Alternative mechanisms of the alkyne to vinylidene isomerization promoted by half-sandwich ruthenium complexes. X-ray crystal structure of [Cp*Ru = C = CHCOOMe(dippe)][BPh4] and [Cp*RuH(C ≡ CCOOMe(dippe)][BPh4] (dippe = 1,2-bis(diiso

Article abstract of DOI:10.1021/ja9701220

The complex [Cp*RuCl(dippe)] reacts with 1-alkynes in MeOH in the presence of NaBPh₄, yielding the metastable hydrido-alkynyl derivatives [Cp*Ru(H)(C ≡ CR)(dippe)][BPh₄] (R = COOMe, Ph or SiMe₃), intermediates in the forma

Full text of DOI:10.1021/ja9701220

J. Am. Chem. Soc. 1997, 119, 6529-6538
6529
Alternative Mechanisms of the Alkyne to Vinylidene
Isomerization Promoted by Half-Sandwich Ruthenium
Complexes. X-ray Crystal Structures of
[Cp*RudCdCHCOOMe(dippe)][BPh4] and
[Cp*RuH(CtCCOOMe)(dippe)][BPh4] (dippe )
1,2-bis(diisopropylphosphino)ethane; Cp* ) C5Me5)
Isaac de los R´ıos, Manuel Jime´nez Tenorio, M. Carmen Puerta,* and
Pedro Valerga
Contribution from the Departamento de Ciencia de Materiales e Ingenier´ıa Metalu´rgica y
Qu´ımica Inorga´nica, Facultad de Ciencias, UniVersidad de Ca´diz, Apartado 40,
11510 Puerto Real, Ca´diz, Spain
ReceiVed January 15, 1997X
Abstract: The complex [Cp*RuCl(dippe)] reacts with 1-alkynes in MeOH in the presence of NaBPh4, yielding the
metastable hydrido-alkynyl derivatives [Cp*Ru(H)(CtCR)(dippe)][BPh4] (R ) COOMe, Ph or SiMe3), intermediates
in the formation of the corresponding vinylidene complexes, to which these compounds rearrange both in solution
and in the solid state. The X-ray crystal structures of the isomers [Cp*RudCdCHCOOMe(dippe)][BPh4] and
[Cp*RuH(CtCCOOMe)(dippe)][BPh4] have been determined. Kinetic studies show that the mechanism for this
isomerization process seems to be dissociative and that it is inhibited in solution by strong acids. In contrast with
this, no hydrido-alkynyl complex has been observed in the course of the reaction of 1-alkynes with [CpRuCl-
(dippe)]. Instead, the alkyne adducts have been detected, and isolated in some cases. Such species have only been
observed in the Cp*Ru system for acetylene, and [Cp*Ru(η2-HCtCH)(dippe)]+ seems to be in equilibrium with the
corresponding hydrido-alkynyl complex [Cp*RuH(CtCH)(dippe)]+, which isomerizes to [Cp*RudCdCH2(dippe)]+
Via the formation of the π-alkyne complex. The effects on these tautomerization processes of the phosphine, Cp*,
and Cp ligands, as well as the R group of the alkyne, are discussed.
Introduction
plausible.3 A similar result was obtained from ab initio MO
calculations for the tautomerization of the ruthenium complex
[RuCl2(η2-HCtCH)(PH3)2] to [RudCdCH2(Cl)2(PH3)2], in
which the intermediate [RuCl2(H)(CtCH)(PH3)2] was shown
to be of very high energy and, therefore, highly unstable.5 It
appears that the mechanism involving oxidative addition is
difficult if the metal changes from d6 to d4, as in the case of
RuII to RuIV (or MnI to MnIII), but this process may take place
when the metal changes from d8 to d6, i.e. MI to MIII (M ) Co,
Rh, Ir).3 Thus, there are several examples in the chemistry of
these metals in which this sort of mechanism operates, i.e. in
the reaction of [RhCl(PiPr3)2] and [IrCl(PiPr3)2] with 1-alkynes.6
The π-adducts [MCl(HCtCR)(PiPr3)2] are formed first. Then,
these rearrange to the RhIII or IrIII hydrido-alkynyl intermediates
[M(H)(CtCR)Cl(PiPr3)2], and finally to the corresponding
vinylidene complexes [MdCdCHR(Cl)(PiPr3)2].6 In a similar
fashion, Bianchini and co-workers have shown7 that the 16-
electron fragment [Co(PP3)]+ (PP3 ) P(CH2CH2PPh2)3) reacts
with 1-alkynes, yielding π-alkyne adducts of the type [Co(η2-
HCtCR)(PP3)]+ which isomerize to the vinylidene complexes
[CodCdCHR(PP3)]+ passing through CoIII hydrido-alkynyl
intermediates [Co(H)(CtCR)(PP3)]+. At variance with this, the
The rearrangement of acetylene to its vinylidene isomer is a
thermodynamically disfavored process, given the fact that free
vinylidene :CdCH2 is ca. 44-47 kcal mol-1 less stable than
acetylene HCtCH.1 However, this process becomes thermo-
dynamically favorable on complexation to a metal center.2 Upon
coordination, the relative stability of acetylene and vinylidene
is reversed, the vinylidene complex being ca. 35 kcal mol-1
more stable than the corresponding acetylene adduct, as shown
by extended Hu¨ckel MO calculations.3 Several possible mech-
anisms have been proposed for this conversion. It was initially
suggested that oxidative addition of the alkyne to give an
hydrido-alkynyl metal complex could be a feasible pathway
for the formation of the corresponding vinylidene complex, Via
a concerted 1,3-hydrogen shift of the hydride from the metal to
the â-carbon atom of the alkynyl ligand.4 However, extended
Hu¨ckel calculations made on the d6 metal complex [CpMn(η2-
HCtCH)(CO)2] have shown that the concerted 1,3-hydrogen
shift in the intermediate hydrido-alkynyl complex [CpMn(H)-
(CtCH)(CO)2] would have a very high activation energy, and
a direct 1,2-hydrogen shift in the former complex seems more
X Abstract published in AdVance ACS Abstracts, June 15, 1997.
(1) (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. Jensen, J. H.; Morokuma, K.;
Gordon, M. S. J. Chem. Phys. 1994, 100, 1981.
(2) Bruce, M. I.; Swincer, A. G. AdV. Organomet. Chem. 1983, 22, 59
and references therein.
(3) Silvestre, J.; Hoffmann, R. HelV. Chim. Acta 1985, 68, 1461.
(4) Antonova, A. B.; Kolobova, N. E.; Petrovsky, P. V.; Lokshin, B.
V.; Obezyuk, N. S. J. Organomet. Chem. 1977, 137, 55.
(5) Wakatsuki, Y.; Koga, N.; Yamazaki, H.; Morokuma, K. J. Am. Chem.
Soc. 1994, 116, 8105.
(6) Wolf, J.; Werner, H.; Serhadli, O.; Ziegler, M. L. Angew. Chem.,
Int. Ed. Engl. 1983, 22, 414; Werner, H.; Ho¨hn, A. J. Organomet. Chem.
1984, 272, 105. Garc´ıa-Alonso, F. J.; Ho¨hn, A.; Wolf, J.; Otto, H.; Werner,
H. Angew. Chem., Int. Ed. Engl. 1985, 24, 406. Dziallas, M.; Werner, H.
J. Chem. Soc., Chem. Commun. 1987, 852.
(7) Bianchini, C.; Peruzzini, M.; Vacca, A.; Zanobini, F. Organometallics
1991, 10, 3697.
S0002-7863(97)00122-4 CCC: $14.00 © 1997 American Chemical Society

6530 J. Am. Chem. Soc., Vol. 119, No. 28, 1997
de los R´ıos et al.
related rhodium fragment [Rh(PP3)]+ reacts with 1-alkynes,
yielding RhIII hydrido-alkynyl derivatives, but these do not
rearrange to yield the corresponding vinylidenes.8 These
examples of hydrido-alkynyl to vinylidene rearrangements are
rather slow and presumably occur in a nonconcerted fashion.9
Very recently, an ab initio MO study on the transformation of
[RhCl(η2-HCtCH)(PH3)2] to [RhdCdCH2(Cl)(PH3)2] has shown
that this process may occur through either an intramolecular or
intermolecular proton transfer mechanism Via the RhIII oxidative
addition product [RhH(CtCH)(Cl)(PH3)2].10 In the case of
ruthenium, it has been possible to isolate the π-adducts such as
[CpRu(η2-HCtCR)(PR3)2]+ as intermediates in the formation
of the vinylidene complexes [CpRudCdCHR(PR3)2]+.11,12 The
isomerization in these species is expected to occur through a
direct 1,2-hydrogen shift, and no hydrido-alkynyl intermediates
have been detected, this being consistent with the affirmation
that such species are of very high energy in the case of d4 metal
complexes.3,5 In contrast with the cyclopentadienylruthenium
vinylidene complexes, the data on the related pentamethylcy-
clopentadienyl derivatives are much more scarce. In fact, the
first example of the activation of terminal alkynes with a Cp*Ru
complex, [Cp*RuCl(PMe2Ph)2], was reported only recently.13
On the other hand, the reports on the interaction of substituted
alkynes with transition metal complexes are relatively abundant,
but less so on similar processes involving acetylene, despite
the fact that most theoretical papers dealing with the problem
of alkyne-vinylidene tautomerization promoted by transition
metal complexes use unsubstituted acetylene for calcula-
tions.3,5,10 We now report that the hydrido-alkynyl RuIV
complexes [Cp*Ru(H)(CtCR)(dippe)][BPh4] (dippe ) 1,2-bis-
(diisopropylphosphino)ethane; R ) COOMe, Ph, SiMe3) are
formed upon reaction of [Cp*RuCl(dippe)]14 with Na[BPh4] and
HCtCR in MeOH. These compounds rearrange both in the
solid state and in solution to the vinylidene complexes
[Cp*RudCdCHR(dippe)][BPh4], being therefore feasible in-
termediates in the isomerization of 1-alkynes to vinylidene
complexes, as well as rare examples of an alkyne to vinylidene
rearrangement taking place at a d4 metal center.15 When the
reaction is carried out with acetylene HCtCH, both the η2-
alkyne and the hydrido-alkynyl isomers are formed, and these
rearrange to give finally the primary vinylidene complex. No
hydrido-alkynyl complexes have been isolated or detected in
the reaction of the cyclopentadienyl complex [CpRuCl(dippe)]
with 1-alkynes, suggesting that the role of the C5Me5 ligand in
these processes seems to be very important.13 In this work, we
compare the reactivity of the C5Me5 and C5H5 systems and also
describe the X-ray crystal structures of the two isomeric
compounds [Cp*RudCdCHCOOMe(dippe)][BPh4] and [Cp*Ru-
(H)(CtCCOOMe)(dippe)][BPh4]. A preliminary account of
this research has already been published.16
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. 1,2-
Bis(diisopropylphosphino)ethane,17 [CpRuCl(dippe)],14 [Cp*RuCl-
(dippe)],14 and [CpRu(Me2CO)(dippe)][BPh4]18 were prepared according
to reported procedures. IR spectra were recorded in Nujol mulls on
Perkin Elmer 881 or Perkin Elmer FTIR Spectrum 1000 spectropho-
tometers. NMR spectra were taken on 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}). The
phosphine protons for all the compounds appeared in the corresponding
1H NMR spectra as a series of overlapping multiplets in the range δ
0.5-3.0 ppm and were not assigned. Microanalysis were by Dr.
