Ruthenium arene derivatives with PN hemilabile ligands. P-C cleavage and phosphine to phosphinite transformation

Article abstract of DOI:10.1021/om049438o

The synthesis of ruthenium arene derivatives with hemilabile ligands was investigated. An unexpected reactivity of the ligand was observed during the course of the synthesis which was transformed by the reaction with methanol into diarylphosphinite. The transformation of [RuCl₂(arene)(κ] ¹-PN)] type neutral derivatives in to the cationic species [RuCl(arene)κ²-PN)]X was achieved. The protonation of the neutral derivatives with HBF₄ resulted in the formation of [RuCl ²(arene)(κ¹-PNH)]BF₄ which exhibited a hydrogen bond.

Full text of DOI:10.1021/om049438o

5694
Organometallics 2004, 23, 5694-5706
Ruthenium Arene Derivatives with PN Hemilabile
Ligands. P-C Cleavage and Phosphine to Phosphinite
Transformation
Agust´ın Caballero,† Fe´lix A. Jalo´n,*,† Blanca R. Manzano,† Gustavo Espino,‡
Mercedes Pe´rez-Manrique,‡ Antonio Mucientes,§ Francisco J. Poblete,§ and
Miguel Maestro
Departamento de Quı´mica Inorga´nica, Orga´nica y Bioquı´mica, Facultad de Quı´micas,
Universidad de Castilla-La Mancha, Avenida Camilo J. Cela 10, 13071 Ciudad Real, Spain,
Departamento de Quı´mica, Facultad de Ciencias, Universidad de Burgos,
Plaza Misael Ban˜uelos s/n, 09001 Burgos, Spain, Departamento de Qu´ımica Fı´sica,
Facultad de Quı´micas, Universidad de Castilla-La Mancha, Avenida Camilo J. Cela 10,
13071 Ciudad Real, Spain, and Departamento de Qu´ımica Fundamental,
Facultade de Ciencias, Universidade da Corun˜a, Campus da Zapateira,
15071 A Corun˜a, Spain
Received July 23, 2004
Complexes of formula [RuCl2(arene)(κ1-dpim)] (dpim ) 2-(diphenylphosphino)-1-meth-
ylimidazole) (arene ) p-cymene, 1a; C6H6, 1b) were prepared by the reaction of [RuCl2(p-
cymene)]2 or [RuCl2(C6H6)(CH3CN)] with dpim. Complexes 1a and 1b were structurally
characterized by NMR spectroscopy and X-ray diffraction. The reaction of these precursors
-
with BF4 salts led, in dichloromethane, to cationic complexes of formula [RuCl(arene)(κ2-
dpim)]BF4 (arene ) p-cymene, 2a; C6H6, 2b). However, in methanol the products were
unexpected phosphinite derivatives of the type [RuCl(arene)(HImMe){κ1-PPh2(OMe)}]A (A
) BF4, arene ) p-cymene, 3a; C6H6, 3b; A ) BPh4, arene ) p-cymene, 3d) (ImMe )
methylimidazole). This transformation implies the existence of an easy P-C bond cleavage
and phosphine functionalization with methanol at room temperature. The precursors 1a,b
or the analogous derivative with 2-(diphenylphosphino)pyridine (PPh2py), [RuCl2(p-cymene)-
(κ1-PPh2py)], 1c, reacted with HBF4 to give cationic derivatives by protonation of the imidazole
or the pyridine fragment, [RuCl2(arene)(κ1-PNH)]BF4 (PNH ) dpimH, arene ) p-cymene,
4a; C6H6, 4b; PNH ) PPh2pyH, arene ) p-cymene, 4c). In these compounds the existence
of an asymmetric and bifurcated hydrogen bond NH‚‚‚Cl2 has been structurally determined
(even by X-ray studies for 4a,b). Complexes 2a and 4a also yield the corresponding and
analogous phosphinite derivatives in the presence of methanol-d4 but at a markedly slower
rate. NMR and spectrophotometric studies provided information concerning the formation
of the phosphinite derivatives. It was concluded that the phosphine is not functionalized if
it is not coordinated and that, very probably, a methanol solvatesintermediate between 1a
and 2asparticipates in the P-C bond cleavage and allows the aforementioned transforma-
tion. Some preliminary catalytic tests involving the transfer hydrogenation of cyclohexanone
and the hydrogenation of phenylacetylene have also been carried out.
Introduction
unique examples of reactivity.3 In recent years special
attention has been paid to the preparation and coordi-
nation of hemilabile P,O-donor ligands and, in particu-
lar, to phosphinoether compounds.4 Potential P,N-donor
molecules, although less frequently used, have received
increased attention in the past few years as hemilabile
ligands.2,5 An important application of complexes with
hemilabile ligands is in catalysis, and several different
processes have been analyzed.5a,6 Theoretical studies
concerned with this application have been performed.7
Arene complexes of ruthenium have been extensively
studied as catalyst precursors.5a,8 On the other hand,
the potentially hemilabile P,N ligand 2-(diphenylphos-
The concept of hemilability was first introduced by
Rauchfuss1 referring to the labile coordination of several
ligands bearing soft and hard donor atoms. These
ligands and their coordination chemistry2 have received
increased interest in recent years. In general, the hard
donor center is weakly coordinated and allowssby
decoordinationsthe binding of substrates that induce
† Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica,
Universidad de Castilla-La Mancha.
‡ Universidad de Burgos.
§ Departamento de Qu´ımica F´ısica, Universidad de Castilla-La
Mancha.
Universidade da Corun˜a.
(3) Davies, J. A.; Hartley, F. R. Chem. Rev. 1979, 81, 2658.
(4) (a) Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27. (b)
Slone, C. S.; Weinggerger, D. A.; Mirkin, C. A. Prog. Inorg. Chem. 1999,
48, 233.
(1) Jeffrey, J. C.; Rauchfuss, T. B Inorg. Chem. 1979, 18, 2658.
(2) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680-
699.
10.1021/om049438o CCC: $27.50 © 2004 American Chemical Society
Publication on Web 10/28/2004

Ruthenium Arene Derivatives
Chart 1
Organometallics, Vol. 23, No. 24, 2004 5695
to ascertain whether the presence of the free nitrogen
atom in the case of the monocoordinated ligand could
play a role similar to that of the added base in the case
of transfer hydrogenation.
Interestingly, during the course of the synthesis of
the new ruthenium derivatives we found an unexpected
reactivity of the ligand, which was transformed, by
reaction with methanol, into a diarylphosphinite. These
ligands are important in the field of asymmetric cataly-
sis,13 and their preparation usually requires multistep
and complicated procedures. A discussion concerning the
role played by phosphine coordination on the Ru center
and the possible mechanism of this transformation is
also included. We also investigated whether this behav-
ior was also exhibited by the similar complex containing
the more frequently used ligand 2-(diphenylphosphino)-
pyridine5a,b,14 (PPh2py) (see Chart 1).
phino)-1-methylimidazole, dpim (see Chart 1), has been
studied very little. This compound was first reported
in 1993,9 although a more convenient synthetic route
was subsequently published in 2001.10 Some complexes
of late transition metals with the dpim ligand have been
described,10,11 and we have reported new ruthenium
derivatives containing this ligand in the three possible
coordination modes: monodentate, bidentate chelate,
and bridge.12 When coordinated as a bidentate system,
the relative 1,3-positions of the donor atoms in the dpim
ligand are associated with a strained angle in the
metallacycle after κ2-coordination, a situation that could
favor partial decoordination of this ligand. When mono-
coordinated by the phosphorus atom, the ligand offers
a free nitrogen that, as a basic center, could help in the
activation of the substrates. With these ideas in mind,
we decided to synthesize and characterize new arene
ruthenium derivatives containing the dpim ligand and
to undertake an initial assessment of their catalytic
behavior in hydrogenation processes. It was of interest
Results and Discussion
Preparation of the New Complexes. The phos-
phine dpim (PN) was prepared in two steps basically
in accordance with the method reported by Nishikawa,10
i.e., the reaction of N-methylimidazole with n-BuLi and
reaction of the resulting salt with PClPh2. The ligand
dpim reacts with the dimeric compounds [RuCl2(arene)]2
(arene ) p-cymene, C6H6) to give complexes of formula
[RuCl2(arene)(κ1-PN)] (arene ) p-cymene, 1a; C6H6, 1b).
The poor solubility of the starting benzene derivative
lowers the yield of complex 1b, which is more con-
veniently prepared by the reaction of the phosphine with
the monomeric adduct [RuCl2(C6H6)(NCCH3)].15 Com-
plexes 1a and 1b were used as starting materials for
the preparation of other new complexes according to
Scheme 1.
The reactions of 1a,b with TlBF4 in dichloromethane
gave the cationic complexes [RuCl(arene)(κ2-dpim)]BF4
(arene ) p-cymene, 2a; C6H6, 2b) by elimination of the
chloride group and subsequent chelation of the phos-
phine. In marked contrast, a similar reaction with the
addition of a solution of NaBF4 or NaBPh4 in methanol
yielded the cationic phosphinito complexes [RuCl(are-
ne)(MeImH)(κ1-PPh2OMe)]A (A ) BF4, arene ) p-
cymene, 3a; C6H6, 3b; A ) BPh4, arene ) p-cymene,
3d) (MeIm ) methylimidazole). These complexes can
be considered the final products of a P-C(imidazolyl)
bond activation and transfer of the MeIm fragment as
the result of a nucleophilic attack of MeOH at the
phosphorus group. Mechanistic considerations will be
discussed below. The P-C bond activation by incoming
nucleophiles in metal complexes has very few literature
precedents,16 and it is noteworthy that, in the cases of
complexes 3a, 3b, and 3d, the reaction is carried out
under very mild conditions. As stated above, the prepa-
ration of this type of ligand is usually a complicated
process. Illustrative examples are (S)-BINAPO,17 glu-
(5) (a) Moldes, I.; de la Encarnacio´n, E.; Ros, J.; Alvarez-Larena,
A.; Piniella, J. F. J. Organomet. Chem. 1998, 566, 165. (b) Espinet, P.;
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J.; van Leeuwen, P. W. N. M.; Vrieze, K.; Fraanje, J.; Goubitz, K.; Spek,
A. L. J. Chem. Soc., Dalton Trans. 1996, 3163. (e) Crociani, L.; Bandoli,
G.; Dolmella, A.; Basato, M.; Corain, B. Eur. J. Inorg. Chem. 1998,
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Thornton-Pett, M.; Jutand, A.; Tooze, R. P. Organometallics 1999, 18,
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62. (j) Braunstein, P.; Naud, F.; Dedieu, A.; Rohmer, M. M.; DeCian,
A.; Rettig, S. J. Organometallics 2001, 20, 2966. (k) Romeo, R.; Scolaro,
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M.; Nagai, K.; Yamada, K.; Miwa, Y.; Taga, T.; Tomioka, K. J. Am.
Chem. Soc. 2002, 124, 8932. (f) Roch-Neirey, C.; Le Bris, N.; Laurent,
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T.; Zabel, M. Organometallics 2003, 22, 1741. (e) Nagashima, H.;
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Miyazaki, K.; Matsubara, K.; Kirchner, K. Coord. Chem. Rev. 2003,
245, 177. (f) Ozdemir, I.; Cetinkaya, E.; Cetinkaya, B.; Cicek, M.;
Semeril, D.; Bruneau, C.; Dixneuf, P. H. Eur. J. Inorg. Chem. 2004,
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Edwards, P. G.; Newman, P. D.; Tooze, R. P.; Coles, S. J.; Hursthouse,
M. B. J. Chem. Soc., Dalton Trans. 1998, 3771. (c) Dervisi, A.; Edwards,
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777.

