtained as a minor product besides the
vinylidene isomer 11, and only some of the spectral data have been
identified: IR (Nujol): ν(CtC) 2143, ν(Ru-H) 2042 cm-1. 1H NMR
2
(400 MHz, CDCl3, 273 K): - 9.43 (t, 1 H, JHP ) 30.7 Hz, Ru-H).
31P{1H} NMR (161.9 MHz, CDCl3, 273 K): 36.73 (s).
Preparation of the Vinylidene Complexes [Cp*Ru(dCdCHR)-
t
(PEt3)2][BPh4] (R ) Ph (9), COOMe (10), Bu(11)). 127 mg (0.25
mmol) of [Cp*RuCl(PEt3)2] were dissolved in 10 mL of MeOH. An
excess of the corresponding 1-alkyne (0.40 mmol) was added and the
solution was stirred for 6 h. NaBPh4 (81 mg, 0.50 mmol) was added
and an orange solid precipitated immediately. This solid was filtered,
washed with EtOH and petroleum ether and dried under vacuum.
Recrystallization of compound 10 from an acetone/ethanol solution (1:
4), gave orange crystals suitable for X-ray structural analysis.
(9). Yield: 179 mg (80%). Anal. Calcd for C54H71BP2Ru: C, 72.6;
H, 8.01. Found: C, 72.8; H, 7.99. IR (Nujol): ν(CdC) 1621, ν(Ph)
In all the cases, corrections for Lorentz and polarization effects, for
crystal decay, and for absorption were applied. All structures were
solved using the program SHELXS97.23 Structure refinements on F2
were carried out with the program SHELXL97.24 For compounds 1, 3,
and 10, all non-hydrogen atoms were anisotropically refined. Hydrogen
atoms were refined in idealized positions riding with the atoms to which
they were bonded. For compound 2, two significant residual electron
densities, labeled Ru(1′) and P(2′), near Ru and P(2) were included in
the refinement allowing to vary x, y, z, population and Uiso parameters.
They are considered result of the presence of some 5% of the other
isomer dihapto-alkyne. All other non-hydrogen atoms were anisotro-
pically refined. Hydride hydrogen H(1) was refined unrestrained in x,
y, z, and Uiso. All other hydrogen atoms were refined in idealized
positions riding with the atoms to which they were bonded.
1
1592 cm-1. H NMR (400 MHz, CDCl3, 298 K): δ 1.01 (m, 18 H,
PCH2CH3), 1.79 (s, 15 H, C5(CH3)5), 1.71 and 1.83 (m, 12 H, PCH2-
CH3), 5.12 (s, dCdCH), 7.12 and 7.27 (m, 5 H, C6H5). 31P{1H} NMR
(161.9 MHz, CDCl3, 298 K): δ 27.84 (s). 13C{1H} NMR (100.6 MHz,
CDCl3, 298 K): δ 13.41 (s, PCH2CH3), 11.45 (s, C5(CH3)5), 22.84 (vt,
1,3
J
CP
) 13.8 Hz, PCH2CH3), 102.5 (s, C5(CH3)5), 113.4 (s, Câ), 124.7,
2
127.0 and 145.3 (s, C6H5), 342.8 (t, JCP ) 19.0 Hz, CR).
(10). Yield: 191 mg (87%). Anal. Calcd for C50H69BO2P2Ru: C,
68.6; H, 7.94. Found: C, 69.0; H, 7.93. IR (Nujol): ν(CdC) and ν(CO)
1694 cm-1. 1H NMR (400 MHz, CDCl3, 298 K): δ 1.01 and 1.17 (m,
18 H, PCH2CH3), 1.74 (s, 15 H, C5(CH3)5), 1.71 and 1.83 (m, 12 H,
PCH2CH3), 3.65 (s, COOCH3), 4.70 (s, dCdCH). 31P{1H} NMR (161.9
(23) Sheldrick, G. M. SHELXS97, Program for Crystal Structure Solution;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(24) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refinement;
University of Go¨ttingen, Go¨ttingen: Germany, 1997.