Manuel Arjonilla at the CSIC-Instituto de Ciencias Marinas de
Andaluc´ıa.
Preparation of Vinylidene Complexes [Cp*RudCdCHR(dippe)]-
[BPh4] (R ) COOMe, 1a; Ph, 1b; SiMe3, 1c; But, 1d). In a typical
preparation, a solution of [Cp*RuCl(dippe)] (0.25 g, ca. 0.5 mmol) in
MeOH (15 mL) was treated with an excess of the corresponding
1-alkyne. To this mixture was added an excess of solid NaBPh4 (0.3
g), and a microcrystalline precipitate was formed almost immediately.
The mixture was stirred for several minutes at room temperature. Then
the precipitate was filtered off, washed with EtOH and petroleum ether,
and dried in Vacuo. These compounds can be recrystallized from
acetone/EtOH. Yield: 75-80% in all cases.
1a: Anal. Calcd for C52H71BO2P2Ru: C, 69.3; H, 7.88. Found:
C, 69.9; H, 7.95. IR (Nujol): ν(CdC) 1588 cm-1, ν(CdO) 1689 cm-1
.
1H NMR (CDCl3): δ 1.82 (t, J(H,P), 1.2 Hz, C5(CH3)5), 3.64 (s,
COOCH3), 4.50 (t br, J(H,P) ∼ 8 Hz, RudCdCHCOOMe). 31P{1H}:
δ 75.3 s. 13C{1H}: 10.89 (s, C5(CH3)5), 18.33, 19.50, 19.90 (s, P(CH-
(CH3)2)2), 21.88 (t, J(C,P) ) 18.2 Hz, PCH2), 25.22 (q, J(C,P) ) 9.0
Hz, P(CH(CH3)2)2), 32.29 (m, P(CH(CH3)2)2), 51.52 (s, COOCH3),
104.40 (s, C5(CH3)5), 109.23 (s, RudCdCHCOOMe), 164.37 (s,
COOCH3), 338.10 (t, RudCdCHCOOMe, J(C,P) ) 14.2 Hz).
1b: Anal. Calcd for C56H73BP2Ru: C, 73.1; H, 7.95. Found: C,
72.7; H, 8.12. IR (Nujol): ν(CdC) 1595 cm-1 1H NMR (CDCl3):
.
δ 1.88 (s, C5(CH3)5), 4.86 (s br, RudCdCHPh), 7.12, 7.25 (m, C6H5).
31P{1H} δ 83.5 s. 13C{1H}: 11.19 (s, C5(CH3)5), 17.51, 18.31, 18.45,
18.74, 19.99 (s, P(CH(CH3)2)2), 21.39 (m, PCH2), 25.06 (m, P(CH-
(CH3)2)2), 32.51 (t, J(C,P) ) 16.4 Hz, P(CH(CH3)2)2), 103.33 (s, C5-
Me5), 115.97 (s, RudCdCHPh), 126.54, 128.70, 130.11 (s, C6H5),
345.30 (t, J(C,P) ) 13.7 Hz, RudCdCHPh).
1c: Anal. Calcd for C53H77BP2RuSi: C, 69.5; H, 8.42. Found: C,
69.8; H, 8.45. IR (Nujol): ν(CdC) 1604 cm-1 1H NMR (CDCl3):
.
δ 0.14 (s, Si(CH3)3), 1.81 (t, J(H,P) ) 2 Hz, C5(CH3)5), 3.16 (t, J(H,P)
) 12 Hz, RudCdCHSiMe3), 31P{1H}: δ 81.8 s. 13C{1H}: 4.091 (s,
RudCdCHSi(CH3)3), 13.36 (s, C5(CH3)5), 20.25, 20.94, 21.50, 21.81
(s, P(CH(CH3)2)2), 23.40 (t, J(C,P) ) 19 Hz, PCH2), 27.72 (t, J(C,P)
) 9.8 Hz, P(CH(CH3)2)2), 31.74 (m, P(CH(CH3)2)2), 95.30 (s,
RudCdCHSiMe3), 331.16 (t, J(C,P) ) 14 Hz, RudCdCHSiMe3)).
1d: Anal. Calcd for C54H77BP2Ru: C, 72.1; H, 8.57. Found: C,
72.4; H, 8.32. IR (Nujol): ν(CdC) 1634 cm-1 1H NMR (CDCl3):
.
δ 1.08 (s, C(CH3)3), 1.81 (s, C5(CH3)5), 3.28 (s br, RudCdCHCMe3).
31P{1H}: δ 83.4 s. 13C{1H}: 11.11 (s, C5(CH3)5), 18.61, 18.74, 19.73
20.18 (s, P(CH(CH3)2)2), 21.73 (t, J(C,P) ) 20 Hz, PCH2), 25.70 (t,
J(C,P) ) 9.2 Hz, P(CH(CH3)2)2), 32.72 (s, RudCdCHC(CH3)3), 32.93
(m, P(CH(CH3)2)2), 102.21 (s, C5Me5), 121.89 (s, RudCdCHCMe3),
330.6 (t, J(C,P) ) 13 Hz, RudCdCHCMe3).
Preparation of Hydrido-Alkynyl Derivatives [Cp*RuH(CtCR)-
(dippe)][BPh4] (R ) COOMe, 2a; Ph, 2b; SiMe3, 2c). These
compounds were obtained following a method analogous to that for
the corresponding vinylidene complexes, but reversing the order in
which the reagents are added: NaBPh4 is added first and then the
1-alkyne. The hydrido-alkynyl complexes precipitate from the reaction
mixture as white microcrystalline materials, in ca. 75-80% yield. All
these compounds rearrange to their vinylidene isomers both in solution
and in the solid state, except 2a, which only rearranges in solution.
For this reason, all compounds except 2a were not recrystallized or
Experimental Section
All synthetic operations were performed under a dry dinitrogen or
argon atmosphere by following conventional Schlenk or drybox
(8) Bianchini, C.; Masi, D.; Meli, A.; Peruzzini, M.; Ram´ırez, J. A.;
Vacca, A.; Zanobini, F. Organometallics 1989, 8, 2179.
(9) Bruce, M. I. Chem. ReV. 1991, 19, 197.
(10) Wakatsuki, Y.; Koga, N.; Werner, H.; Morokuma, K. J. Am. Chem.
Soc. 1997, 119, 360.
(11) Lomprey, J. R.; Selegue, J. P. J. Am. Chem. Soc. 1992, 114, 5518.
(12) Bullock, R. M. J. Chem. Soc., Chem. Commun. 1989, 165.
(13) Le Lagadec, R.; Roma´n, E.; Toupet, L.; Mu¨ller, U.; Dixneuf, P.
Organometallics 1994, 13, 5030.
(14) de los R´ıos, I.; Jime´nez-Tenorio, M.; Padilla, J.; Puerta, M. C.;
Valerga, P. J. Chem. Soc., Dalton Trans. 1996, 377.
(15) Nickias, P. N.; Selegue, J. P.; Young, B. A. Organometallics 1988,
7, 2248.
(16) de los R´ıos, I.; Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. J.
Chem. Soc., Chem. Commun. 1995, 1757.
(17) Fryzuk, M. D.; Jones, M. D.; Einstein, F. W. B. Organometallics
1984, 3, 185. Burt, T. A.; Chatt, J.; Hussain, W.; Leigh, G. J. J. Organomet.
Chem. 1979, 182, 203.
(18) de los R´ıos, I.; Jime´nez-Tenorio, M.; Padilla, J.; Puerta, M. C.;
Valerga, P. Organometallics 1996, 15, 4565.

Alkyne to Vinylidene Isomerization
J. Am. Chem. Soc., Vol. 119, No. 28, 1997 6531
analyzed. Crystals of 2a suitable for X-ray structure analysis were
obtained by layering with ethanol an acidic acetone solution of this
compound, made up using as solvent acetone containing a few drops
of HBF4.
g) in ethanol (15 mL). Concentration and cooling to -20 °C afforded
yellow-orange crystals. Yield: 0.27 g, 63%. Anal. Calcd for C49H63-
P2BO2Ru: C, 68.6, H 7.40. Found: C, 68.9; H, 7.28. IR (Nujol):
ν(CtC) 1857 cm-1, ν(CdO) 1705 cm-1 1H NMR (CDCl3): δ 3.85
.
(s, Ru(CH3OOCCtCCOOCH3), 5.22 (s, C5H5). 31P{1H}: δ 87.9 s.
13C{1H}: δ 18.66, 18.81, 18.95, 19.03 (s, P(CH(CH3)2)2), 22.28 (t,
J(C,P) ) 19.7 Hz, PCH2), 28.81 (t, J(C,P) ) 12.4 Hz, P(CH(CH3)2)2),
2a: IR (Nujol): ν(CtC) 2108 cm-1, ν(CdO) 1680 cm-1 1H NMR
.
(CD3COCD3, 223 K): 1H δ -8.55 (t, J(H,P) ) 27.6 Hz, RuH), 2.00
(s, C5(CH3)5), 3.60 (s, COOCH3), 31P{1H} (223 K): δ 75.5 s.
2b: IR (Nujol): ν(CtC) 2106 cm-1 1H NMR (CD3COCD3, 223
.
31.29 (t, J(C,P)
) 12 Hz, P(CH(CH3)2)2), 53.35 (s, Ru(H3-
COOCCtCCOOCH3)), 84.87 (s br, Ru(H3COOCCtCCOOCH3)),
87.66 (s, C5H5), 163.48 (s, Ru(H3COOCCtCCOOCH3)).