5696 Organometallics, Vol. 23, No. 24, 2004
Caballero et al.
Scheme 1
cophinite,18 ProNOP,19 valNOP,20 and alaNOP,21 or
ProNOP22 derivatives. In the synthesis of these ligands
the last step, where the phosphinite functional group
is generated, involves the reaction of an alcohol with a
phosphorus derivative under very harsh conditions.
The complex analogous to 1a bearing p-cymene as the
arene and PPh2Py as the phosphine, [RuCl2(p-cymene)-
(κ1-PPh2py)] (1c), which has been reported previously,5a
was synthesized in order to analyze the possible forma-
tion of the corresponding phosphinito derivative analo-
gous to 3a with PPh2py as the phosphine. However, all
attempts to prepare this derivative failed and the
cationic complex [RuCl(p-cymene)(κ2-PPh2py)]BF4, 2c,5a
was the only product obtained.
Complexes with one intramolecular hydrogen bond
were synthesized by the protonation of 1a-c with HBF4.
In these reactions derivatives of formula [Ru(arene)Cl2-
(κ1-PNH)]BF4 (PNH ) dpimH, arene ) p-cymene, 4a;
C6H6, 4b; PNH ) PPh2pyH, arene ) p-cymene, 4c) were
obtained and characterized as complexes with NH‚‚‚Cl2
hydrogen bonds (see structural discussion). It was
verified that 4a, in the presence of methanol, also
evolves to 3a, albeit at a slower rate than when 1a is
the starting material.
these complexes, but not from the rest, supports the
different structural location of this group in 3a, 3b, and
3d (an N-coordinated ligand).
Structural information concerning the presence of the
ligands and counteranions in the different complexes
was obtained from the IR spectra (see Experimental
Section).
The 31P NMR spectra are informative in terms of the
coordination mode of the phosphine. A deshielding effect
is observed in all of the complexes in the chemical shift
of the dpim phosphorus signal when compared to that
of the free ligand. The coordination-induced shifts (CIS)
for the neutral complexes 1a,b are relatively low. The
same trend has been observed for 1c.5a This situation
can be ascribed to the relative instability of the LUMO
in pyramidal 16-electron two-legged piano stools.23 This
observation is also probably related with the reported
stability of 16-electron [RuX2(arene)] complexes where
X2 are π-donor ligands such as chalcogenates24 or
diimino groups.25 A comparably low CIS is also observed
for the cationic derivatives 4a-c. The expected shielding
to high field of the P resonance is observed when, in
comparable complexes, the phosphine changes from the
κ1-P to the κ2-PN coordination mode as a consequence
of the formation of a four-membered chelate ring.26
Complexes 3a, 3b, and 3d show 31P resonances at
very low field, and this is a consequence of the phos-
phinite nature of the ligand after P-C bond activation.
The chemical shifts are consistent with those observed
for similar complexes.16c,d Although there are exceptions,
it is usually the case that the replacement of p-cymene
by C6H6 induces a relative shift to low field in the
P-chemical shift, probably as a consequence of the more
pronounced electron-donor character of the former
group.
Structural Characterization. The FAB MS experi-
ments (1-3 complexes) showed molecular peaks that
-
correspond to the loss of anions such as Cl- (1a,b), BF4
-
(2a,b and 3a,b), or BPh4 (3d) from the mononuclear
molecular mass. Peaks arising from the additional loss
of the arene fragment were also observed. Complexes
3a, 3b, and 3d exhibited base peaks revealing the loss
of methylimidazole. The easy loss of this fragment from
(16) Illustrative examples are: (a) Vierling, P.; Riess, J. G. J. Am.
Chem. Soc. 1981, 103, 2466. (b) Van Leeuwen, P. W. N. M.; Roobeek,
C. F. Organometallics 1990, 9, 2179. (c) Nakazawa, H.; Yamaguchi,
Y.; Mizuta, T.; Ichimura, S.; Miyoshi, K. Organometallics 1995, 14,
4635. (d) Crochet, P.; Demerseman, B.; Rocaboy, Ch.; Scheleyer, D.
Organometallics 1996, 15, 3048. (e) Yang, K.; Bott, S. G.; Richmond,
M. G. Organometallics 1996, 15, 4480. (f) Geldbach, T. J.; Pregosin,
P. Eur. J. Inorg. Chem. 2002, 1907.
The 1H and 13C NMR spectra of these complexes are
also conclusive. The resonance assignments were made
on the basis of 1H-1H COSY, NOESY, and 1H-13C
COSY experiments. The p-cymene ligand is particularly
informative with respect to the symmetry of the three-
legged fragment ML3 for complexes 1a-4a and 4c.
(17) Trost, B. M.; Murphy, D. J. Organometallics 1985, 4, 1143.
(18) Pino, P.; Consiglio, G. Pure Appl. Chem. 1983, 55, 1781.
(19) Mutez, S.; Mortreux, A.; Petit, F. Tetrahedron Lett. 1988, 29,
1911.
(20) Potier, Y.; Mortreux, A.; Petit, F. J. Organomet. Chem. 1989,
370, 333.
(23) Hofmann, P. Angew. Chem., Int. Ed. Engl. 1977, 16, 536.
(24) Mashima, K.; Kaneko, S.; Tani, K.; Kaneyoshi, H.; Nakamura,
A. J. Organomet. Chem. 1997, 545-546, 345.
(21) Hatat, C.; Karim, A.; Kokel, N.; Mortreux, A.; Petit, F.
Tetrahedron Lett. 1988, 29, 3675.
(25) Haack, K.-J.; Hashiguehi, S.; Fujii, A.; Ikariya, T.; Noyori, R.
Angew Chem., Int. Ed. Engl. 1997, 36, 285.
(22) Karim, A.; Mortreux, A.; Petit, F. J. Organomet. Chem. 1986,
312, 375.
(26) Garrow, P. E. Chem. Rev. 1981, 81, 229.

Ruthenium Arene Derivatives
Organometallics, Vol. 23, No. 24, 2004 5697
Scheme 2
Complexes 1a, 4a, and 4c, which contain a Cs ML2L′
fragment, show two different aromatic CH groups in
1
both the H and 13C NMR spectra. Only one type of
isopropylic methyl group is observed. In contrast, com-
plexes 2a and 3a show four different aromatic CH
groups and diastereotopic isopropylic methyl groups as
a consequence of the chirality of the Ru center due to
the asymmetry (C1) of the MLL′L′′ three-legged frag-
ment.
Evidence for restricted rotation of the p-cymene ligand
1
but not for the benzene group is provided by the H
NMR spectra of several complexes. For example, a
detailed analysis of the aromatic CH resonances for 1a
shows the existence of a selective JHP coupling of 1.6
Hz between P and protons 2 or 6, which are situated
near the Me substituent (for numbering scheme, see
Scheme 1). This selective coupling constant has been
observed in complexes bearing tethered η1-P:η6-arene-
(CH2)3PPh2 ligands27 where the arene rotation is clearly
precluded. In the case of complex 2a, a broadening of
the resonances of these protons is observed, and this
disappears when 31P is irradiated. This phenomenon
could also indicate a restricted rotation of the arene. A
smaller JHP coupling (0.7-1 Hz) is observed for the
corresponding benzene derivatives 1b and 2b, which
suggests an averaged constant owing to free arene
rotation.
For the whole set of complexes, the imidazole and
pyridine fragments show the expected resonances, but
these are sometimes partially obscured by the aromatic
Ph proton or carbon signals. In contrast with the rest
of the complexes, the imidazole ligand in 3a, 3b, and
3d shows the supplementary CH2′ resonance as a singlet
at low field. These complexes also show a doublet at
about 3.5 (1H) and 56 (13C) ppm (JHP ≈ 11 Hz; JCP ≈ 13
Hz) due to the MeO fragment of the phosphinite ligand,
a situation in agreement with the literature data.16c,d,f
As stated previously, complexes 4a-c give NMR
spectra that are consistent with a Cs symmetry. Vari-
able-temperature 1H NMR spectra recorded for 4c both
in acetone-d6 and in chloroform-d show that this sym-
metry remains over the temperature range studied (i.e.,
the limits of the solvent liquid state). A broad singlet is
observed at low field, and this is assigned to the
H-N(heterocycle) group (MeIm, 4a,b, or py, 4c). In the
variable-temperature experiments carried out on 4c,
changes in the chemical shift of the NH resonance were
not observed in chloroform-d or acetone-d6. When the
temperature was increased, this resonance slightly
broadened in chloroform-d, while in acetone-d6 solutions
the broadening was very pronounced until the signal
nearly disappeared into the baseline. This behavior is
indicative of an incipient proton exchange without
reaching the fast rate regime. The approximate activa-
tion energies were calculated from the width at half-
height of the resonances resulting to be 35 kJ/mol in
chloroform-d and 21 kJ/mol in acetone-d6. A dilution
1/20 (v/v) of the acetone solution had no significant
influence on the broadening of the resonance. However,
the stated decrease of the energy barrier in acetone is
indicative of its participation in the process. This
behavior can be interpreted in terms of a rapid intra-
molecular exchange of the proton between the NH and
the two chloride groups, favored by the presence of
solvents such as acetone with protonation ability. A
support of this proposal is the finding of a N-H‚‚‚Cl2
hydrogen bond in the solid state for complexes 4a and
4b (see below).
Mechanistic Considerations for the P-C Activa-
tion of dpim. As depicted in eq 1, the classical
mechanism for the P-C activation of aryl phosphines
is thought to require the prior formation of an unsatur-
ated precursor (16e) that is in equilibrium with a
saturated phosphido compound (18e). It is this latter
species that undergoes the nucleophilic attack by the
incoming nucleophile (Nu). The spontaneous oxidative
addition of a P-C bond in unsaturated phosphino
derivatives is considered a reversible16a and feasible28
process, albeit with a high energy cost.
The mild conditions found in the activation of the
dpim phosphine in complexes 1a,b suggest the existence
of an alternative mechanism where less harsh condi-
tions are required. Recently, Pregosin reported interest-
ing examples of P-C activation under mild conditions,
and these have been reviewed.16f In these studies the
P-C bond cleavage is induced by the addition of either
an acid29 or the solvent.30
Experiments aimed at obtaining information about
the possible mechanism of this reaction in our complexes
initially involved monitoring the 1H NMR spectra dur-
ing the transformation of the initial compound. In the
first set of experiments, which used 1a or 2a as starting
materials, the amount weighed was the same (4 mg in
0.45 mL of deuterated solvent(s), methanol-d4, chloro-
form-d, or mixtures of these). The monitoring time was
approximately 12 h. In the first studies a methanol-d4/
chloroform-d ratio of 3.5:1 (v/v) was used. In other
experiments this ratio was changed in order to gain
further insight into the effect of changing the amount
of methanol-d4. This process is outlined in Scheme 2,
and it is useful to refer to this scheme in the next
discussion. The following general observations were
made: (i) 1a or 2a transforms to give the corresponding
(28) Cowley, A. H.; Kemp, R. A. Chem. Rev. 1985, 85, 367.
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1998, 17, 5213. (b) der Reijer, C. J.; Wo¨rle, M.; Pregosin, P. S.
Organometallics 1998, 19, 309. (c) Geldbach, T. J.; Pregosin, P. S. Inorg.
Chim. Acta 2002, 330, 155.
(30) (a) Geldbach, T. J.; Drago, D.; Pregosin, P. S. Chem. Commun.
2000, 1629. (b) Geldbach, T. J.; Drago, D.; Pregosin, P. S.; Bassetti,
M. Organometallics 2001, 20, 2990.
(27) Ghebreyessus, K. Y.; Nelson, J. H. Organometallics 2000, 19,
3387.