9
3320 J. AM. CHEM. SOC. VOL. 125, NO. 11, 2003

π-Alkyne, Alkynyl-Hydride, and Vinylidene Isomers
A R T I C L E S
Computational Details. Pure quantum mechanics calculations on
[CpRu(C2H2)(PH3)2]+ (A), [Cp*Ru(C2H2) (PH3)2]+ (C) and [CpRu-
(C2H2)(PMe3)2]+ (D) model systems were performed with the GAUSS-
IAN 98 series of programs25 within the framework of the Density
Functional Theory (DFT)26 using the B3LYP functional.27 A quasi-
relativistic effective core potential operator was used to represent the
28 innermost electrons of the Ru atom, as well as the 10 innermost
electrons of the P atom.28 The basis set for Ru and P atoms was that
associated with the pseudopotential,28 with a standard double-ê
LANL2DZ contraction,25 and in the case of P was supplemented by a
d shell.29
The 6-31G(d,p) basis set was used for the C2H2 unit and the C atoms
directly attached to the metal, whereas the 6-31G basis set was used
for the other carbon and hydrogen atoms.30 Geometry optimizations
were carried out without any symmetry restrictions and all stationary
points were optimized with analytical first derivatives. In the case of
model complex A, the local minima corresponding to the three C2H2
isomers were identified by the absence of negative eigenvalues in the
vibrational frequency analysis. The saddle point corresponding to
acetylene rotation in 1A was located by means of approximate Hessians
and synchronous transit-guided quasi-Newtonian methods.31
Hybrid QM/MM calculations with the IMOMM method18 were
carried out on [Cp*Ru(C2H2)(PEt3)2]+ (B) real system with a program
built from modified versions of the two standard programs GAUSSIAN
9823 for quantum mechanics part and MM3(92)32 for the molecular
mechanics part. The QM region was [(C5H5)Ru(C2H2)(PH3)2]+, whereas
the methyl and ethyl substituents of the cyclopentadienyl and phosphine
ligands were in the MM region. The quantum mechanics calculations
were done with the use of the same method and basis set described
above for the pure quantum mechanics calculations. Molecular mechan-
ics calculations used the MM3(92) force field.32 Default parameters
were used when available otherwise those of similar atoms replaced
the missing ones. The van der Waals parameters for the Ru atom were
taken from the UFF force field,33 and torsional contributions involving
dihedral angles with the metal atom in terminal position were set to
zero. All the geometrical parameters were optimized except for the
P-H (1.42 Å) and C(Cp)-H (1.101 Å) bond distances in the QM part
of IMOMM and the P-C(sp3) (1.843 Å) and C(Cp)-C(sp3) (1.499 Å)
distances in the MM part of IMOMM.
(25) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann,
R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,
R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,
J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-
Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian, Inc.: Pittsburgh, PA,
1998.
(26) (a) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and
Molecules; Oxford University Press: Oxford, United Kingdom; 1989. (b)
Ziegler, T. Chem. ReV. 1991, 91, 651.
(27) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785. (b) Becke,
A. D. J. Chem. Phys. 1993, 98, 5648. (c) Stephens, P. J.; Devlin, F. J.;
Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11 623.
(28) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
Acknowledgment. We wish to thank the Ministerio de
Ciencia y Tecnolog´ıa of Spain (DGI, Project BQU2001-4026
and BQU2002-04110-CO2-02) and Junta de Andaluc´ıa (PAI-
FQM 0188) for financial support. We also thank Johnson
Matthey plc for including us in their precious metal loan scheme.
Supporting Information Available: Tables of X-ray structural
data, including data collection parameters, positional and thermal
parameters, and bond distances and angles for complexes 1, 2,
3, and 10. Geometries of the calculated structures for the three
isomers in the A, B, C, and D systems (as Cartesian coordi-
nates). This material is available free of charge via the Internet
at http://pubs.acs.org.
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