K): δ -8.79 (t, J(H,P) ) 29 Hz, RuH), 1.86 (s, C5(CH3)5), 7.11, 7.50
(m, C6H5), 31P{1H} (223 K) δ 73.5 s.
Preparation of [CpRu(η2-HCtCH)(dippe)][BPh4] (4e). To a
solution of [CpRuCl(dippe)] (0.23 g, 0.5 mmol) in MeOH (20 mL)
was added an excess of NaBPh4. Acetylene was bubbled through the
mixture. A yellow microcrystalline solid precipitates almost im-
mediately. It was filtered, washed with ethanol and petroleum ether,
and dried in Vacuo. Yield: 86%. This material appears always mixed
with small amounts of the primary vinylidene complex 3e, to which
4e isomerizes both in the solid state (slow) and in solution (faster).
For this reason, it was not analyzed, being characterized by IR and
2c: IR (Nujol): ν(CtC) 2030 cm-1 1H NMR (CD3COCD3, 223
.
K): δ -9.13 (t, J(H,P) ) 30.4 Hz, RuH), 0.06 (s, Si(CH3)3), 1.85 (s,
C5(CH3)5), 31P{1H} (223 K): δ 72.4 s.
Preparation of Vinylidene Complexes [CpRudCdCHR(dippe)]-
[BPh4] (R ) COOMe, 3a; Ph, 3b; But, 3d). These compounds were
obtained and recrystallized in a fashion analogous to that for the
pentamethylcyclopentadienyl derivatives 1a-d by starting from the
appropriate amounts of [CpRuCl(dippe)]. Yield: 75-80%.
3a: Anal. Calcd for C47H61BP2O2Ru: C, 67.9; H, 7.34. Found:
C, 67.6; H, 7.51. IR (Nujol): ν(CdC) 1641 cm-1, ν(CdO) 1701
NMR spectroscopy. IR (Nujol): ν(CtC) 1747 cm-1
.
1H NMR
cm-1
.
1H NMR (CD3COCD3): δ 3.62 (s, COOCH3), 4.91 (s,
(CDCl3, 243 K): δ 4.29 (t, J(H,P) ) 4.6 Hz, Ru(HCtCH), 4.80 (s,
C5H5). 31P{1H}: δ 88.0 s.
RudCdCHCOOCH3), 5.88 (s, C5H5). 31P{1H}: δ 97.18 s. 13C{1H}:
δ 18.66, 18.90, 19.06, 19.25 (s, P(CH(CH3)2)2), 22.85 (t, J(C,P) ) 19.9
Hz, PCH2), 30.08 (t, J(C,P) ) 17.3 Hz, P(CH(CH3)2)2), 30.48 (t, J(C,P)
) 12.0 Hz, P(CH(CH3)2)2), 51.17 (s, COOCH3), 90.53 (s, C5H5), 112.77
(s, RudCdCHCOOMe), 337.89 (t, J(C,P) ) 14.1 Hz, RudCd
CHCOOMe).
Reaction of [Cp*RuCl(dippe)] with HCtCH: [Cp*RuH(CtCH)-
(dippe)][BPh4] (2e), [Cp*Ru(η2-HCtCH)(dippe)][BPh4] (6e), and
[Cp*RudCdCH2(dippe)][BPh4] (1e). To a solution of [Cp*RuCl-
(dippe)] (0.25 g, ca. 0.5 mmol) in MeOH was added an excess of solid
NaBPh4. Acetylene was bubbled through the mixture, yielding an off-
white microcrystalline precipitate, which was filtered off, washed with
ethanol and petroleum ether, and dried in Vacuo. This material showed
to be a mixture of the hydrido-alkynyl complex 2e and the η2-alkyne
adduct 6e. Both compounds isomerize to the primary vinylidene 1e,
both in the solid state an in solution. Anal. Calcd for C50H69BP2Ru:
C, 71.2; H, 8.19. Found: C, 71.4; H, 8.08.
3b: Anal. Calcd for C51H63BP2Ru: C, 72.1; H, 7.42. Found: C,
72.2; H, 7.68. IR (Nujol): ν(CdC) 1624 cm-1 1H NMR (CDCl3):
.
δ 5.22 (s, RudCdCHPh), 5.44 (s, C5H5), 6.90 (t, J(H,H) ) 7.4 Hz,
C6H5), 7.14 (t, J(H,H) ) 7.4 Hz, C6H5), 7.27 (t, J(H,H) ) 7.4 Hz,
C6H5). 31P{1H}: δ 97.45 s. 13C{1H}: δ 18.74, 18.84, 19.01, 19.27
(s, P(CH(CH3)2)2), 22.72 (t, J(C,P) ) 19.7 Hz, PCH2), 30.22 (t, J(C,P)
) 4.3 Hz, P(CH(CH3)2)2), 30.85 (t, J(C,P) ) 4.9 Hz, P(CH(CH3)2)2),
89.60 (s, C5H5), 118.80 (s, RudCdCHPh), 126.57, 127.03, 128.88 (s,
RudCdCHC6H5), 345.51 (t, J(C,P) ) 15 Hz, RudCdCHPh).
3d: Anal. Calcd for C49H67BP2Ru: C, 71.0; H, 8.08. Found: C,
2e: IR (Nujol): ν(CtC) 1965 cm-1 1H NMR (CD3COCD3, 223
.
K): δ -8.83 (t, J(H,P) ) 30 Hz, RuH), 2.00 (s, C(CH3)5), 2.62 (t,
J(H,P) ) 2.9 Hz, RuCtCH), 31P{1H} (223 K): δ 73.2 s.
6e: IR (Nujol): ν(CtC) 1743 cm-1 1H NMR (CD3COCD3, 223
.
K): δ 1.70 (s, C(CH3)5), 4.83 (t, J(H,P) ) 5.2 Hz, Ru(HCtCH), 31P-
{1H} (223 K): δ 74.9 s.
70.8; H, 8.13. IR (Nujol): ν(CdC) 1648 cm-1 1H NMR (CDCl3):
.
1H δ 1.08 (s, RudCdCHC(CH3)), 3.84 (s br, RudCdCHCMe3), 5.32
(s, C5H5). 31P{1H}: δ 96.6 s. 13C{1H}: δ 19.03, 19.46, 19.61 (s, P(CH-
(CH3)2)2), 22.79 (m, PCH2), 30.72 (m, P(CH(CH3)2)2), 31.52 (m, P(CH-
(CH3)2)2), 32.46 (s, RudCdCHC(CH3)), 85.25 (s, RudCdCHCMe3),
89.01 (s, C5H5), 342.05 (t, J(C,P) ) 14 Hz, RudCdCHCMe3).
Preparation of [CpRudCdCH2(dippe)][BPh4] (3e). This com-
pound can be prepared by the same procedure described for the
vinylidene complexes 3a-3d, using HCtCSiMe3. Methanolysis of
the trimethylsilylvinylidene complex yields compound 3e. Yield: ca.
80%. Anal. Calcd for C45H59BP2Ru: C, 69.9; H, 7.63. Found: C,
1e: IR (Nujol): ν(CdC) 1619 cm-1 1H NMR (CDCl3): δ 1.83 (t,
.
J(H,P) ) 1.2 Hz, C(CH3)5), 3.49 (s br, RudCdCH2). 31P{1H}: δ 87.0
s. 13C{1H}: δ 10.92 (s, C(CH3)5), 18.07, 18.79, 19.38, 19.70 (s, P(CH-
(CH3)2)2), 21.35 (t, J(C,P) ) 20 Hz, PCH2), 25.84 (t, J(C,P) ) 10.2
Hz, P(CH(CH3)2)2), 30.00 (t, J(C,P) ) 16.2 Hz, P(CH(CH3)2)2), 95.99
(s, RudCdCH2), 102.42 (s, C5(CH3)5), 340.83 (t, J(C,P) ) 14.6 Hz,
RudCdCH2).
Neutral Alkynyl Complexes [Cp*Ru(CtCR)(dippe)] (R )
COOMe, 7a; Ph, 7b; SiMe3, 7c; But, 7d; H, 7e). A THF solution of
the corresponding vinylidene complex was treated with an excess of
solid KOBut. The mixture was stirred at room temperature for 1 h at
room temperature. Then, the solvent was removed in Vacuo. The
residue was extracted with toluene and the solution filtered through
Celite. Concentration, addition of petroleum ether, and cooling to -20
°C afforded crystals of these compounds.
69.6; H, 7.76. IR (Nujol): ν(CdC) 1628 cm-1 1H NMR (CDCl3):
.
δ 3.71 (s br, RudCdCH2), 5.37 (s, C5H5). 31P{1H}: δ 98.6 s. 13C-
{1H}: δ 18.80, 19.03, 19.43, 19.60 (s, P(CH(CH3)2)2), 23.12 (m, PCH2),
28.60 (m, P(CH(CH3)2)2), 30.21 (m, P(CH(CH3)2)2), 89.44 (s, C5H5),
99.34 (s, RudCdCH2), 337.29 (t, J(C,P) ) 15.1 Hz, RudCdCHCMe3).
Identification in Solution of η2-Alkyne Complexes [CpRu(η2-
HCtCR)(dippe)][BPh4] (R ) COOMe, 4a; Ph, 4b). Solutions of
the complex [CpRu(Me2CO)(dippe)][BPh4] in CD3COCD3, prepared
under inert atmosphere in NMR tubes, were frozen by inmersion into
liquid N2. One drop of the corresponding alkyne was added. The
solvent was allowed to melt. Then, the tubes were shaken, to mix the
reagents, and stored in an ethanol/liquid N2 bath. The samples prepared
in this way were studied by NMR at low temperatures, as indicated.
4a: 1H NMR (CD3COCD3) (193 K): 5.60 (s, C5H5), 4.47 (s br, Ru-
(HCtCCOOMe)). 31P{1H} (303 K): 90.1 s. 31P{1H} (193 K): 89.2,
93.5 (s br).
7a: Yield: 65%. Anal. Calcd for C28H50P2O2Ru: C, 57.8; H, 8.66.
Found: C, 57.5; H, 8.53. IR (Nujol): ν(CtC) 2031 cm-1, ν(CO) 1651
cm-1 1H NMR (C6D6): δ 1.81 (t, J(H,P) ) 1 Hz, C(CH3)5), 3.52 (s,
.