5698 Organometallics, Vol. 23, No. 24, 2004
Caballero et al.
Figure 1. Plot of the transformation of 1a to give 2e and 3e at 25 °C. The data were obtained from the relative intensity
of the Me-Im groups in the 1H NMR spectra. A solution of 4 mg of 1a in a methanol-d4/chloroform-d ratio of 3.5 mL/1 mL
was used.
The mechanism depicted in Scheme 2 is reasonably
consistent with all these observations. The solvate
derivative 5 is included in order to account for the need
for MeOH in the transformation of 1a to 2e. The
aforementioned inhibition by chlorides on the formation
of 3e and 2e from 1a shows that 5 is a reasonable
intermediate in the transformation of 1a and 2e into
the phosphinite 3e. In this way, 5 could be obtained
from 1a by methanolysis of the Ru-Cl bond. The ability
of methanol to eliminate chlorides in solvolysis reactions
is well documented,31 and the stability of 1a in chloro-
form supports this proposal. The solvate intermediate
5 is shown in Scheme 2 with an OH‚‚‚N bridge, which
seems reasonable considering the ease of formation of
Figure 2. Plot showing the time dependence of the
hydrogen bonds in 4a-c. A marked shift in the equi-
formation of 3e from 1a in deuterated solvents of different
librium of 1a and 2e with 5 toward the former com-
compositions at 25 °C. The data were obtained from the
pounds must exist, since 5 is not observed in any of the
spectra. Consequently, it is possible to conclude that k-1
> k1 and k2 > k-2. The ratio k1 > k-2 is deduced from
the different rates of transformation of 1a and 2b to
give 3e.
relative intensity of the Me-Im groups in the 1H NMR
spectra. A solution of 4 mg of 1a was used in each
experiment.
cation of 3. Complex 2e (the same complex as 2a but
with Cl- as a counteranion) is formed more quickly from
1a than 3e (the same complex as 3a but with Cl- as a
counteranion). The evolution of this transformation with
time, starting from 1a, is illustrated in Figure 1. (ii) The
formation of 1a from 2a was not observed, and this is
clearly a consequence of the absence of Cl-. (iii) The
formation of 3a or 3e is irreversible. (iv) The rate of
formation of 2e and 3e from 1a is enhanced when the
amount of methanol-d4 is increased in the mixture of
deuterated solvents. For instance, with methanol/
chloroform ratios of 3.5:1 and 1:3.5 the formation of 3e
follows the curves depicted in Figure 2. (v) The forma-
tion of 3e or 2e from 1a is inhibited by the addition of
chlorides (10 equiv of LiCl). (vi) When chlorides were
added to the solution of 2a (LiCl, 6.33 equiv), compounds
1a and 2e equilibrate in approximately 1 h. After this
time 3e is present in a very small amount in the spectra
(see Figure 3). The equilibrium constant for the process
2e + Cl- T 1a was found to be 11.21 mol-1. (vii) An
additional observation is that 1a is not transformed into
2e or 3e in chloroform-d in the absence of methanol-d4,
and (viii) the free phosphine is unaffected in pure
chloroform-d or methanol-d4.
The irreversible transformation step of 5 into 3e can
be understood in terms of an intramolecular electro-
philic attack of the acid proton of the methanol onto the
N3 of the imidazole, followed by nucleophilic attack of
the methanolate fragment (i1 in Scheme 3). This step,
which is probably concerted, is supported by the experi-
mental observation that 4a is able to give the phos-
phinite 3a in methanol but at a slower rate than from
1a. The transition state proposed in Scheme 3 is
reminiscent of a bridging imidazolium ion, which prob-
ably evolves to a C-coordinated carbene fragment (i2)
that quickly tautomerizes to the N-coordinated imida-
zole group on 3e.
The 1,2 shift and tautomerization of the imidazole
fragment probably makes the P-MeIm activation ir-
reversible. This irreversibility of the P-C cleavage
induced by solvolysis has previously been observed in
a few other examples.16d,30a
As stated above, the chemical behavior of dpim and
PPh2py contrasts sharply as far as the P-C activation
(31) Arena, C. G.; Calamia, S.; Faraone, F.; Graiff, C.; Tiripicchio,
A. J. Chem. Soc., Dalton Trans. 2000, 3149.

Ruthenium Arene Derivatives
Organometallics, Vol. 23, No. 24, 2004 5699
Figure 3. Plot of the transformation of 2a into 1a and 3e in the presence of chlorides at 25 °C. A solution of 4 mg of 2a
and 1.6 mg of LiCl in a mixture of methanol-d4/chloroform-d (0.350 µL/0.100 µL) was used.
Table 1. Variations of the Initial Rate vs the
Initial Concentration of 2a
Scheme 3
[2a] × 104 M
2.5
5
10
15
vi × 108 (mol L-1 s-1
)
2.52
3.78
7.86
11.3
MeOH, an initial concentration of 1a of 3.5 × 10-4
M
at 25 °C was used with MeOH concentrations of 18.5
and 12.33 M. In this case initial rates of 2.63 × 10-7
and 1.77 × 10-7 L mol-1 s-1 were obtained, respectively.
These values also showed first order with respect to
MeOH. Therefore, the disappearance rate of 1a may be
expressed as
-d[1a]/dt ) kexp[1a][MeOH ]
(2)
The average value for the second-order rate constant
kexp was found to be 4.15 × 10-5 L mol-1 s-1. On the
basis of the data obtained and the mechanism proposed
in Scheme 2, this value must correspond to k1.
The rate constant k-2 was obtained by measuring the
initial rates for the decay of 2a in methanol (22.2 M) at
25 °C with different initial concentrations of this
complex (see Table 1).
step is concerned, probably due to the carbenic character
that the imidazole group has in its quaternized state.
In this carbenic form, MeImH+ can be considered a good
leaving group and, as a consequence, the nucleophilic
attack of MeO- on the P atom is promoted.
To support the existence of the mechanism proposed
in Scheme 2 and to extract all the possible parameters
from this mechanism, a number of spectroscopic experi-
ments were carried out. Initially, the rate constants k1
and k-2 were determined spectrophotometrically by
following the initial decay of 1a and 2a in methanol. A
spectrophotometric technique was used to obtain this
value due to the impossibility of following the initial
decays of 1a and 2a in methanol using NMR techniques.
The rate constant k1 was obtained by applying the
initial rates method to the decay of 1a in methanol, thus
minimizing the importance of the reverse reaction (-1).
For the decay of 1a at 25 °C and with [MeOH] ) 18.5
M, the initial rates obtained for the initial concentra-
tions of 1a, 6 × 10-4 and 3.5 × 10-4 M, were 4.76 ×
10-7 and 2.63 × 10-7 L mol-1 s-1, respectively. The
results show a first kinetic order with respect to 1a. In
an effort to estimate the reaction order with respect to
The plot of vi vs [2a] gave a straight line (rxy ) 0.998)
with a positive slope (kexp ) 7.44 × 10-5 s-1) and
ap
negligible intercept; this is indicative of a first order
with respect to species 2a. A first order with respect to
MeOH was also obtained. At an initial 2a concentration
of 5 × 10-4 M in methanol (22.2 and 18.5 M) at 25 °C,
the respective initial rates were 3.78 × 10-8 and 3.18
× 10-8 L mol-1 s-1, respectively. Therefore, the experi-
mental rate law may be expressed as follows
vi ) -d[2a]/dt ) kexp[2a][MeOH]
(3)
where kexp was found to be 3.35 × 10-6 L mol-1 s-1. On
the basis of the data obtained and the mechanism
proposed in Scheme 2, this value must correspond to

5700 Organometallics, Vol. 23, No. 24, 2004
Caballero et al.
Figure 4. ORTEP view with atom numbering of complex
1a (30% probability ellipsoids).
k-2. From the decay of 2a in the presence of chlorides
(Figure 3) the concentrations of 1a and 2a are constant
over a long time interval, and therefore, the equilibrium
approximation can be used. For this interval of time the
concentration of 3a varies linearly with time. This
observation is expected given the mechanism proposed
(Scheme 2) and considering that the concentration of 5
must be constant when 1a and 2a reach the equilibrium.
Figure 5. ORTEP view with atom numbering of complex
1b (30% probability ellipsoids).
d[3a]
dt
) k3[5]e
(4)
The concentration of 5 may be calculated from the
equilibria between 1a T 5 and between 2a T 5 (Scheme
2). Thus eq 4 is reduced to eq 5.
k3k1[1a]e[MeOH]e k3k-2[2a]e[MeOH]e
d[3a]
dt
)
)
(5)
k-1[Cl-]e
k2
The slope of the plot [3a] vs t, d[3a]/dt, was 1.81 ×
10-8 mol L-1 s-1. By inserting the values of [1a]e )
0.00634 M, [2a]e ) 0.00707 M, [MeOH]e ) 24.7 M, and
[Cl-]e ) 0.0801 M in eq 5 and taking into account the
values of k1 and k-2 above cited, the following relations
Figure 6. ORTEP view with atom numbering of the cation
of complex 4a (30% probability ellipsoids).
were obtained: k-1 ) 4491k3, k2 ) 32.4k3, and k-1
139k2.
)
Moreover, the global equilibrium constant, corre-
sponding to the steps (1) and (2) of the Scheme 2, can
be obtained as follows.
[1a]e
[2a]e[Cl-]e
k-2k-1
k2k1
K )
)
) 11.21 L mol-1 (6)
X-ray Molecular Structures of 1a‚1/2CH2Cl2, 1b‚
2CH2Cl2, 4a‚CH2Cl2, and 4b. The molecular structures
of the title complexes (see Figures 4-7) were determined
by X-ray diffraction. The crystallographic data and a
selection of bond distances and angles are given in
Tables 2 and 3, respectively. The structures are es-
sentially very similar as far as the molecular backbone
is concerned. The arene ruthenium fragment is linked
to two chlorides and a phosphine to give a three-legged
piano-stool structure. In 4a,b the dpim ligand is proto-
nated and the BF4- counteranion is also present. Bond
Figure 7. ORTEP view with atom numbering of complex
4b (30% probability ellipsoids).
lengths and angles are in the range of those found in
other X-ray structures of [Ru(arene)Cl2(phosphine)]
compounds.5a,27,32,33 Ru-arene bond lengths are also in
the range found for other arene structures. A hetero-

Ruthenium Arene Derivatives
Organometallics, Vol. 23, No. 24, 2004 5701
Table 2. Crystal Data and Structure Refinement for 1a‚1/2CH2Cl2, 1b‚2CH2Cl2, 4a‚CH2Cl2, and 4b
1a‚1/2CH2Cl2
1b‚2CH2Cl2
4a‚CH2Cl2
4b
empirical formula
fw
C
26.50H30Cl3N2PRu
C24H25Cl6N2PRu
686.20
C27H32BCl4F4N2PRu
745.20
C22H22BCl2F4N2PRu
604.17
614.91
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
173(2)
0.71073
298(2)
173(2)
173(2)
0.71073
monoclinic
C2/c
36.913(2)
36.913(2)
24.961(1)
90
127.409(1)
90
5629.2(5)
8, 1.619
0.1201
2752
0.71073
0.71073
monoclinic
P2(1)/n
10.180(6)
13.035(7)
17.884(10)
90
monoclinic
P2/n
14.1253(9)
10.7073(7)
17.442(1)
90
96.701(1)
90
2620.0(3)
4, 1.559
monoclinic
P2(1)/n
12.661(2)
b (Å)
16.226(3)
c (Å)
15.069(3)
R (deg)
90
â (deg)
92.015(3)
94.892(12)
90
γ (deg)
90
volume (Å3)
Z, calcd density (g/cm3)
3093.9(9)
2364(2)
4, 1.600
4, 1.697
absorp coeff (cm-1
F(000)
)
0.0984
1252
0.0950
0.1002
1504
1208
cryst size (mm)
limiting indices
0.50 × 0.41 × 0.10
-18 e h e 18,
-14 e k e 14,
-23 e l e 13
17 872/6517
0.0522/0/424
0.945
0.35 × 0.10 × 0.10
-31 e h e 45,
-9 e k e 9,
-30 e l e 28
16 289/5527
0.0579/0/307
0.961
0.32 × 0.28 × 0.15
-15 e h e 15,
-20 e k e 8,
-18 e l e 18
16 306/6131
0.0545/0/361
1.083
0.16 × 0.10 × 0.10
-12 e h e 12,
-16 e k e 16,
-22 e l e 16
13 584/4842
0.0657/0/386
0.976
no. of reflns collected/unique
Rint/restraints/params
goodness-of-fit on F2
final R indices [I>2σ(I)]a
R1 ) 0.0348,
wR2 ) 0.0678
R1 ) 0.0593,
wR2 ) 0.0753
0.0383, 0
R1 ) 0.0407,
wR2 ) 0.0884
R1 ) 0.0733,
wR2 ) 0.0992
0.0519, 0
R1 ) 0.0451,
wR2 ) 0.1117
R1 ) 0.0845,
wR2 ) 0.1384
0.0665, 0
R1 ) 0.0397,
wR2 ) 0.0648
R1 ) 0.0784,
wR2 ) 0.0743
0.0224, 0
R indices (all data)a
weightsb (a,b)
largest diff peak and hole (e‚Å-3
)
0.798 and -0.686
0.628 and -0.592
0.875 and -0.971
0.465 and -0.455
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑[w(Fo2 - Fc )2]/∑[w(Fo2)2]]0.5
.
b The weighting scheme employed was w ) [σ2(Fo)2 + (aP)2+ bP]] and
2
2
2
P ) (|Fo| + 2|Fc| )/3.
Table 3. Selected Bond Distances (Å) and Bond Angles (deg) of Complexes 1a‚1/2CH2Cl2, 1b‚2CH2Cl2,
4a‚CH2Cl2, and 4b
1a‚1/2CH2Cl2
1b‚2CH2Cl2
4a‚CH2Cl2
4b
Ru(1)-Cl(1)
2.4070(7)
2.4320(7)
2.3523(7)
2.243(3)
2.243(3)
2.225(3)
2.218(3)
2.161(3)
2.193(3)
92.10(2)
87.99(2)
85.32(2)
2.4055(10)
2.4085(11)
2.3529(10)
2.180(4)
2.260(4)
2.245(4)
2.195(5)
2.164(4)
2.172(4)
87.10(4)
87.84(4)
90.13(4)
2.3982(13)
2.4221(15)
2.3404(14)
2.159(5)
2.174(5)
2.219(4)
2.220(5)
2.175(5)
2.177(5)
87.08(5)
87.70(5)
90.96(4)
3.2314(4)
3.0093(5)
2.8809(5)
2.2843(4)
0.881(1)
139.64(1)
105.65(1)
2.3982(13)
2.4221(15)
2.3404(14)
2.159(5)
Ru(1)-Cl(2)
Ru(1)-P(1)
Ru(1)-C(1)
Ru(1)-C(2)
2.174(5)
Ru(1)-C(3)
2.219(4)
Ru(1)-C(4)
2.220(5)
Ru(1)-C(5)
2.175(5)
Ru(1)-C(6)
2.177(5)
Cl(1)-Ru(1)-Cl(2)
P(1)-Ru(1)-Cl(1)
P(1)-Ru(1)-Cl(2)
N(1)-Cl(2)
87.08(5)
87.70(5)
90.96(4)
3.0521(16)
3.1714(12)
2.2120(11)
2.8571(11)
0.9062(5)
101.97(3)
153.83(5)
N(1)-Cl(1)
H(1A)-Cl(2)
H(1A)-Cl(1)
N(1)-H(1A)
N(1)-H(1A)-Cl(1)
N(1)-H(1A)-Cl(2)
geneous distribution of the Ru-C(arene) bond distances
was observed in the sense that distances trans to the
more strongly donating phosphine group are longer that
those trans to the chlorine atoms. This observation has
been discussed elsewhere,34 and it seems to be a
consequence of the different donor character of the
ligands in the legs of the piano stool. For the neutral
complexes 1a and 1b, the phosphine conformation
around the Ru-P axis means that one of the phenyl
groups is located in an anti orientation with respect to
the arene moiety. In contrast, in the structure of the
cations of 4a,b, the MeIm group replaces the aforemen-
tioned phenyl in this position. This apparently fortuitous
arrangement is very probably linked with one of the
most important features of these structures, namely, the
existence of a strong hydrogen bond. The bridging
proton is clearly centered in the MeIm group with a
short N(1)-H(1A) distance of 0.88 Å. This functional
group points toward the two chlorine groups with two
short H(1A)-Cl bond distances of 2.881 (Cl(2)) and 2.285
(Cl(1)) Å (4a) and 2.212 (Cl(2)) and 2.857 (Cl(1)) Å (4b).
In each complex both bond lengths are shorter than the
corresponding sum of van der Waals’ radii, which is
(32) (a) Bennett, M. A.; Robertson, G. B.; Smith, A. K. J. Organomet.
Chem. 1972, 43, C41. (b) Yamamoto, Y.; Sato, R.; Matsuo, F.; Sudoh,
C.; Igoshi, T. Inorg. Chem. 1996, 35, 2329.
(33) (a) Therrier, B.; Ward, T. R.; Pilkington, M.; Hoffmann, C.;
Giraldoni, F.; Weber, J. Organometallics 1998, 17, 330. (b) Therrier,
B.; Ward, T. R. Organometallics 1999, 18, 1565.
(34) (a) Siedle, A. R.; Newmark, R. A.; Pignolet, L. H.; Wang, D. X.;
Albright, T. A. Organometallics 1986, 5, 38. (b) Ghebreyessus, K.;
Nelson, J. H. J. Organomet. Chem. 2003, 669, 48.