RuCtCCOOCH3). 31P{1H}: δ 88.4 s. 13C{1H}: δ 11.28 (s, C(CH3)5),
18.73, 19.30, 19.63, 20.90 (s, P(CH(CH3)2)2), 21.53 (t, J(C,P) ) 19.9
Hz, PCH2), 25.52 (t, J(C,P) ) 8.5 Hz, P(CH(CH3)2)2), 28.87 (m, P(CH-
(CH3)2)2), 50.54 (s, COOCH3), 93.08 (s, C5(CH3)5), 104.80 (s,
RuCtCCOOMe), 147.12 (t, J(C,P) ) 21.7 Hz, RuCtCCOOMe).
7b: Yield: 62%. Anal. Calcd for C32H52P2Ru: C, 64.1; H, 8.74.
Found: C, 64.4; H, 8.66. IR (Nujol): ν(CtC) 2063 cm-1 1H NMR
.
(CDCl3): δ 1.84 (s, C(CH3)5), 6.89, 7.06, 7.10 (m, RuCtCC6H5). 31P-
{1H}: δ 88.7 s. 13C{1H}: δ 11.19 (s, C(CH3)5), 18.89, 19.03, 19.51,
21.02 (s, P(CH(CH3)2)2), 21.31 (t, J(C,P) ) 19.5 Hz, PCH2), 25.46 (t,
J(C,P) ) 7.5 Hz, P(CH(CH3)2)2), 28.31 (t, J(C,P) ) 14.5 Hz, P(CH-
(CH3)2)2), 91.91 (s, C5(CH3)5), 121.85 (s, RuCtCPh), 125.04, 127.65,
129.95 (s, RuCtCC6H5), RuCtCC6H5 not observed.
4b: 1H NMR (CD3COCD3) (183 K): 5.56 (s, C5H5), 4.49 (s br, Ru-
(HCtCPh)). 31P{1H} (243 K): 88.7 s. 31P{1H} (183 K): 84.6, 93.5
(d, J(P,P) ) 21.5 Hz).
Preparation of [CpRu(η2-MeOOCCtCCOOMe)(dippe)][BPh4]
(5). To a solution of [CpRuCl(dippe)] (0.23 g, ca. 0.5 mmol) in THF
were added MeOOCCtCCOOMe (0.2 g, ca. 0.5 mmol) and AgBF4
(0.1 g). A precipitate of AgCl was formed. The mixture was stirred
at room temperature for 15 min. Then, it was centrifuged, to remove
AgCl. To the resulting solution was added an excess of NaBPh4 (0.3
7c: Yield: 60%. Anal. Calcd for C29H56P2RuSi: C, 58.5; H, 9.47.
Found: C, 58.7; H, 9.43. IR (Nujol): ν(CtC) 1925 cm-1 1H NMR
.
(C6D6): δ 0.35 (s, RuCtCSi(CH3)3), 1.84 (t, J(H,P) ) 1.2 Hz,

6532 J. Am. Chem. Soc., Vol. 119, No. 28, 1997
de los R´ıos et al.
C(CH3)5). 31P{1H}: δ 88.8 s. 13C{1H}: δ 2.44 (s, RuCtCSi(CH3)3),
11.32 (s, C(CH3)5), 18.97, 19.45, 19.73 (s, P(CH(CH3)2)2), 21.42 (m,
PCH2), 25.42 (m, P(CH(CH3)2)2), 28.27 (m, P(CH(CH3)2)2), 92.01 (s,
C5(CH3)5), 110.94 (s, RuCtCSiMe3), 158.23 (t, J(C,P) ) 21.3 Hz,
RuCtCSiMe3).
Table 1. Summary of Data for the Crystal Structure Analysis of
1a and 2a
1a
2a
formula
fw
C52H71BO2P2Ru
901.96
C52H71BO2P2Ru
901.96
7d: Yield: 61%. Anal. Calcd for C30H56P2Ru C, 62.2; H, 9.74.
crystal size (mm)
crystal system
space group
cell parameters
0.28 × 0.10 × 0.17 0.20 × 0.08 × 0.45
Found: C, 62.3; H, 9.71. IR (Nujol): ν(CtC) 2077 cm-1 1H NMR
.
triclinic
orthorhombic
(C6D6): δ 1.39 (s, RuCtCC(CH3)3), 1.87 (t, J(H,P) ) 1.2 Hz, C(CH3)5).
31P{1H}: δ 89.2 s. 13C{1H}: δ 11.48 (s, C(CH3)5), 19.16, 19.34, 19.83
(s, P(CH(CH3)2)2), 21.37 (t, J(C,P) ) 19.5 Hz, PCH2), 25.44 (t, J(C,P)
) 7.6 Hz, P(CH(CH3)2)2), 28.00 (t, J(C,P) ) 14.5 Hz, P(CH(CH3)2)2),
33.73 (s, RuCtCC(CH3)3), 65.84 (s, RuCtCC(CH3)3), 91.08 (s, C5-
(CH3)5), 104.86 (t, J(C,P) ) 22 Hz, RuCtCCMe3), 113.73 (s,
RuCtCCMe3).
P1h (no. 2)
a ) 13.275(2) Å
b ) 14.672(3) Å
c ) 12.172(2) Å
R ) 96.81(2)°
â ) 91.09(1)°
γ ) 94.36(1)°
2350.9(7)
2
P212121 (no. 19)
a ) 16.167(6) Å
b ) 28.707(4) Å
c ) 10.257(6) Å
volume (Å3)
4760(5)
4
1.258
7e: Yield: 67%. Anal. Calcd for C26H48P2Ru: C, 59.6; H, 9.24.
Z
F
Found: C, 59.4; H, 9.18. IR (Nujol): ν(CH) in the alkynyl, 3240 cm-1
,
calcd (g cm-3
)
1.274
ν(CtC) 1925 cm-1 1H NMR (C6D6): δ 1.85 (s, C(CH3)5), 1.98 (t,
.
λ(Mo KR) (Å)
µ(Mo KR) (cm-1
F(000)
0.71069
4.30
0.71069
4.25
J(H,P) ) 2 Hz, Ru(CtCH)). 31P{1H}: δ 88.5 s. 13C{1H}: δ 11.45
(s, C(CH3)5), 19.08, 19.47, 19.83 (s, P(CH(CH3)2)2), 21.31 (m, PCH2),
25.49 (m, P(CH(CH3)2)2), 28.26 (m, P(CH(CH3)2)2), 91.55 (s, RuCtCH),
92.23 (s, C5(CH3)5; RuCtCH not observed.
)
956
1912
transmision factors
scan speed (ω) (deg min-1
2θ interval
0.86-1.00
0.92-1.00
)
8
8
Neutral Alkynyl Complexes [CpRu(CtCR)(dippe)] (R ) COOMe,
8a; Ph, 8b; But, 8d; H, 8e). These compounds were obtained following
an experimental procedure identical to that for 7a-7e, starting from
the corresponding cyclopentadienyl vinylidene complex 3a-3e.
8a: Yield: 68%. Anal. Calcd for C23H40P2O2Ru: C, 54.0; H, 7.88.
Found: C, 54.1; H, 7.82. IR (Nujol): ν(CtC) 2028 cm-1, ν(CdO)
5° < 2θ < 50°
5° < 2θ < 50°
3880
no. of measured reflections 7516
no. of unique reflections
7201 (Rint ) 0.052) 3733 (Rint ) 0.150)
no. of obsd reflns (I > 3σI) 4322
2821
383
7.37
0.064
0.073
0.02
no. of parameters
refln/parameter ratio
Ra
495
8.73
0.058
0.069
5.70
1650 cm-1 1H NMR (CDCl3): δ 3.55 (s, RuCtCCOOCH3), 4.96 (s,
.
-2
b
Rw (w ) σF
)
RuC5H5). 31P{1H}: δ 100.8 s. 13C{1H}: δ 18.93, 19.64, 19.75, 20.46
(s, P(CH(CH3)2)2), 23.66 (t, J(C,P) ) 19.8 Hz, PCH2), 27.33 (t, J(C,P)
) 14.5 Hz, P(CH(CH3)2)2), 29.36 (t, J(C,P) ) 10.7 Hz, P(CH(CH3)2)2),
51.19 (s, COOCH3), 80.79 (s, C5H5), 104.07 (s, RuCtCCOOMe),
126.74 (m, RuCtCCOOMe).
maximum ∆/σ
in final cycle
GOF
1.69
1.53
2
a R ) Σ||Fo| - |Fc||/Σ|Fo|. b Rw ) (Σw(|Fo| - |Fc|)2/Σw|Fo| )1/2
.
8b: Yield: 69%. Anal. Calcd for C27H42P2Ru: C, 61.2; H, 7.99.
Found: C, 61.1; H, 7.91. IR (Nujol): ν(CtC) 2069 cm-1 1H NMR
.
were calculated from the uncertainties in the slope and intercept of the
best-fit lines of the Eyring plots.
(CDCl3): δ 4.94 (s, RuC5H5), 6.89-7.10 (m, RuCtCC6H5). 31P-
{1H}: δ 102.1 s. 13C{1H}: δ 18.85, 19.82, 19.89, 20.65 (s, P(CH-
(CH3)2)2), 23.90 (t, J(C,P) ) 19.7 Hz, PCH2), 27.27 (m, P(CH(CH3)2)2),
29.36 (m, P(CH(CH3)2)2), 79.74 (s, C5H5), 109.53 (s, RuCtCPh),
118.42 (t, J(C,P) ) 23.3 Hz, RuCtCPh), 122.48, 127.62, 130.33,-
151.00 (s, RuCtCC6H5).
Experimental Data for the X-ray Crystal Structure Determina-
tions. A summary of crystallographic data for compounds 1a and 2a
is given in Table 1. X-ray measurements were made on crystals of
the appropriate size, which were mounted onto a glass fiber and
transferred to an AFC6S-Rigaku automatic diffractometer, using Mo
KR graphite-monochromated radiation. Cell parameters were deter-
mined from the settings of 25 high-angle reflections. Data were
collected by the ω-2θ scan method for compound 1a and the ω scan
method for 2a. Lorentz, polarization, and absorption (ψ-scan method)
corrections were applied. A small decay correction was also applied
for each of the compounds. Reflections having I > 3σ(I) were used
for structure refinement. All calculations for data reduction, structure
solution, and refinement were carried out on a VAX 3520 computer at
the Servicio Central de Ciencia y Tecnolog´ıa de la Universidad de
Ca´diz, using the TEXSAN19 software system and ORTEP20 for plotting.
All the structures were solved by the Patterson method and anisotro-
pically refined by full-matrix least-squares methods for all non-hydrogen
atoms. The hydride atom in compound 2a was located on a regular
difference Fourier map, and it was not refined. Most of the other
hydrogen atoms were included at idealized positions and not refined.