5702 Organometallics, Vol. 23, No. 24, 2004
Caballero et al.
Table 4. Results of the Catalytic Tests for the
Table 5. Results of the Catalytic Tests of
Hydrogenation of Cyclohexanone with 2-Propanola
Hydrogenation of Phenylacetylene with Molecular
Hydrogena
PhCHdCH2
styrene (St)
H2
8
H2
8
PhCH2CH3
ethylbenzene (Eb)
PhCtCH
phenylacetylene
b
TOF (h-1
)
yield (%)b conv conv
b
catalyst
TOF (h-1
)
yield (%)b
S:cat.
KOH/cat.
catalyst [(St)/(Eb)] [(St)/(Eb)] (%)b (%)c S:cat. solvent
1a
1a
2a
2a
182
418
2.5
54
9.1
21
2000:1
2000:1
500:1
1a
2a
2a
217/53
195/141
199/72
21.7/5.3
19.5/14.1 33.6 35.0 1000:1 CH2Cl2
19.9/7.2 27.1 39.4 1000:1 i-PrOH
27
59.6 1000:1 CH2Cl2
333:1
100:1
0.5
13.5
500:1
a The reaction was carried out at 80 °C with 30 atm of H2. See
also Experimental Section. b These parameters were determined
after 1 h of reaction. c Determined after 16 h of reaction.
a The reaction was carried out at reflux temperature. See
Experimental Section for more details. b These parameters were
determined after 1 h of reaction.
noteworthy result if we take into account that most
catalysts are inactive under these circumstances. In fact,
2a is almost inactive in the absence of added base, since
it exhibits a negligible activity (TOF ) 2.5). As expected,
the results are better for both precatalysts in the
presence of an external base. The differences between
1a and 2a are probably related to the coordination mode
of the phosphine. We can envisage that the free imida-
zolyl nitrogen in 1a plays, in some way, the role of the
base in the accepted mechanism. The bidentate coordi-
nation mode of the phosphine in 2a prevents the
imidazolyl nitrogen from playing the same role.
We also tested the catalytic activity of 1a and 2a in
the hydrogenation of phenylacetylene with molecular
hydrogen (see Table 5). These experiments were per-
formed without the addition of base. On using both
precursors, the predominant product is styrene at the
beginning of the reaction, but ethylbenzene is also
detected. The relative amount of ethylbenzene increases
with time. This fact means that, in both cases, not only
is the triple bond of the phenylacetylene hydrogenated,
but also the double bond of the resulting styrene.
The cationic complex 2a shows a better activity than
1a, which is in agreement with the results obtained by
Moldes and co-workers for the analogous arene Ru(II)
complexes derived from PPh2Py.5a Apparently, in this
case, the noncoordinated nitrogen does not have a
positive effect. This is in accordance with a mechanism
implying the homolytic activation of the molecular
hydrogen. Finally, the presence of a solvent such as
2-propanol decreases the catalytic activity, as can be
seen from the comparison of the results for 2a.
estimated to be 3.0 Å. This implies the existence of an
asymmetric and bifurcated hydrogen bond. In this
bridge, the smaller distance is very short when com-
pared with reported hydrogen bonds involving an
NH‚‚‚Cl interaction in Ru or Ir complexes.35 In 4a, the
Cl(1)-N(1) distance of 3.01 Å, which is shorter than the
Cl(2)-N(1) bond (3.23 Å), confirms the previous state-
ment regarding the existence of an asymmetric and
bifurcated hydrogen bond. Similarly, in 4b the two
Cl-N distances are short but different. In our opinion
this is a consequence of a very efficient location and
orientation of the MeImH group, which favors such
types of bonds.
Catalytic Behavior of Compounds 1a and 2a in
Hydrogenation Processes. According to the litera-
ture, arene Ru(II) complexes are good precursors for
catalytic hydrogenation processes.5a,8a,b,25,34b,36,37 We
therefore carried out preliminary tests on the catalytic
activity of complexes 1a and 2a both in transfer
hydrogenation and in hydrogenation with molecular
hydrogen. These preliminary results are given in Tables
4 and 5.
First, we found that 1a is active in the transfer
hydrogenation (see Table 4) of cyclohexanone using
2-propanol as the hydrogen donor, even in the absence
of an external base. The TOF is 182, which is a
(35) (a) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem.
Soc. 1987, 109, 2803. (b) Clark, G. R.; Hodgson, D. J.; Ng, M. M. P.;
Rickard, C. E. F.; Roper, W. R.; Wright, L. J. Chem. Commun. 1988,
1552. (c) Fryzuk, M. D.; Montgomery, C. D.; Rettig, S. J. Organome-
tallics 1991, 10, 467. (d) Redmore, S. M.; Rickard, C. E. F.; Webb, S.;
Wright, L. J. Inorg. Chem. 1997, 36, 4743. (e) Durran, S. E.; Smith,
M. B.; Slawin, A. M. Z.; Steed, J. W. J. Chem. Soc., Dalton Trans. 2000,
2771. (f) Velders, A. H.; Ugozzoli, F.; Biagini-Cingi, M.; Manotti-
Lanfredi, A. M.; Haasnoot, J. G.; Jan Reed, K. J. Eur. J. Inorg. Chem.
1999, 213. (g) Dutta, S.; Bhattacharya, P. K.; Horn, E.; Tiekink, E. R.
T. Polyhedron 2001, 15-16, 1815.
We would like to emphasize that these are prelimi-
nary catalytic tests and that the reaction conditions
were not optimized. Although the conversions are rather
low, it is noteworthy that the substrate:catalyst ratio
used in our experiments is clearly high (2000:1, 1000:
1, or 500:1), especially when compared with the more
common ratios used of 200, 100, or even 15 (see for
example, refs 5a, 34b, 37k,l).
(36) (a) Rath, R. K.; Nethaji, M.; Chakravarty, A. R. Polyhedron
2001, 20, 2735. (b) Polborn, K.; Severin, K. Chem. Eur. J. 2000, 6,
4604.
(37) (a) Hashiguchi, S.; Fujii, A.; Takehara, J.; Ikariya, T.; Noyori,
R. J. Am. Chem. Soc. 1995, 117, 7562. (b) Fujii, A.; Hashiguchi, S.;
Uematsu, N.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1996, 118, 2521.
(c) Matsumura, K.; Hashiguchi, S.; Ikariya, T.; Noyori, R. J. Am. Chem.
Soc. 1997, 119, 8738. (d) Takehara, J.; Hashiguchi, S.; Fujii, A.; Shin-
ichi, I.; Ikariya, T.; Noyori, R. Chem. Commun. 1996, 233. (e) Noyori,
R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97. (f) Yamakawa, M.;
Ito, H.; Noyori, R. J. Am. Chem. Soc. 2000, 122, 1466. (g) Palmer, M.
J.; Walsgrove, T.; Wills, M. J. Org. Chem. 1997, 62, 5226. (h) Alonso,
D. A.; Brandt, P.; Nordin, S. J. M.; Andersson, P. G. J. Am. Chem.
Soc. 1999, 121, 9580. (i) Petra, D. G. I.; Kamer, P. C. J.; van Leeuven,
P. W. M. N.; Goubitz, K.; Van Loon, A. M.; de Vries, J. G.; Schoemaker,
H. E. Eur. J. Inorg. Chem. 1999, 2335. (j) Schwink, L.; Ireland, T.;
Pu¨ntener, K.; Knochel, P. Tetrahedron: Asymmetry 1998, 9, 1143. (k)
Everaere, K.; Mortreux, A.; Bulliard, M.; Brussee, J.; van der Gen, A.;
Nowogrocki, G.; Carpentier, J. F. Eur. J. Org. Chem. 2001, 275. (l)
Pasto´, M.; Riera, A.; Perica`s, M. A. Eur. J. Org. Chem. 2002, 2337.
Conclusions
We have prepared and characterized new arene
ruthenium(II) complexes containing the potentially
hemilabile ligand 2-(diphenylphosphino)-1-methylimi-
dazole (dpim). In some cases, the behavior has been
compared with that of complexes containing the similar
ligand, 2-(diphenylphosphino)pyridine (PPh2py). The
transformation of the neutral derivatives of the type
[RuCl2(arene)(κ1-PN)] into the cationic species [RuCl-

Ruthenium Arene Derivatives
Organometallics, Vol. 23, No. 24, 2004 5703
(arene)(κ2-PN)]X was achieved despite the fact that the
metallacycle formed in the case of the dpim ligand would
be expected to have considerable strain. Protonation of
the neutral derivatives with HBF4 led to the complexes
[RuCl2(arene)(κ1-PNH)]BF4, which exhibit a hydrogen
bond. The neutral, cationic and protonated complexes
containing the dpim ligand react with methanol to give
the derivatives [RuCl(arene)(HImMe){PPh2(OMe)}]BF4
(Im ) imidazolyl). In these complexes an unexpected
activation of the phosphine ligand is observed and this
implies that cleavage of the P-C(ImMe) bond has taken
place. Such a process leads to the formation of a
phosphinite ligand under very mild conditions. We
believe that this reaction can be applied to other alcohols
including commercially available chiral examples. The
derivatives containing the PPh2py ligand do not undergo
this transformation. Proposals concerning the mecha-
nism of the transformation and the different behavior
of the two ligands are presented. Several derivatives
have been characterized by X-ray diffraction studies,
and these show a three-legged piano-stool structure. The
complexes [RuCl2(arene)(κ1-PNH)]BF4 exhibit a bifur-
cated and asymmetric hydrogen bond, NH‚‚‚Cl2, in the
solid state. The protonation process determines the
disposition of the imidazolyl group in the dpim ligand.
Preliminary catalytic tests involving hydrogenation
have been performed. It is concluded that probably the
pendant imidazolyl nitrogen in some way plays the role
of the external base in transfer hydrogenation processes,
while it does not produce a positive effect in the
hydrogenation with molecular hydrogen.
Arrhenius theory. The gas chromatographic (GC) analyses for
the reaction products of the catalytic reactions were performed
on a Hewlett-Packard 5890 with a flame ionization detector
chromatograph. Starting materials: [RuCl2(p-cymene)]2,38
[RuCl2(C6H6)]2,38 [RuCl(C6H6)(CH3CN)],15 and dpim10 were
prepared according to literature procedures. TlBF4, NaBF4,
and HBF4 were purchased from Aldrich.
X-ray Structure Determination. Data collections were
carried out on a Bruker SMART-CCD area diffractometer with
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å)
operating at 50 kV and 30 mA. A total of 1271 frames of
intensity data were collected over a hemisphere of the recipro-
cal space by combination of three exposure sets. Each frame
covered 0.3° in ω, and the first 50 frames were re-collected at
the end of data collection to monitor crystal decay. Absorption
corrections were applied using the SADABS program.39 The
structures were solved using the Bruker SHELXTL-PC soft-
ware40 by direct methods and refined by full-matrix least-
squares methods on F2. Hydrogen atoms were included in
calculated positions and refined in the riding mode, except
those bonded to nitrogen atoms, which were located on residual
density maps, then their positions fixed and refined in the
riding mode. All non-hydrogen atoms were refined anisotro-
pically. The details of the data collection and refinement are
summarized in Table 2.
Preparation of [RuCl2(p-cymene)(K1-P-dpim)] (1a). dpim
(518.4 mg, 1.95 mmol) was added over a solution of [RuCl2(p-
cymene)]2 (600 mg, 0.97 mmol) prepared in 120 mL of dichlo-
romethane. The resulting solution was stirred for 15 h at rt.
The solution was evaporated to dryness, and the resulting
residue was washed with hexane (3 × 15 mL). An orange solid
was obtained and dried under vacuum. Yield: 1.00 g (1.75
mmol, 89.4%). The compound was crystallized from CH2Cl2/
hexane, obtaining crystals of 1a‚1/2CH2Cl2 suitable for an
X-ray determination. Anal. Calcd for
C26.5H30Cl3N2PRu
(614.91): C, 51.76; H, 4.92; N, 4.56. Found: C, 51.63; H, 4.81;
N, 4.49. IR (Nujol, cm-1): 348, 288 ν(RuCl). 1H NMR (chloro-
form-d): 8.22 (m, 4H, ortho-Ph); 7.33 (m, 7H, m, para-Ph and
H4-Im); 6.95 (t, 1H, H5-Im); 5391 (dd, JHH ) 6.3, JPH ) 1.7,
2H, CH2,6-cym); 5.22 (d, JHH ) 6.3, 2H, CH3,5-cym); 3.16 (s,
3H, Me-Im); 2.50 (spt, JHH ) 7.0, 1H, CHMe2); 1.57 (s, 3H,
Me-cym); 0.92 (d, JHH ) 7.6, 6H, CHMe2) ppm. 13C NMR
(chloroform-d): 134.73 (d, JPC ) 10, 4C, ortho-Ph); 133.07 (d,
JPC ) 46.3, 2C, ipso-Ph); 130.21 (d, JPC ) 2.6, 2C, para-Ph);
128.95 (d, JPC)11.2, 1C, C2-Im); 127.81 (d, JPC)10.3, 4C, meta-
Ph); 125.33 (d, JPC ) 1.4, 2C, p-Ph); 125.36 (s, 1C, CH-Im);
125.29 (s, 1C, CH-Im); 110.34 (s, 1C, C-iPr); 94.85 (s, 1C, C-Me
cym); 92.11 (d, JPC ) 4.3, 2C, CH cym); 85.5 (d, JPC ) 6.3, 2C,
CH cym); 36.07 (s, 1C, Me-Im); 29.98 (s, 1C, CHMe2); 21.46 (s,
2C, CHMe2); 16.8 (s, 1C, Me-cym) ppm. 31P NMR (chloroform-
Experimental Section
General Methods. All manipulations were carried out
under an atmosphere of dry oxygen-free nitrogen using
standard Schlenk techniques. Solvents were distilled from the
appropriate drying agents and degassed before use. Elemental
analyses were performed with a Perkin-Elmer 2400 CHN
microanalyzer. The best analytical data were obtained for the
complexes crystallized to make the X-ray structure determina-
tions. Although in some other cases the data were totally
accurate, at least in one member of each family the agreement
of calculated and found values for carbon is (0.4%. In any case,
complexes 1-4 were obtained in enough analytic purity to be
used as starting materials. IR spectra were recorded on a
Nicolet Impact 410 spectrophotometer as KBr pellets or on a
Perkin-Elmer 883 (4000-200 cm-1 range) as Nujol mulls
deposited on a polyethylene film. FAB mass spectra (position
of the peaks in DA) were recorded with an Autospec spectrom-
eter (University of Zaragoza). NMR spectra were recorded at
room temperature (≈25 °C), unless stated otherwise, on a
d): 7.58 (s) ppm. FAB mass (m/z): 537([M - Cl]+
Cl - C10H14]+). C10H14 ) p-cymene.
); 403 ([M -
Preparation of [RuCl2(C6H6)(K1-P-dpim)] (1b). dpim
(351.5 mg, 1.32 mmol) was added over a suspension of [RuCl2-
(C6H6)(CH3CN)] (366 mg, 1.26 mmol) in 30 mL of acetonitrile.
The mixture was stirred for 3 h at rt, and an orange-brown
precipitate was formed. It was filtered and dried under
vacuum. Yield: 585 mg (1.13 mmol, 90%). Crystallization from
CH2Cl2/hexane yielded crystals of 1b‚2CH2Cl2 suitable for an
X-ray determination. Anal. Calcd for C24H25Cl6N2PRu
(686.20): C, 42.01; H, 3.67; N, 4.08. Found: C, 41.88; H, 3.75;
N, 4.00. IR (Nujol, cm-1): 297, 274 ν(RuCl). 1H NMR (chloro-
1
Varian Unity Inova-400 (400 MHz for H; 161.9 MHz for 31P;
100.6 MHz for 13C), and a Varian UNITY-300 (300 MHz for
1H; 121.4 MHz for 31P; 75.4 MHz for 13C) spectrometer. 1H
shifts were recorded using the residual proton of the solvent
as internal standard (see numbering scheme in Chart 1). All
31P shifts were referenced internally. COSY spectra: standard
pulse sequence, acquisition time 0.214 s, pulse width 10 µs,
relaxation delay 1 s, 16 scans, 512 increments. The NOE
difference spectra were recorded with 5000 Hz, acquisition
time 3.27 s, pulse width 90°, relaxation delay 4 s, and
irradiation power 5-10 dB. The probe temperature ((1 K) was
controlled by a standard unit calibrated with a methanol
reference. The value of k for the proton transfer in complex
4c was calculated on the basis of the broadening in excess of
the natural line width, W (k ) πW). The values of the
activation energy were then calculated according to the
(38) (a) Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A.
K. Inorg. Synth. 1982, 21, 74. (b) Bennett, M. A.; Smith, A. K. J. Chem.
Soc., Dalton Trans. 1974, 233.
(39) Sheldrick, G. M. SADABS. A Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Germany,
1996. Based on the method of Robert Blessing: Blessing, R. H. Acta
Crystallogr. 1995, A51, 33.
(40) Sheldrick, G. M. SHELXS-97, A Program for Solving Crystal
Structures and Crystal Structure Refinement; University of Go¨ttin-
gen: Germany, 1997.

5704 Organometallics, Vol. 23, No. 24, 2004
Caballero et al.
form-d): 8.03 (m, 4H, ortho-Ph); 7.37 (m, 6H, meta, para-Ph);
7.01 (s, 1H, CH-Im); 5.51 (d, JPH ) 0.8, 6H, C6H6); 3.2 (s, 3H,
N-Me) ppm. 13C NMR (chloroform-d): 134.38 (d, JCP ) 10.1,
4C, ortho-Ph); 131.34 (d, JCP ) 48.3, 2C, ipso-Ph); 130.78 (d,
JCP ) 2.7, 2C, para-Ph); 129.65 (d, JCP ) 12.7, 1C, C2-Im);
128.11 (d, JCP ) 10.6, 4C, meta-Ph); 125.86 (s, 1C, CH-Im);
125.84 (s, 1C, CH-Im); 89.26 (d, JPC ) 3.6, 6C, C6H6); 36.08 (s,
1C, N-Me) ppm. 31P NMR (chloroform-d): 11.85 (s) ppm. FAB
MS (m/z): 481 ([M - Cl]+); 403 ([M - Cl - C6H6]+).
3a: Anal. Calcd for C27H33BClF4N2OPRu (655.56): C, 49.47;
H, 5.07; N, 4.27. Found: C, 49.05; H, 5.14; N, 4.62. IR (KBr):
1058 νd(BF4-); 547 δd(BF4-); Nujol: 399 ν(RuCl). 1H NMR
(chloroform-d): 7.81 (s, 1H, CH2-Im); 7.61 (m, 2H, ortho-Ph);
7.49 (m, 1H, para-Ph); 7.44 (m, 2H, ortho-Ph); 7.31 (m, 1H,
para-Ph); 7.23 (m, 2H, meta-Ph); 7.15 (m, 2H, meta-Ph); 7.10
4
4
(t, 3JHH ≈ JHH ) 1.4, 1H, CH5-Im); 6.57 (t, 3JHH ≈ JHH ) 1.5,
3
1H, CH4-Im); 5.77 (dd, JHH ) 6.2, JPH ) 1.4 1H, CH-cym);
3
5.66 (d, JHH ) 6.3, 1H, CH-cym); 5.59 (dd, JHH ) 6.1, JPH
)
Preparation of [RuCl(p-cymene)(K2-PN-dpim)]BF4 (2a).
TlBF4 (66 mg, 0.23 mmol) was added to a solution of 1a (130
mg, 0.23 mmol) in 10 mL of dichloromethane. A white
precipitate was instantaneously formed. The mixture was
stirred for 3 h. An orange solution was obtained after filtration.
This was evaporated to dryness. The resulting orange powder
was washed with pentane (3 × 10 mL). Yield: 0.126 g (0.2
mmol, 87.6%). Anal. Calcd for C26H29BClF4N2PRu (623.6): C,
50.06; H, 4.67; N, 4.49. Found: C, 49.9; H, 4.68; N, 4.59. IR
(KBr, cm-1): 1058 νd(BF4); 547 δd(BF4); Nujol: 399 ν(RuCl).
1H NMR (chloroform-d): 7.88 (m, 2H, ortho-Ph); 7.63 (m, 2H,
meta-Ph; 1H, para-Ph); 7.59 (m, 1H, para-Ph); 7.49 (m, 2H,
orto-Ph; 1H, CH4-Im); 7.35 (m, 2H, meta-Ph; 1H, CH5-Im); 5.78
(d, JHH ) 6.1, 1H, CH6-cym); 5.65 (d, JHH ) 6.1, 1H, CH5-cym);
5.58 (d, JHH ) 5.8, 1H, CH3-cym); 5.10 (d, JHH ) 5.8, 1H, CH2-
1.4, 1H, CH-cym); 5.49 (d, JHH ) 6.1, 1H, CH-cym); 3.63 (d,
3JPH ) 11.3, 3H, POMe); 3.6 (s, 3H, Me-Im); 2.5 (spt, JHH
6.9, 1H, CHMe2-cym); 2.12 (s, 3H, CMe-cym); 1.13 (d, JHH
)
)
6.9, 3H, CHMe2); 1.12 (d, JHH ) 6.9, 3H, CHMe2) ppm. 13C
NMR (chloroform-d): 143.26 (d, JCP ) 1.8, 1C, CH2-Im);
3
2
4
133.35 (d, JPC ) 11.1, 2C, ortho-Ph); 132.12 (d, JPC ) 2.2,
1
1C, para-Ph); 132.1 (d, JPC ) 52.3, 1C, ipso-Ph); 131.86 (d,
2JPC ) 9.9, 2C, ortho-Ph); 131.13 (d, 4JPC ) 2.3, 1C, para-Ph);
131.05 (s, 1C, CH4-Im); 130.47 (d, JPC ) 46.5, 1C, ipso-Ph);
1
128.54 (d, 3JPC ) 10.4, 2C, meta-Ph); 128.12 (d, 3JPC ) 10, 2C,
meta-Ph); 121.24 (s, 1C, CH5-Im); 116.75 (d, JPC ) 7.3, 1C,
CiPr-cym); 103.88 (s, 1C, CMe-cym); 90.65 (d, JPC ) 4.12, 1C,
CH5-cym); 89.86 (d, JPC ) 4.22, 1C, CH3-cym); 88.9 (d, JPC
)
2.4, 1C, CH2-cym); 87.2 (s, 1C, CH6-cym); 56.79 (d, 2JPC ) 13,
1C, POMe); 34.93 (s, 1C, Me-Im); 31.01 (s, 1C, CHMe2-cym);
22.23 (s, 1C, CHMe2-cym); 22.11 (s, 1C, CHMe2-cym); 18.76
(s, 1C, CMe-cym) ppm. 31P NMR (chloroform-d): 129.7 (s) ppm.
3
cym); 3.66 (s, 3H, Me-Im); 2.62 (spt, JHH ) 6.9, 1H, CHMe2-
3
cym); 2.04 (s, 3H, Me-cym); 1.22 (d, JHH ) 6.9, 3H, CHMe2-
FAB MS (m/z): 569 ([M - BF4]+, 30%); 537 ([M - BF4
-
3
cym); 1.17 (d, JHH ) 6.9, 3H, CMe2-cym) ppm. 13C NMR
MeOH]+, 15%); 487 ([M - BF4 - MeImH]+, 100%); 451 ([M -
BF4 - MeImH - HCl]+, 55%); 421 ([M - BF4 - MeImH - Cl
- MeO]+, 55%).
(chloroform-d): 145.9 (d, 1JPC ) 52.6, 1C, C2-Im); 135.3 (d, 2JPC
4
) 11.5, 2C, ortho-Ph); 133.5 (d, JPC ) 2.8, 1C, para-Ph); 133
4
3
(d, JPC ) 2.6, 1C, para-Ph); 131.3 (d, JPC ) 11.5, 2C, meta-
Ph); 131.1 (d, 3JPC ) 14.6, 1C, CH4-Im); 130.8 (d, 3JPC ) 11.5,
2C, meta-Ph); 129.6 (d, JPC ) 11.4, 2C, ortho-Ph); 129.2 (s,
3d: Anal. Calcd for C51H53BClN2OPRu (888.31): C, 68.96;
H, 6.01; N, 3.15. Found: C, 68.51; H, 6.01; N, 3.43. IR (KBr,
cm-1): 2982, 2964, 1479, 1385, 743, 704, ν (BPh4-); Nujol: 409
ν(RuCl). 1H NMR (chloroform-d): 7.60-6.85 (m, 30H, (2 + 4)-
2
1C, CH5-Im); 128.3 (d, 1JPC ) 52.3, 1C, ipso-Ph); 121.7 (d, 1JPC
) 43.8, 1C, ipso-Ph); 107 (d, JPC ) 2.2, 1C, CH4-cym); 100.8
(d, JPC ) 1.5, 1C, CMe-cym); 89.7 (d, JPC ) 3.6, 1C, CH5-cym);
85.6 (d, JPC ) 5.6, 1C, CH6-cym); 85.3 (d, JPC ) 2.4, 1C, CH2-
cym); 84.04 (d, JPC ) 2.7, 1C, CH3-cym); 35.2 (s, 1C, Me-Im);
31.3 (s, 1C, CHMe2-cym); 23.3 (s, 1C, CHMe2-cym); 22.2 (s, 1C,
CHMe2-cym); 19.1 (s, 1C, CMe-cym) ppm. 31P NMR (chloroform-
d): -13.27 (s) ppm. FAB MS (m/z): 537 ([M - BF4]+); 403 ([M
- BF4 - C10H14]+). C10H14 ) p-cymene.
4
Ph); 7.28 (s, 1H, CH2-Im); 6.52 (t, 3JHH ≈ JHH ) 1.5, 1H, CH5-
4
Im); 6.28 (t, 3JHH ≈ JHH ) 1.5, 1H, CH4-Im); 5.28 (dd, 3JHH
)
6.1, JPH ) 1.2 1H, CH-cym); 5.24 (d, JHH ) 6.1, 1H, CH-cym);
3
5.14 (dd, JHH ) 6.1, JPH ) 1.3, 1H, CH-cym); 4.93 (d, JHH
)
6.1, 1H, CH-cym); 3.45 (d, 4JPH ) 11.1, 3H, MeO); 3.08 (s, 3H,
Me-Im); 2.52 (spt, JHH ) 6.9, 1H, CHMe2-cym); 1.89 (s, 3H,
CMe-cym); 1.11 (d, JHH ) 6.9, 3H, CHMe2); 1.10 (d, JHH ) 6.9,
3H, CHMe2) ppm. 13C NMR (chloroform-d): 164.35 (q, JCB
)
Preparation of [RuCl(C6H6)(K2-PN-dpim)]BF4 (2b). Tl-
BF4 (45 mg, 0.16 mmol) was added over a solution of 1b in
dichloromethane (20 mL). After 20 min of stirring the solution
become cloudy. The solution was stirred for 14 h. The white
precipitate was filtrated, and the resulting pale orange solution
was evaporated to dryness. The resulting solid was washed
with pentane (3 × 10 mL) and dried under vacuum. Yield:
0.073 g (0.13 mmol, 83%). Anal. Calcd for C22H21BClF4N2PRu
(567.51): C, 46.55; H, 3.73; N, 4.94. Found: C, 46.6; H, 3.51;
N, 5.31. IR (KBr, cm-1): 1058 νd(BF4), 547 δd(BF4-). 1H NMR
(chloroform-d): 7.85 (m, 2H, ortho-Ph); 7.6 (m; 4H, meta-Ph;
1H, CH-Im); 7.51 (m, 2H, ortho-Ph); 7.32 (m; 2H, para-Ph; 1H
CH-Im); 5.77 (d, JPH ) 1.01, 6H, C6H6); 3.63 (s, 3H, Me-Im)
ppm. 13C NMR (Chloroform-d): 138.0-127.0 (m, 15C, Ph, CH
and C2-Im); 87.1 (d, JPC ) 3.17, 6C, C6H6); 35.12 (s, 1C, Me-
Im) ppm. 31P NMR (chloroform-d): -6.03 (s) ppm. FAB MS
(m/z): 481 ([M - BF4]+); 446 ([M - BF4 - Cl]+); 403 ([M -
BF4 - C6H6]+).
49.3, 4C, ipso-Ph-BPh4); 140.74 (d, JCP ) 1.8, 1C, CH2-Im);
136.52 (q, JCB ) 1.5, 4C, ortho-Ph-BPh4); 132.83 (d, 4JPC ) 1.7,
3
1C, CH4-Im); 132.76 (d, JPC ) 48.1, 1C, ipso-Ph); 132.69 (d,
1
2JPC ) 10.9, 2C, ortho-Ph); 132.36 (d, JPC ) 2.2, 1C, para-
4
Ph); 131.86 (d, 2JPC ) 9.9, 2C, ortho-Ph); 131.46 (d, 4JPC ) 2.8,
1
1C, para-Ph); 129.72 (d, JPC ) 46.5, 1C, ipso-Ph); 128.87 (d,
3JPC ) 10.4, 2C, meta-Ph); 128.07 (d, JPC ) 10.1, 2C, meta-
3
Ph); 125.82 (q, JCB ) 2.7, 4C, meta-Ph-BPh4); 122.45 (s, 1C,
CH5-Im); 122.03 (s, 4C, para-Ph-BPh4); 116.64 (d, JPC ) 5.4,
1C, C4-cym); 102.43 (d, JPC ) 1.5, 1C, CMe-cym); 89.59 (d, JPC
) 1.4, 1C, CH2-cym); 89.5 (d, JPC ) 2.5, 1C, CH6-cym); 88.87
(d, JPC ) 6.1, 1C, CH3-cym); 87.74 (d, JPC ) 2.8, 1C, CH5-cym);
56.92 (d, 3JPC ) 13.4, 1C, P-OMe); 34.78 (s, 1C, Me-Im); 31.00
(s, 1C, CHMe2-cym); 22.23 (s, 1C, CHMe2-cym); 22.06 (s, 1C,
CHMe2-cym); 18.63 (s, 1C, CMe-cym) ppm. 31P NMR (chloro-
form-d): 128.84 (s) ppm. FAB mass (m/z): 569 ([M] - BPh4+);
487 ([M - BPh4 - MeImH]+); 452 ([M - BPh4 - MeImH -
HCl]+); 421 ([M - BPh4 - MeImH - Cl - MeO]+).
Preparation of [RuCl(C6H6)(K1-N-MeIm)(K1-P-P(O-Me)-
Ph2)]BF4 (3b). Over a solution of 1b (123 mg, 0.24 mmol) in
10 mL of dichloromethane another solution of NaBF4 (26.7 mg,
0.24 mmol) in 10 mL of methanol was added. The mixture was
stirred for 22 h. The solution was evaporated to dryness, and
the residue was extracted with dichloromethane (5 mL). The
resulting solution was filtered and evaporated to dryness. The
resulting oil was triturated with pentane (15 mL). 3b was
obtained as a yellow solid after filtration. Yield: 0.122 g (0.204
mmol, 85%). Anal. Calcd for C23H25BClF4N2OPRu (599.5): C,
46.04; H, 4.17; N, 4.67. Found: C, 46.25; H, 4.09; N, 4.74. IR
Preparation of [RuCl(p-cymene)(K1-N-MeIm)(K1-P-
P(OMe)Ph2)]X; X ) BF4 (3a), BPh4 (3d). Over a solution of
1a (130 mg, 0.23 mmol) in 10 mL of dichloromethane another
solution of NaBF4 (24.9 mg, 0.23 mmol) in 10 mL of methanol
was added. The mixture was stirred for 21 h. The solution was
evaporated to dryness, and the residue was extracted with
dichloromethane (5 mL). The resulting solution was filtered
and evaporated to dryness. The resulting oil was triturated
with pentane (15 mL). 3a was obtained as a yellow solid after
filtration. Yield: 0.149 g (0.168 mmol, 73%). An identical
procedure was followed for 3d using the corresponding amount
of NaBPh4 as precipitating salt.