Maximum and minimum peaks in the final difference Fourier maps
were +0.95 and -0.80 e Å-3 for 1a and +0.60 and -0.94 e Å-3 for
2a. Selected bond lengths and angles for each compound are listed in
Tables 2 and 3.
8d: Yield: 57%. Anal. Calcd for C25H46P2Ru: C, 58.9; H, 9.10.
Found: C, 58.7; H, 9.06. IR (Nujol): ν(CtC) 2089 cm-1 1H NMR-
.
(C6D6): δ 1.34 (s, RuCtCC(CH3)3), 4.87 (s, RuC5H5). 31P{1H}: δ
103.6 s. 13C{1H}: δ 18.26, 19.45, 19.62, 20.86 (s, P(CH(CH3)2)2),
23.97 (m, PCH2), 27.15 (m, P(CH(CH3)2)2), 28.93 (m, P(CH(CH3)2)2),
33.02 (s, RuCtCC(CH3)3), 79.33 (s, C5H5), 114.28 (s, RuCtCCMe3),
125.21 (m, RuCtCCMe3).
8e: Yield: 70%. Anal. Calcd for C21H38P2Ru: C, 55.6; H, 8.44.
Found: C, 55.5; H, 8.52. IR (Nujol): ν(CtC) 1930 cm-1; ν(CsH)
in the alkynyl, 3285 cm-1 1H NMR (C6D6): δ 1.79 (t, J(H,P) ) 1.96
.
Hz, RuCtCH), 4.92 (s, RuC5H5). 31P{1H} 101.0 s. 13C{1H} 18.93,
19.87, 19.99, 21.18 (s, P(CH(CH3)2)2), 23.95 (t, J(C,P) ) 19.7 Hz,
PCH2), 27.38 (t, J(C,P) ) 14.6 Hz, P(CH(CH3)2)2), 29.44 (t, J(C,P) )
10.2 Hz, P(CH(CH3)2)2), 80.05 (s, C5H5), 94.22 (s, RuCtCH), 128.30
(m, RuCtCH).
Kinetics Studies of the Hydrido-Alkynyl or η2-Alkyne to Vi-
nylidene Isomerization. Samples of the corresponding hydrido-
alkynyl or η2-alkyne complex, prepared as described above, were
immersed into a liquid N2/ethanol bath, to “freeze” the isomerization
process during transport and handling. The sample was removed from
the bath and inserted into the precooled probe of the Varian UNITY-
400 spectrometer at 203 K. Once shims were adjusted, the probe was
warmed to the desired temperature. The NMR temperature controller
was previously calibrated against a methanol sample, the reproducibility
being (0.5 °C. 31P{1H} NMR spectra were recorded for at least 3
half-lives at regular intervals using the spectrometer software for
accurate time control. Peak intensities were analyzed from stacked
plots of the 31P{1H} NMR spectra. First-order rate constants were
derived from the least-squares best-fit lines of the ln(intensity) Versus
time plots. The uncertainty in the isomerization rate constants
represents one standard deviation ((σ) derived from the slope of the
best fit line. Uncertainties in the activation enthalpies and entropies
Results
The complex [Cp*RuCl(dippe)] reacts readily with 1-alkynes
in MeOH at room temperature yielding the corresponding
vinylidene complexes [Cp*RudCdCHR(dippe)]+ (R ) COOMe,
1a; Ph, 1b; SiMe3, 1c; But, 1d), isolable as tetraphenylborate
salts. These are crystalline solids, soluble in polar organic
solvents except alcohols, which display one strong ν(CdC) band
(19) TEXSAN, Single-Crystal Structure Analysis Software, version 5.0,
Molecular Structure Corp., Texas, 1989.
(20) Johnson, C. K. ORTEP, A Thermal Ellipsoid Plotting Program; Oak
Ridge National Laboratory; Oak Ridge, TN, 1965.

Alkyne to Vinylidene Isomerization
J. Am. Chem. Soc., Vol. 119, No. 28, 1997 6533
Table 2. Selected Bond Distances (Å) and Angles (deg) for
[Cp*RudCdCHCOOMe(dippe)][BPh4]
Intramolecular Distancesa
atom
atom
distance
atom
atom
distance
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
P(1)
P(2)
2.348(2)
2.380(2)
2.26(2)
2.26(2)
2.30(2)
2.23(2)
2.31(2)
2.24(2)
2.44(2)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
O(1)
O(2)
O(2)
C(4B)
C(5A)
C(5B)
C(11)
C(13)
C(13)
C(14)
C(12)
C(13)
2.32(2)
2.42(2)
2.36(2)
1.807(9)
1.19(1)
1.34(1)
1.46(1)
1.32(1)
1.46(1)
C(1A)
C(1B)
C(2A)
C(2B)
C(3A)
C(3B)
C(4A)
C(11)
C(12)
Intramolecular Bond Anglesb
atom
atom
atom
angle
P(1)
P(1)
P(2)
C(13)
Ru(1)
C(11)
O(1)
O(1)
O(2)
Ru(1)
Ru(1)
Ru(1)
O(2)
C(11)
C(12)
C(13)
C(13)
C(13)
P(2)
82.50(8)
90.1(3)
93.7(3)
115.1(8)
170.5(8)
129(1)
124(1)
125(1)
111.7(8)
C(11)
C(11)
C(14)
C(12)
C(13)
O(2)
C(12)
C(12)
Figure 1. ORTEP drawing of the cation [Cp*RudCdCHCOOMe-
(dippe)]+ with 50% probability thermal ellipsoids.
a Distances are in angstroms. Estimated standard deviations in the
least significant figure are given in parentheses. b Angles are in degrees.
Estimated standard deviations in the least significant figure are given
in parentheses.
ruthenium (CR) appears as a very low resonance, near 350 ppm,
in the 13C{1H} NMR spectra. This strongly deshielded reso-
nance for CR is a characteristic feature of vinylidene complexes,
being due to the sign and magnitude of the paramagnetic
contributions to nuclear shielding.23 One singlet is observed
in the 31P{1H} NMR spectra of these compounds, suggesting
the equivalence of the phosphorus atoms. These spectral data
are consistent with a three-legged piano-stool structure for these
complexes, as has been observed for other related derivatives.
The X-ray crystal structure of compound 1a has been deter-
mined. An ORTEP view of the cation [Cp*RudCdCHCOOMe-
(dippe)]+ is shown in Figure 1. Selected bond lengths and
angles are listed in Table 2. The ruthenium atom appears in a
formally octahedral coordination, in which the Cp* ligand fills
three coordination positions, the other three being occupied by
the two phosphorus atoms of the chelating dippe, and by the
CR atom of the (methoxycarbonyl)vinylidene group. The Ru-
C(11) bond distance of 1.807(9) Å corresponds to a double bond,
and it is shorter than the reported Ru-C separations for
cyclopentadienylruthenium vinylidene complexes, i.e. 1.845-
(7) Å in [CpRudCdCHMe(PMe3)2][PF6]22 or 1.843(1) Å in
[CpRudCdCH2(PMe2Ph)2][BF4],11 being slightly longer than
that in one of the few structurally characterized Cp*Ru
vinylidene complexes, 1.76(1) Å in [Cp*RudCdCH2(PMe2-
Ph)2][PF6].13 These parameters are indicative of an increased
electron-releasing capability of Cp*RuP2 moieties compared to
that for their Cp counterparts. The C(11)-C(12) bond distance,
1.32(1) Å, corresponds to a double bond and compares well
with previously reported data. The vinylidene group assembles
almost linearly with the Ru atom, having a Ru-C(11)-C(12)
angle of 170.5(8)°.
Table 3. Selected Bond Distances (Å) and Angles (deg) for
[Cp*RuH(CtCCOOMe)(dippe)][BPh4]
Intramolecular Distances
atom
atom
distance
atom
atom
distance
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
P(1)
P(2)
C(1)
C(2)
C(3)
C(4)
2.340(4)
2.342(5)
2.30(2)
2.26(2)
2.24(2)
2.25(2)
Ru(1)
Ru(1)
Ru(1)
C(11)
C(12)
C(5)
C(11)
H(1)
C(12)
C(13)
2.25(2)
2.04(2)
1.35
1.18(2)
1.43(3)
Intramolecular bond angles
atom
atom
atom
angle
P(1)
P(1)
P(1)
P(1)
P(1)
P(1)
P(1)
P(1)
P(2)
P(2)
P(2)
P(2)
P(2)
P(2)
P(2)
C(11)
Ru(1)
C(11)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
Ru(1)
C(11)
C(12)
P(2)
87.5(2)
161.6(5)
142.2(5)
108.6(5)
102.0(5)
126.8(5)
80.9(5)
52.48
106.6(5)
124.2(5)
160.7(5)
151.9(5)
117.1(6)
82.3(5)
67.78
C(1)
C(2)
C(3)
C(4)
C(5)
C(11)
H(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(11)
H(1)
H(1)
C(12)
C(13)
123.75
175(2)
173(2)
a Distances are in angstroms. Estimated standard deviations in the
least significant figure are given in parentheses. b Angles are in degrees.
Estimated standard deviations in the least significant figure are given
in parentheses.
Whereas vinylidene complexes 1a-d are obtained by reaction
of [Cp*RuCl(dippe)] with the corresponding 1-alkyne in MeOH,
followed by NaBPh4, if the order in which the reagents are added
is reversed, different products are isolated. Thus, if NaBPh4 is
added first, and then the 1-alkyne, a white microcrystalline
precipitate is formed almost immediately. These materials
near 1600 cm-1 in their IR spectra. The 1H NMR spectra show
the signal corresponding to the proton on the â-carbon of the
vinylidene ligands as one triplet or broad singlet in the range
3-5 ppm, a pattern which has also been observed for other
half-sandwich ruthenium phosphine vinylidene complexes of
the type [CpRudCdCHR(P)2]+ (Cp ) C5H5 or C5Me5; P2 )
one bidentate or two monodentate phosphine ligands).11-13,21,22
The carbon atom of the vinylidene ligand directly attached to
(21) Consiglio, G.; Morandini, F. Inorg. Chim. Acta 1987, 127, 79.
Consiglio, G.; Morandini, F.; Ciani, G. F.; Sironi, A. Organometallics 1986,
5, 1976.
(22) Bruce, M. I.; Wong, F. S.; Skelton, B. W.; White, A. H. J. Chem.
Soc., Dalton Trans. 1982, 2203.