Ruthenium Arene Derivatives
Organometallics, Vol. 23, No. 24, 2004 5705
(KBr, cm-1): 1055 νd(BF4-); 541 δd(BF4-); Nujol: 294 ν(Ru-
Cl). 1H NMR (chloroform-d): 7.78 (s, 1H, CH2-Im); 7.6-7.2 (m,
solid of 4c. Yield: 0.030 g (0.045 mmol, 90%). Anal. Calcd for
C27H29BCl2F4NPRu (657.29): C, 49.34; H, 4.45; N, 2.13.
Found: C, 49.09; H, 4.41; N, 2.18. IR (Nujol, cm-1): 1051
νd(BF4-); 524 δd(BF4-); 328 ν(RuCl). 1H NMR (acetone-d6): 9.15
(m, 1H, py); 8.68 (m, 1H, py); 8.27 (m, 1H, py); 8.11 (m, 1H,
py); 7.94 (m, 4H, ortho-Ph); 7.72 (m, 6H, meta- and para-Ph);
5.79 (d, JHH ) 6.4, 2H, CH-cym); 5.62 (d, 2H, CH-cym); 2.61
(spt, 3JHH ) 7.1, 1H, CHMe2-cym); 1.89 (s, 3H, CMe-cym); 1.12
4
10H, 2Ph); 7.15 (t, 3JHH ≈ JHH ) 1.5, 1H, CH5-Im); 6.6 (t, 3JHH
4
4
≈ JHH ) 1.5, 1H, CH4-Im); 5.9 (s, 6H, C6H6); 3.57 (d, JPH
)
12, 3H, MeO); 3.57 (s, 3H, Me-Im) ppm. 13C NMR (chloroform-
d): 143.1 (s, 1C, CH2-Im); 132.82 (d, JPC ) 51.2, 1C, ipso-
1
2
4
Ph); 132.77 (d, JPC ) 11.1, 2C, ortho-Ph); 132.27 (d, JPC
)
2.3, 1C, para-Ph); 131.85 (d, 2JPC ) 10.4, 2C, ortho-Ph); 131.51
(s, 1C, CH4-Im); 131.49 (d, JPC ) 2.2, 1C, para-Ph); 130.25
(d, JHH ) 6.9, 6H, CHMe2-cym) ppm. 13C NMR (acetone-d6):
4
3
(d, 1JPC ) 48.4, 1C, ipso-Ph); 128.78 (d, 3JPC ) 10.5, 2C, meta-
Ph); 128.34 (d, 3JPC ) 10.5, 2C, meta-Ph); 121.31 (s, 1C, CH5-
135.09 (d, JPC ) 10.5, 4C, ortho-Ph); 128.74 (d, JPC ) 2.5,
2
4
2C, para-Ph); 130.32 (d, 3JPC ) 10.0, 4C, meta-Ph); 147.29 (d,
3
1
Im); 91.09 (d, JPC ) 3.4, 6C, C6H6); 56.6 (d, JPC ) 11.4, 1C,
1JPC ) 3.4, py); 143.53 (d, JPC ) 5.0, py); 133.22 (py), 129.41
OMe); 34.92 (s, 1C, Me-Im). 31P NMR (chloroform-d): 130.27
(s) ppm. FAB mass (m/z): 513 ([M - BF4]+, 55%); 431 ([M -
BF4 - MeImH]+, 100%); 395 ([M - BF4 - MeImH - HCl]+,
80%), 365([M - BF4 - MeImH - MeO - Cl]+, 100%).
(py); 112.17 (d, JCP ) 3.1, 1C, CiPr-cym); 100.01 (s, 1C, CMe-
cym); 89.33 (d, JPC ) 5.0, 2C, CH2,6-cym or CH3,5-cym); 89.94
(d, JPC ) 5.0, 2C, CH2,6-cym or CH3,5-cym); 31.31 (s, 1C,
CHMe2-cym); 21.98 (s, 2C, CHMe2-cym); 17.85 (s, 1C, CMe-
cym) ppm. 31P NMR (acetone-d6): 21.98 (s) ppm.
Preparation of [RuCl2(p-cymene)(K1-P-dpimH)]BF4 (4a).
Over a solution of 1a (0.080 g, 0.14 mmol) in acetone (30 mL)
a solution of HBF4 (19.3 µL of a solution 54% w/w, 0.14 mmol)
in diethyl ether was added. The solution was stirred for 15
min, and the solution was evaporated to dryness. The resulting
oil was washed with pentane (15 mL), giving a red solid of 4a.
Yield: 0.085 g (0.13 mmol, 92%). Crystals of 4a‚CH2Cl2
suitable for an X-ray determination were obtained from CH2-
Cl2/hexane. Anal. Calcd for C27H32BCl4F4N2PRu (745.20): C,
43.52; H, 4.33; N, 3.76. Found: C, 43.65; H, 4.25; N, 3.85. IR
(KBr, cm-1): 1058 νd(BF4-); 535 δd(BF4-); Nujol: 348, 293
ν(Ru-Cl). 1H NMR (chloroform-d): 13.1 (bs, 1H, NH); 7.94 (m,
4 H, ortho-Ph); 7.64 (m, 6H, meta and para-Ph); 7.6 (s, 1H,
CH4-Im); 7.38 (s, 1H, CH5-Im); 5.46 (d, JHH ) 5.6, 2H, CH-
cym); 5.38 (d, JHH ) 5.6, 2H, CH-cym); 3.26 (s, 3H, Me-Im);
2.54 (spt, 3JHH ) 6.9, 1H, CHMe2-cym); 1.75 (s, 3H, CMe-cym);
0.85 (d, 3JHH ) 6.9, 6H, CHMe2-cym) ppm. 13C NMR (acetone-
d6): 138 (d, 1JPC ) 65.3, 1C, C2-Im); 134.3 (d, 1JPC ) 21.8, 2C,
Monitoring of the Transformation of 1a, 2a, or 4a in
Methanol-d4 with Time. The reaction of 1a, 2a, or 4a with
1
methanol-d4 at 25 °C to give 3a or 3e was monitored by H
NMR spectroscopy. The intensity of the Me-Im signals of each
complex was taken into account to express graphically the
evolution of the reactions and to calculate the different kinetic
constants.
A sample of 1a (4 mg, 0.007 mmol) was introduced into an
NMR tube (5 mm). Air was evacuated, and 350 µL of methanol-
d4 and 100 µL of chloroform-d were introduced into the tube
with a microsyringe (500 µL). The tube was sealed and a
homogeneous solution was formed after shaking. The reaction
was monitored by 1H NMR spectroscopy during 12 h by
introducing the tube into the probe, which had been previously
equilibrated to 25 °C. A similar procedure was used to follow
the reaction of 2a (4 mg, 0.006 mmol) with methanol-d4 (350
µL of methanol-d4 and 100 µL of chloroform-d) or from 4a (4
mg, 0.006 mmol) and 450 mL of methanol-d4.
ipso-Ph); 133.1 (d, 2JPC ) 10.7, 4C, ortho-Ph); 133.1 (d, 4JPC
)
2.4, 2C, para-Ph); 130 (d, 3JPC ) 10.7, 4C, meta-Ph); 128.6 (s,
1C, CH4-Im); 127.8 (s, 1C, CH5-Im); 111.1 (s, 1C, CiPr-cym);
97.2 (s, 1C, CMe-cym); 92.1 (d, JPC ) 4.3, 2C, CH2,6-cym); 87.4
(d, JPC ) 6.2, 2C, CH3,5-cym); 37.6 (s, 1C, Me-Im); 30.5 (s, 1C,
CHMe2-cym); 20.8 (s, 2C, CHMe2-cym); 16.9 (s, 1C, CMe-cym)
ppm. 31P NMR (chloroform-d): 23.92 (s) ppm. FAB MS (m/z):
573 ([M - BF4]+); 537 ([M - BF4 - H - Cl]+); 403 ([M - BF4
- H - Cl - (C10H14)]+). C10H14 ) p-cymene.
Analogous reactions for 1a and 2a were monitored in the
presence of LiCl. For instance, a sample of 2a (4 mg, 0.006
mmol) and LiCl (1.6 mg, 0.038 mmol) were dissolved in an
NMR tube with 1 mL of methanol-d4 and 1 µL of chloroform-
d. The reaction was monitored by 1H NMR spectroscopy as
outlined above.
Kinetic Measurements. The reaction of 1a or 2a with
methanol was studied using a Shimadzu UV-160 spectropho-
tometer. The progress of the reaction was followed by measur-
Preparation of [RuCl2(C6H6)(K1-P-dpimH)]BF4 (4b).
Over a suspension of 1b (0.050 g, 0.09 mmol) in acetone (30
mL) a solution of HBF4 (12.2 µL of a solution 54% w/w, 0.09
mmol) in diethyl ether was added. The solution was stirred
for 15 min, and the solution was evaporated to dryness. The
resulting oil was washed with pentane (15 mL), giving a red
solid of 4b. Yield: 0.052 g (0.086 mmol, 89%). Crystals of 4b
suitable for an X-ray determination were obtained from CH2-
Cl2/hexane. Anal. Calcd for C22H22BCl2F4N2PRu (604.17): C,
43.74; H, 3.67; N, 4.64. Found: C, 43.59; H, 3.73; N, 4.73. IR
(KBr, cm-1): 1061 νd(BF4-); 538 δd(BF4-); Nujol: 358, 319
ν(Ru-Cl). 1H NMR (acetone-d6): 13.04 (bs, 1H, NH); 8.08 (m,
4H, ortho-Ph); 7.89 (pst, 1H CH-Im); 7.73 (m, 7H, meta- and
para-Ph; 1H, CH-Im) 5.84 (d, JPH ) 0.9, 6H, C6H6); 3.53 (s,
3H, Me-Im) ppm. 13C NMR (acetone-d6): 133.76 (d, 2JPC ) 11.3,
ing the optical absorbance of 1a at 373 nm (ꢀ ) 2933 M-1 cm-1
)
or 2a at 199 nm (ꢀ ) 1322 M-1 cm-1). All the kinetic runs were
initiated by addition of methanol to a solution that contained
the complex 1a or 2a in chloroform. The initial rates method
was used for the kinetic analysis.
Hydrogen Transfer Catalysis with the Precatalysts 1a
and 2a. In a typical procedure without base, the substrate,
cyclohexanone (2 mL, 19.26 mmol), was added to a solution of
the precatalyst 1a (5.51 mg, 9.63 × 10-3 mmol) in 2-propanol
(15 mL) (ketone:precatalyst ) 2000:1) and the mixture was
stirred at the reflux temperature.
In a typical procedure with base, the substrate, cyclohex-
anone (2 mL, 19.26 mmol), was added to a solution of the
precatalyst 1a (5.51 mg, 9.63 × 10-3 mmol) and KOH (177
mg, 3.2 mmol) in 2-propanol (15 mL) (ketone:precatalyst:KOH
) 2000:1:333) and the mixture was stirred at the reflux
temperature.
Hydrogenation with Molecular Hydrogen. The hydro-
genation reactions were carried out in an autoclave with a
pressure of 30 atm of H2 in a thermostatic bath and with
magnetic stirring. In a typical procedure, the substrate,
phenylacetylene (1.1 mL, 10 mmol), was added to a solution
of the precatalyst 2a (6.2 mg, 1 × 10-2 mmol) in 2-propanol
(15 mL) (substrate:precatalyst ) 1000:1).
Conditions of the GC analysis: glass capillary column HP-
PPFA (30 m × 0.25 mm × 0.25 µm). He as carrier gas. In the
analysis of the hydrogenation of cyclohexanone, the column
4
4C, ortho-Ph); 133.33 (d, JPC ) 2.5, 2C, para-Ph); 130.1 (d,
3JPC ) 10.8, 4C, meta-Ph); 128.53 (s, 1C, CH-Im); 128.46 (s,
1
1
1C, CH-Im); 127.86 (d, JPC ) 50, 2C, ipso-Ph); 121.4 (d, JPC
) 2.8, 1C, C2-Im); 90.55 (d, JPC ) 3.6, 6C, C6H6); 37.94 (s, 1C,
Me-Im) ppm. 31P NMR (acetone-d6): 35.1 (s) ppm. FAB MS
(m/z): 517 ([M - BF4]+); 481 ([M - BF4 - H - Cl]+); 403 ([M
- BF4 - H - Cl - (C6H6)]+).
Preparation of [RuCl2(p-cymene)(K1-P-PPh2pyH)]BF4
(4c). Over a suspension of 1c (0.030 g, 0.05 mmol) in acetone
(10 mL) a solution of HBF4 (8 µL of a solution 54% w/w, 0.09
mmol) in diethyl ether was added. The solution was stirred
for 20 min and evaporated to dryness. The resulting oil was
triturated with diethyl ether (2 × 10 mL), giving an orange