(23) Czech, P. T.; Xe, X.-Q.; Fenske, R. F. Organometallics 1990, 9,
2016.

6534 J. Am. Chem. Soc., Vol. 119, No. 28, 1997
de los R´ıos et al.
Scheme 1. Suggested Reaction Sequence for the Alkyne to
Vinylidene Isomerization through Hydrido-Alkynyl
Complexes [Cp*RuH(CtCR)(dippe)]+
display one strong band near 2100 cm-1 in their IR spectra
attributable to ν(CtC) and consistent with the formation of the
hydrido-alkynyl complexes [Cp*RuH(CtCR)(dippe)][BPh4]
(R ) COOMe, 2a; Ph, 2b; SiMe3, 2c) (Scheme 1). In the case
Figure 2. ORTEP drawing of the cation [Cp*RuH(CtCCOOMe)-
(dippe)]+ with 50% probability thermal ellipsoids. Hydrogen atoms,
except hydride, are omitted.
t
of R ) Bu, the only product isolated is always the vinylidene
complex 1d, irrespective of the order in which the reagents are
added. The hydrido-alkynyl complexes 2a-c are formally
derived from the insertion of the metal atom into the C-H bond
of the 1-alkyne and, therefore, must be considered RuIV (d4)
species. These compounds rearrange to their respective vi-
nylidene isomers 1a-c when they are dissolved in acetone,
dichloromethane, or tetrahydrofuran at room temperature.
Furthermore, this isomerization takes place also in the solid state
for compounds 2b,c at room temperature, but not for 2a, which
seems to be stable as a solid at this temperature. A solid state
hydrido-alkynyl to vinylidene rearrangement has been recently
observed for cobalt and rhodium complexes, i.e. the transforma-
tion of [CoH(CtCR)(pp3)][BPh4] to [CodCdCHR(pp3][BPh4]7
or [RhCl(H)(CtCSiMe3)(PiPr3)2] to [RhdCdCHSiMe3(Cl)(P-
iPr3)2],24 but this is the first report of such process involving
ruthenium. The isomerization is stopped at low temperatures,
both in the solid state and in solution. Therefore, it is possible
to obtain the NMR of 2a-c by dissolving the complexes in
acetone-d6 at -50 °C. The hydride resonance appear as one
interactions with the substituents of the alkynyl group. This
ligand appears linearly assembled to ruthenium, with a Ru(1)-
C(11)-C(12) angle of 175(2)°. The bond lengths Ru(1)-C(11),
2.04(2) Å and C(11)-C(12), 1.18(2) Å, compare well with those
found in the only structurally characterized ruthenium hydrido-
alkynyl complex, cis-[RuH(CtCPh)(pp3)]‚C6H6, 2.078 and
1.16(1) Å, respectively.26 These parameters also match those
found in the alkynyl-dihydrogen complex [Ru(H2)(CtCPh)-
(dippe)2][BPh4], 2.01(1) and 1.19(2) Å.27 The hydride atom
was localized in a Fourier difference map, and it was not refined.
The Ru(1)-H(1) separation was found to be 1.35 Å, rather short
compared to 1.57(8) Å in cis-[RuH(CtCPh)(pp3)]‚C6H6,26 but
similar to the values reported for other ruthenium hydride
complexes, such as [CpRuH(PMe3)2] (1.36(8) Å)25 or [RuH-
(C6H6)(dippe)][BPh4] (1.32 Å).28 All other bond lengths and
angles are in the expected range and are unexceptional. The
kinetics of the hydrido-alkynyl to vinylidene isomerization have
been studied by NMR spectroscopy, following an experimental
procedure analogous to that used by Chinn and Heinekey for
the study of the dihydrogen to dihydride tautomerization in half-
sandwich ruthenium complexes.29 Samples of complexes 2a-c
were prepared in acetone-d6 at -80 °C, and then inserted into
the spinner and lowered into the NMR precooled probe. At
temperatures below -50 °C, the main product observed by 1H
and 31P{1H} NMR spectroscopy was almost exclusively the
hydrido-alkynyl tautomer, being also present very minor
amounts of the corresponding vinylidene complex. As the
temperature rises, the signals corresponding to the hydrido-
alkynyl species decrease and the signals attributable to the
vinylidene tautomer increase their intensities with time. Kinetic
data acquired following the rate of disappearance of the
phosphorus resonance of the hydrido-alkynyl complex in the
31P{1H} NMR spectra were consistent with a first-order process.
Data were collected over 3 half-lives or more at different
temperatures, and rate constants were obtained from the slope
of the least-squares best-fit lines of the ln(intensity) Vs time
1
high-field triplet in the H NMR spectra, whereas the 31P{1H}
consists of one sharp singlet. The spectral data are consistent
with a transoid “four-legged” piano-stool structure for these
compounds. The isomerization to vinylidene in solution
prevented initially to grow crystals of these materials, until we
discovered that the rearrangement process is inhibited in solution
by small amounts of a strong acid, such as HBF4‚OEt2. In this
fashion, careful recrystallization of 2a from THF/ethanol in the
presence of one drop of HBF4‚OEt2 afforded colorless crystals,
which were subjected to X-ray structure analysis, taking
advantage of the stability as solid of this compound, which does
not isomerize at room temperature. An ORTEP view of the
cation [Cp*RuH(CtCCOOMe)(dippe)]+ is shown in Figure 2.
Selected bond lengths and angles are listed in Table 3. The
complex cation has a transoid “four-legged” piano-stool struc-
ture, consistent with spectral data. The P(1)-Ru(1)-P(2) plane
forms an angle of 101.21° with the plane defined by the C5
ring of the Cp* group. This arrangement is very similar to that
adopted by ruthenium dihydrides such as [Cp*RuH2(dippe)]-
[BPh4]18 and [CpRuH2(PMe3)2][BF4],25 but in our case, the angle
deviates from the ideal value of 90°, possibly to minimize steric
(26) Bianchini, C.; Frediani, P.; Masi, D.; Peruzzini, M.; Zanobini, F.
Organometallics 1994, 13, 4616.
(27) Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. J. Chem. Soc.,
Chem. Commun. 1993, 1750.
(24) Werner, H.; Baum, M.; Schneider, D.; Windmu¨ller, B. Organome-
tallics 1994, 13, 1089.
(25) Lemke, F. R.; Brammer, L. Organometallics 1995, 14, 3980.
(28) de los R´ıos, I.; Jime´nez-Tenorio, M.; Jime´nez-Tenorio, M. A.; Puerta,
M.C.; Valerga, P. J. Organomet. Chem. 1996, 525, 57.
(29) Chinn, M. S.; Heinekey, D. M. J. Am. Chem. Soc. 1990, 113, 5166.

Alkyne to Vinylidene Isomerization
J. Am. Chem. Soc., Vol. 119, No. 28, 1997 6535
vinylidene complex [CpRudCdCH2(dippe)][BPh4] (3e) as the
final product of this reaction. This behavior has precedents in
the literature, i.e. the formation of [CpFedCdCH2(dppm)][BF4]
from [CpFeCtCSiMe3(dppm)],30 but this process does not occur
for the related Cp* complex 1c, which is stable. None of the
vinylidene complexes prepared in this work react with alcohols
to yield alkoxy-carbene species, as it commonly occurs in other
cases.31 The fact that no Cp hydride-alkynyl derivatives were
isolated indicates that, if these are intermediates in the formation
of the corresponding vinylidene complexes, they should be short-
lived species that rearrange at room temperature before pre-
cipitation as tetraphenylborate salts takes place. In an attempt
to detect possible intermediates, the reaction of 1-alkynes with
the labile acetone adduct [CpRu(Me2CO)(dippe)][BPh4]18 at low
temperature was monitored by NMR spectroscopy. This
compound was chosen because it has shown to be an excellent
precursor for the preparation of complexes [CpRu(L)(dippe)]+
(L ) neutral donor molecule), being readily converted to the
dinitrogen complex [CpRu(N2)(dippe)]+ in dichloromethane
solution under N2.18 Thus, upon addition of HCtCR (R )
COOMe, Ph) and examination of the CD2Cl2 solution by 31P-
{1H} NMR spectroscopy at -50 °C, the resonances due to the
dinitrogen adduct dissappear, being replaced by a new, broad
signal which does not correspond to the vinylidene complex.
This signal splits into two separate broad resonances when the
temperature is lowered. For phenylacetylene, these resonances
resolve into doublets at 183 K, having a J(P,P) coupling constant
of 21.5 Hz (Figure 4). No signals attributable to hydridic
Figure 3. Plot of ln(k/T) vs 1/T (K-1) for the irreversible isomerization
of [Cp*RuH(CtCR)(dippe)]+ to [Cp*RudCdCHR(dippe)]+ (R )
COOMe (b); SiMe3 (2); Ph (0)).
Table 4. Activation Parameters for the Hydrido-Alkynyl to
Vinylidene and η2-Alkyne to Vinylidene Rearrangements Studied in
this Work
∆Hq
∆Sq
∆G298
process
(kcal mol-1
)
(kcal mol-1
)
(kcal mol-1
)
2a f 1a
2b f 1b
2c f 1c
4a f 3a
4e f 3e
2e f 1e
6e f 1e
17 ( 1
24 ( 1
21 ( 2
26.6 ( 0.5
29 ( 2
25 ( 2
26 ( 2
-9 ( 1
17 ( 1
4 ( 1
21 ( 1
26 ( 1
10 ( 1
12 ( 1
20 ( 1
19 ( 1
20 ( 2
1
protons were observed in the relevant region of the H NMR
20.3 ( 0.5
21 ( 2
spectrum. These spectral data are consistent with the formation
in solution of the π-alkyne adducts [CpRu(η2-HCtCR)(dippe)]+
(R ) COOMe, 4a; Ph, 4b).
22 ( 2
22 ( 2
plots. These constants are invariant with the starting concentra-
tion of the complex. The rate constants at 273 K are (2.5 (
0.3) × 10-3 s-1 for the isomerization of 2a, (1.01 ( 0.02) ×
10-3 s-1 for 2b, and (1.0 ( 0.3) × 10-3 s-1 for 2c. Thus, the
rearrangement is faster for 2a, which bears on the alkynyl ligand
the R group having the most electron-attracting effect. Activa-
tion parameters for these systems were derived from an Eyring
plot for each of the series of rate constants determined at
different temperatures (Figure 3), yielding values which are
listed in Table 4. It has been previously noted for the
isomerization of hydrido-alkynyl complexes of cobalt that the
activation energy of the rate-determining step seems to be
influenced by the 1-alkyne substituent.7 This fact, together with
the lack of data in the literature apart from those on the cobalt
system, makes difficult the comparison of the thermodynamic
functions. However, the values obtained for 2b are similar in
magnitude to those for the rearrangement of [CoH(CtCPh)-
(pp3)][BPh4] to [CodCdCHPh(pp3)][BPh4] (∆Hq ) 31 ( 1 kcal
mol-1, ∆Sq ) 28 ( 1 cal K-1 mol-1, ∆G298 ) 22 ( 2 kcal
mol-1).7 No hydrido-alkynyl complexes have been isolated
or detected in the reaction of the cyclopentadienyl derivative
[CpRuCl(dippe)] with 1-alkynes, and only vinylidene species
[CpRudCdCHR(dippe)][BPh4] (R ) COOMe, 3a; Ph, 3b; But,
3d) have been obtained. These vinylidene complexes have
spectral properties which match those of their Cp* homologues,
including the presence of one ν(CdC) band in the IR spectra
and of one low-field signal in the 13C{1H} NMR spectra due to
the CR of the vinylidene group. The structure for these
compounds is hence assumed to be similar to that found by
X-ray diffraction for 1a, but having Cp instead of Cp*. It is
interesting to note that, in the course of the reaction of [CpRuCl-
(dippe)] with HCtCSiMe3, the C-Si bond is cleaved, presum-
ably by the alcohol used as the solvent, yielding the primary
The fluxional behavior arises from the rotation of the 1-alkyne
ligand around the metal-carbon bond. When the temperature
decreases, this movement is “frozen”, causing the nonequiva-
lence of the phosphorus atoms. The rotation barrier around the
Ru-alkyne bond has been estimated from the variable-temper-
ature 31P{1H} NMR data,32 being 8 kcal mol-1 for 4a and 11
kcal mol-1 for 4b. All attempts to isolate these π-alkyne
complexes as solids were unsuccessful, due to the fact that they
rearrange irreversibly to their vinylidene isomers 3a,3b as
temperature is raised. At variance with the hydrido-alkynyl
complexes, addition of a strong acid does not inhibit these
rearrangement processes in solution. The kinetics of the
isomerization 4a f 3a was studied by NMR spectroscopy. The
process is first order, with rate constants varying from (6.1 (
0.1) × 10-4 s-1 at 283 K to (1.4 ( 0.1) × 10-2 s-1 at 303 K.
From the studies at different temperatures activation parameters
were obtained (Figure 5): ∆Hq ) 26.6 ( 0.5 kcal mol-1, ∆Sq
) 21 ( 1 cal K-1 mol-1, and ∆G298 ) 20.3 ( 0.5 kcal mol-1
.
These values, which appear also in Table 4, resemble those
(30) Gamasa, M. P.; Gimeno, J.; Lastra, E.; Blanca, M. M. Organome-
tallics 1992, 11, 1373.
(31) Bruce. M. I.; Duffy, D. N.; Humphrey, M. G.; Swincer, A. G. J.
Organomet. Chem 1985, 282, 383. Bruce, M. I.; Swincer, A. G. Aust. J.
Chem. 1980, 33, 1471. Bruce, M. I.; Swincer, A. G.; Thomson, B. J.; Wallis
R. C. Aust. J. Chem. 1980, 33, 2605. Pilette, D.; Ouzzine, K.; Le Bozec,
H.; Dixneuf, P. H.; Rickard, C. E. F.; Roper, W. R. Organometallics 1992,
11, 809.
(32) Gu¨nther, H. NMR Spectroscopy, 2nd ed.; John Wiley & Sons:
Chichester, U.K., 1995.

6536 J. Am. Chem. Soc., Vol. 119, No. 28, 1997
de los R´ıos et al.
Figure 6. Plot of ln(k/T) vs 1/T (K-1) for the irreversible isomerization
of (A) [Cp*RuH(CtCH)(dippe)]+ to [Cp*RudCdCH2(dippe)]+ (O);
(B) [Cp*Ru(η2-HCtCH)(dippe)]+ to [Cp*RudCdCH2(dippe)]+ (b);
[CpRu(η2-HCtCH)(dippe)]+ to [CpRudCdCH2(dippe)]+ (0).
NMR spectrum consists of one singlet at 87.9 ppm, whereas
the carbon atoms of the MeOOCCtCCOOMe group directly
attached to Ru appear as one broad signal at 84.87 ppm in the
13C{1H} NMR spectrum. No analogous compound has been
obtained having Cp* as coligand. Furthermore, no π-alkyne
complexes were detected in the course of the reaction of
[Cp*Ru(η2-C2H4)(dippe)][BPh4],18 which dissociates ethylene
very easily, with 1-alkynes at low temperature. The only
product observed was the corresponding hydrido-alkynyl
derivative, which rearranges to its vinylidene isomer at higher
temperatures. These data suggest that the formation of meta-
stable hydrido-alkynyl intermediates is only feasible in the case
of Cp* complexes and that for Cp compounds a more standard
direct isomerization occurs from the π-alkyne adduct to the
corresponding vinylidene complex, consistent with data reported
in the literature for other ruthenium complexes.
Figure 4. Variable-temperature 31P{1H} NMR spectrum of [CpRu-
(η2-HCtCPh)(dippe)][BPh4] (4b) in CD2Cl2.
The reaction of both [CpRuCl(dippe)] and [Cp*RuCl(dippe)]
with acetylene, HCtCH, deserves a separate, detailed comment.
When acetylene is bubbled through a solution of [CpRuCl-
(dippe)] in MeOH containing NaBPh4, a precipitate of [CpRu-
(η2-HCtCH)(dippe)][BPh4] (4e) is immediately obtained. This
compound displays one medium IR band at 1747 cm-1
corresponding to ν(CtC) in the η2-alkyne ligand. The
acetylene protons appear in the 1H NMR spectrum as one triplet
at 4.29 ppm, J(H,P) ) 4.6 Hz, whereas one singlet is observed
in the 31P{1H} NMR spectrum. 4e rearranges to the primary
vinylidene complex 3e both in the solid state and in solution.
The rate of rearrangement was measured in solution by 31P-
{1H} NMR spectroscopy, the half-life being 7.9 min at 30 °C,
with the activation parameters (Figure 6) shown in Table 4.
This process is slower than the isomerization of the π-alkyne
adduct 4a to 3a, but much faster than similar rearrangements
reported in the literature, i.e. [CpRu(η2-HCtCH)(PMe2Ph)2]+
to [CpRudCdCH2(PMe2Ph)2]+ (t1/2 ) 18 min at 65 °C)11 or
[CpRu(η2-HCtCH)(PMe3)2]+ to [CpRudCdCH2(PMe3)2]+ (t1/2
) 5 h at 60 °C).12
Figure 5. Plot of ln(k/T) vs 1/T (K-1) for the irreversible isomerization
of [CpRu(η2-HCtCCOOMe)(dippe)]+ to [CpRudCdCHCOOMe-
(dippe)]+.
found for the isomerization of [CpRu(HCtCMe)(PMe3)2]+ to
[CpRudCdCHMe(PMe3)2]+ in MeCN (∆Hq ) 23.4 ( 0.9 kcal
mol-1, ∆Sq ) 3.9 ( 0.9 cal K-1 mol-1, and ∆G298 ) 22 ( 1
kcal mol-1). For comparison purposes, the stable π-alkyne
complex [CpRu(η2-MeOOCCtCCOOMe)(dippe)][BPh4] (5)
been prepared and characterized in full as a model for the
spectral properties of this sort of compounds. 5 was obtained
by reaction of [CpRuCl(dippe)] with MeOOCCtCCOOMe in
the presence of AgBF4 acting as chloride scavenger. This
compound displays one medium IR band at 1857 cm-1 due to
ν(CtC) of the η2-alkyne ligand, together with another at 1705
cm-1 attributable to ν(CdO) in the ester group. The 31P{1H}
The product of the reaction of [Cp*RuCl(dippe)] with
acetylene in MeOH containing NaBPh4 is a white microcrys-
talline material which showed to be a mixture of two isomers,

Alkyne to Vinylidene Isomerization
J. Am. Chem. Soc., Vol. 119, No. 28, 1997 6537
Scheme 2. Interaction of [Cp*RuCl(dippe)] with HCtCH
for most reported cationic vinylidene complexes.12,13,33 The IR
spectra ot these compounds are dominated by the strong ν(CtC)
absorption band near 2000 cm-1, having unexceptional NMR
spectral properties that do not require further comment. All
these compunds are protonated by HBF4‚OEt2, yielding back
the corresponding vinylidene complex in all cases, irrespective
of the solvent and the temperature. In no case has the formation
of a hydrido-alkynyl derivative as the product of the protona-
tion of neutral alkynyl complexes been detected by NMR
spectroscopy.
Discussion
The isomerization of 1-alkynes to vinylidene complexes at
the moieties {[Cp*Ru(dippe)]+} and {[CpRu(dippe)]+} has been
shown to occur by two alternative pathways, either Via RuIV
hydrido-alkynyl complexes or through the formation of π-alkyne
adducts as intermediates. These two pathways of isomerization
have been previously observed for other transition metal
complexes,6,7,11,13 but this is the first report in which metastable
RuIV hydrido-alkynyl complexes have been detected and
characterized as intermediates in the rearrangement of 1-alkyne
to vinylidene complexes. The tautomerization Via the π-alkyne
adducts is thought to occur by a slippage of the η2-alkyne ligand
leading to σ-η1 coordination, followed by a subsequent 1,2-
hydrogen migration to yield the vinylidene complex (mechanism
A):2-5,9
namely the hydrido-alkynyl derivative [Cp*RuH(CtCH)-
(dippe)][BPh4] (2e), and the π-alkyne complex [Cp*Ru(η2-
HCtCH)(dippe)][BPh4] (6e), as inferred from IR and NMR
spectral data. Thus, the IR spectrum of this mixture displays
bands at 1965 and 1743 cm-1 attributable to ν(CtC) in the
hydrido-alkynyl 2e and π-alkyne 6e, respectively. The hydride
proton of 2e appears as one triplet at -8.83 ppm in the 1H NMR
spectrum (223 K, acetone-d6), a pattern similar to that observed
for the related hydrido-alkynyl derivatives 2a-c, whereas
another triplet at 4.83 ppm, with a smaller coupling constant
J(H,P) ) 5.2 Hz, corresponds to the protons of the η2-alkyne
ligand. The 31P{1H} NMR spectrum displays one singlet for
each of the isomers, as expected. Both 2e and 6e rearrange to
the primary vinylidene [Cp*RudCdCH2(dippe)][BPh4] (1e) in
the solid state and in solution. The rearrangement in the solid
state is faster for 6e than for 2e, and this allows us to obtain
solid samples containing only 2e and 1e, by just leaving the
mixture standing at room temperature for some time. The 31P-
{1H} NMR spectrum of these samples at -50 °C showed
initially signals due to the hydrido-alkynyl and vinylidene
complexes, but at higher temperatures, the π-alkyne complex
6e is formed at the expense of 2e. This observation is supported
also by spin saturation transfer experiments. The rearrangement
of 2e and 6e to 1e occurs at essentially the same rate, the half-
life being 26 min at 303 K. The activation parameters, listed
in Table 4, have identical values within the experimental error
(Figure 6). At difference with the other hydrido-alkynyl to
vinylidene isomerizations presented in this work, the rearrange-
ment 2e f 1e does not seem to be inhibited by strong acids.