5706 Organometallics, Vol. 23, No. 24, 2004
Caballero et al.
was heated at 80 °C during 0.8 min and afterward heated at
12 °C/min to 110 °C. tR(cyclohexanone) ) 2.142 min, tR-
(cyclohexanol) ) 2.947 min. In the analysis of the hydrogena-
tion of phenylacetylene, the column was heated at 60 °C during
1 min and afterward heated at 10 °C/min to 80 °C. tR-
(phenylacetylene) ) 4.64 min, tR(styrene) ) 3.069 min, tR-
(ethylbenzene) ) 1.776 min, 60 °C (1min) to 80 °C (3.5min) at
10 °C/min.
for financial support. We also thank J. J. Delgado from
SCAI, University of Burgos, Spain, for carrying out
elemental analyses.
Supporting Information Available: Tables and CIF files
of X-ray structural data, including data collection parameters,
positional and thermal parameters, bond distances and angles
for complexes, and additional structural views of complexes
1a, 1b, 4a, and 4b. This material is available free of charge
via the Internet at http://pubs.acs.org.
Acknowledgment. We are grateful to the Spanish
DGES/MCyT (Project No. BQU-2002-00286) and Con-
sejer´ıa de Ciencia y Tecnolog´ıa of JCCLM (PBI-02-002)
OM049438O