All of these observations suggest that there is possibly an
equilibrium between the hydrido-alkynyl and π-alkyne isomers,
which is however difficult to study due to the irreversible
isomerization to vinylidene. The equilibrium is shifted to the
hydrido-alkynyl tautomer, since this is the most abundant
species in the mixture in all cases. However, the observed rate
of isomerization corresponds probably to that of the π-alkyne
adduct. If we assume that this process occurs faster than the
direct isomerization of 2e to vinylidene, this compound would
convert to 6e to maintain the equilibrium and, hence, its rate of
disappearance would be the same as that for 6e. In this fashion,
the rearrangement of 2e to 1e will occur Via the formation of
6e (Scheme 2), and the isomerization of the latter is not inhibited
by strong acids, as it has been already observed for 4a,4b.
In our case, kinetic data for the rearrangement of η2-alkyne
complexes to vinylidene are similar to those reported in the
literature for the isomerization of related compounds,11,12 and
hence, it is likely that these processes take place according to
the concerted mechanism shown above. However, a different
mechanism operates when the tautomerization occurs Via
hydrido-alkynyl complexes and a concerted 1,3-hydrogen shift
has been proposed (mechanism B):2,3,9
However, this mechanism was found to be energetically too
costly for RuII (d6) complexes.3,5 This affirmation has been
supported by the fact that all hydrido-alkynyl complexes of
ruthenium reported until now were stable species which do not
rearrange to their vinylidene isomers.7,27 For the hydrido-
alkynyl complexes 2a-c, a number of experimental facts
suggest that the isomerization proceeds in a nonconcerted
fashion, so the mechanism B proposed above is not strictly
applicable. As shown in Scheme 1, once the hydrido-alkynyl
complex is formed, the hydride ligand dissociates as a proton,
yielding the corresponding neutral alkynyl complex. Protonation
of this compound at the â-carbon yields the vinylidene complex.
Addition of a strong acid inhibits the dissociation of the hydride
as proton and, therefore, the isomerization, as a consequence
of the common ion effect. This is a thermodynamic (not kinetic)
effect, since it only depends on the relative strength as acid of
the hydrido-alkynyl complex and that of the added acid. The
isomerization by a concerted mechanism would not be affected
by the addition of acid. On the other hand, the isomerization
of a 1:1 mixture of 2a or 2c with the labeled derivative [Cp*Ru-
All vinylidene complexes prepared in this work react with a
strong base such as KOBut, yielding the corresponding neutral
alkynyl complexes [Cp*RuCtCR(dippe)] (R ) COOMe, 7a;
Ph, 7b; SiMe3, 7c; But, 7d; H, 7e) or [CpRuCtCR(dippe)] (R
) COOMe, 8a; Ph, 8b; But, 8d; H, 8e), as has been observed
(33) Haquette, P.; Pirio, N.; Touchard, D.; Toupet, L.; Dixneuf, P. H. J.
Chem. Soc., Chem. Commun. 1993, 163.

6538 J. Am. Chem. Soc., Vol. 119, No. 28, 1997
de los R´ıos et al.
(D)(CtCPh)(dippe)][BPh4] occurs with scrambling of deute-
rium, and mixtures of [Cp*RudCdCHR(dippe)]+/[Cp*Rud
CdCDR(dippe)]+ (R ) COOMe or SiMe3) and [Cp*Rud
CdCHPh(dippe)]+/[Cp*RudCdCDPh(dippe)]+ are observed
by NMR spectroscopy, indicative of the dissociative nature of
the process. Consistent with this, the activation entropy is
positive in all cases except for the isomerization of 2a, which
is negative. This negative value could be a consequence of the
errors affecting the determination of the thermodynamic func-
tions, particularly the activation entropy, and may have no
mechanistic significance, but it could also result from the fact
that the isomerization takes place in two steps, the first one
being dissociative and the second one associative. This seems
to be consistent with the absence of isotopic effect observed
for the isomerization of [Cp*Ru(D)(CtCPh)(dippe)]+ to
[Cp*RudCdCDPh(dippe)]+. Thus, the overall rearrangement
process occurs according to a dissociative 1,3-hydrogen shift,
which appears to be the same as that proposed for the
isomerization of [Co(H)(CtCR)(PP3)]+ to [CodCdCHR-
(PP3)]+.7
possibly due to the fact that no equilibrium exists between the
hydrido-alkynyl and the η2-alkyne tautomers, the former being
much more stable than the latter given the strong tendency of
CoI complexes to undergo oxidative addition leading to CoIII
(d6) complexes, but this does not seems to be the case for RuII/
RuIV systems. The competition between oxidative addition and
side-on coordination of the alkyne is affected not only by
electronic factors but also by steric ones. The Cp* ligand is
bulkier than Cp, and hence, the steric interactions are more
important in its complexes. Thus, the η2-coordination of an
alkyne, specially for those bearing bulky R groups is sterically
more demanding than the η1-bonding mode found in hydrido-
alkynyl complexes. Only small alkyne substituents would make
possible the isolation of η2-alkyne complexes with the Cp*
ligand, i.e. in case of C2H2, leading to [Cp*Ru(η2- C2H2)(dippe)]-
[BPh4]. This is also consistent with the observations made on
the literature regarding the effect of steric interactions in the
stabilization of half-sandwich η2-alkyne complexes, such as
[CpRu(η2-C2H2)(PMe2Ph)2][BF4]11 or [CpRu(η2-alkyne)(iPr-
DAB)][CF3SO3] (iPr-DAB ) 1,4-diisopropyl-1,4-diaza-1,3 -b-
i
We can consider now the factors that determine which of
the isomerization mechanisms is going to operate for half-
sandwich ruthenium complexes. The mechanism involving the
formation of a hydrido-alkynyl intermediate requires C-H
activation in the 1-alkyne and oxidative addition, this being
unnecessary if the isomerization occurs via slippage in the
π-alkyne adduct. This may explain why the latter mechanism
seems to be more common than the former. For complexes of
the type [CpRuXP2] (Cp ) C5H5 or C5Me5; X ) halide; P2 )
one bidentate or two monodentate phosphine ligands), dissocia-
tion of halide leads to 16-electron species of the type
[CpRuP2]+,14,34 which have been isolated in some instances,35
these being reactive toward 1-alkynes. For these species, there
is a competition between oxidative addition and direct side-on
coordination of the alkyne to achieve the 18-electron configu-
ration. For the series of compounds prepared in this work, only
those having the stronger electron releasing Cp* ligand undergo
oxidative addition. If the R group on the alkyne has a strong
electron-attracting effect, i.e. COOMe or Ph, the C-H is more
activated toward cleavage and therefore the oxidative addition
is expected to occur more easily. The SiMe3 may have a similar
effect, due to the presence of empty d-orbitals at the silicon
atom, although at this stage it is not possible to establish the
extent to which these orbitals are involved. Interestingly, in
the case of R ) But, which has the inverse effect, no hydrido-
alkynyl or η2-alkyne complexes have been detected, and
therefore, little can be said about its possible mechanism of
isomerization. For acetylene, a mixture of both the hydrido-
alkynyl and η2-alkyne complexes is observed. These two
species seem to be in equilibrium, suggesting that their stability
is comparable. However, the isomerization possibly occurs
through a concerted 1,2-hydrogen shift in the η2-acetylene
adduct (Scheme 2), which should be the minimum energy
reaction pathway to the vinylidene complex. Bianchini et al.
have observed for the isomerization of [Co(η2-HCtCR)(PP3)]+
to [CodCdCHR(PP3)]+ that the π-alkyne adduct rearranges
first to [CoH(CtCR)(PP3)]+ and then to vinylidene.7 This is
utadiene, PrNdCH-CHdNiPr).36 The bulkiness of the sub-
stituents of the phosphine ligand is also important. No Cp*Ru
hydrido-alkynyl complexes have been detected with phosphines
such as 1,2-bis(diphenylphosphino)ethane (dppe) or 1,2-bis-
(dimethylphosphino)ethane (dmpe). Dppe has steric require-
ments similar to those of dippe, but it is a poorer donor, whereas
dmpe has electron releasing capabilities similar to dippe, but it
is sterically much less demanding. However, it has been
possible to isolate hydrido-alkynyl complexes of the type
[Cp*RuH(CtCR)(PR3)2][BPh4], containing large, strong electron-
releasing monodentate phosphines, which will be reported
elsewhere.37 It appears clear that bulky ligands, good donors
of electron density, favor the mechanism of isomerization to
vinylidene involving oxidative addition, specially in case of
alkynes bearing electron-attracting groups, whereas for com-
plexes with poorer donor and less bulky ligands, the rearrange-
ment will occur through a concerted 1,2-hydrogen shift in the
π-alkyne adduct.
The mechanisms of isomerization to vinylidene of either
π-alkyne and hydrido-alkynyl derivatives in the solid state
might be related to the processes observed in solution but are
more complex and difficult to study due to the larger number
of factors affecting the structural changes in the solid state
associated with the isomerization. We are currently studying
these rearrangement processes by a number of spectral tech-
niques, and the results will be reported in due course.
Acknowledgment. The authors thank Mr. Juan Miguel
Duarte Santos (Servicio Central de Ciencia y Tecnolog´ıa,
Universidad de Ca´diz) for efficient NMR service and the
Ministerio de Educacio´n y Ciencia of Spain (DGICYT, Project
PB94-1306) and Junta de Andaluc´ıa (Grupo 1103) for financial
support.
Supporting Information Available: CIF file deposited
electronically. See any current masthead page for Internet
access instructions.
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(37) de los R´ıos, I.; Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P.
Manuscript in preparation.