(Arene)ruthenium(II) complexes containing substituted bis(pyrazolyl)methane ligands - Catalytic behaviour in transfer hydrogenation of ketones

Article abstract of DOI:10.1002/ejic.200700267

A new and safer methodology has been developed for the synthesis of bis(pyrazol-1-yl)methane ligands (NN). Several ligands containing different phenyl groups on the central carbon atom have been obtained. Ruthenium derivatives of the type [Ru(arene)Cl(NN)]BPh₄ (arene = benzene, p-cymene) have been synthesised using these ligands. One or two isomers that differ regarding the axial or equatorial disposition of the phenyl group on the metallacycle have been obtained. Their formation is rationalised by considering steric effects. The structures of five derivatives were determined by X-ray diffraction. In four complexes the phenyl substituent is in the axial disposition of the metallacycle and in one case in the equatorial orientation. The dihedral angle formed by the planes of the two pyrazole rings is always bigger for the complexes containing unsubstituted pyrazolyl heterocycles. The behaviour of the new derivatives in the transfer hydrogenation of benzophenone in the presence of KOH was studied. The benzene derivatives showed higher activity than the p-cymene complexes. A marked and positive effect of the methyl groups on the pyrazolyl rings was observed. The effect of the substituents on the benzyl carbon atom was also important. It has been observed that the benzophenone hydrogenation was possible without the addition of complexes. The effect of the KOH concentration was evaluated and a concentration that leads to negligible conversion in a base-only process was chosen. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700267

FULL PAPER
DOI: 10.1002/ejic.200700267
(Arene)ruthenium(II) Complexes Containing Substituted Bis(pyrazolyl)methane
Ligands – Catalytic Behaviour in Transfer Hydrogenation of Ketones
M. Carmen Carrión,[a] Félix A. Jalón,[a] Blanca R. Manzano,*[a] Ana M. Rodríguez,[b]
Francisco Sepúlveda,[a] and Miguel Maestro[c]
Dedicated to the memory of Prof. S. Trofimenko
Keywords: Ruthenium / Arene ligands / Homogeneous catalysis / Bis(pyrazolyl)methane / Transfer hydrogenation / X-ray
structure determination
A new and safer methodology has been developed for the
synthesis of bis(pyrazol-1-yl)methane ligands (NN). Several
ligands containing different phenyl groups on the central
carbon atom have been obtained. Ruthenium derivatives of
the type [Ru(arene)Cl(NN)]BPh4 (arene = benzene, p-cy-
mene) have been synthesised using these ligands. One or
two isomers that differ regarding the axial or equatorial dis-
position of the phenyl group on the metallacycle have been
obtained. Their formation is rationalised by considering ste-
ric effects. The structures of five derivatives were determined
by X-ray diffraction. In four complexes the phenyl substitu-
ent is in the axial disposition of the metallacycle and in one
case in the equatorial orientation. The dihedral angle formed
by the planes of the two pyrazole rings is always bigger for
the complexes containing unsubstituted pyrazolyl hetero-
cycles. The behaviour of the new derivatives in the transfer
hydrogenation of benzophenone in the presence of KOH was
studied. The benzene derivatives showed higher activity
than the p-cymene complexes. A marked and positive effect
of the methyl groups on the pyrazolyl rings was observed.
The effect of the substituents on the benzyl carbon atom was
also important. It has been observed that the benzophenone
hydrogenation was possible without the addition of com-
plexes. The effect of the KOH concentration was evaluated
and a concentration that leads to negligible conversion in a
base-only process was chosen.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
been described for this process including PP, NN, NO and
NPN ligands.[5] In this context, one of the most important
breakthroughs was discovered by Noyori and involves the
use of “RuII(arene)” precursors with chiral amino alcohols
or diamines[6] in processes that lead to excellent activities
and enantioselectivities. Because of the participation of the
ligand in the catalytic reaction, Noyori has proposed the
term bifunctional metal-ligand catalysis for this kind of
process. He performed theoretical calculations concerning
the mechanism and the origin of enantioselectivity.[7] Other
groups have also developed systems based on Ru–arene
fragments with amino alcohols,[8] amino amide[9] or amino
carboxylate[10] ligands. Interesting papers concerning
(Arene)ruthenium(II) complexes constitute an important
group of derivatives that have applications in numerous
catalytic processes. Although some ruthenium derivatives
containing poly(pyrazolyl)borate[1] or poly(pyrazolyl)meth-
ane[2] ligands have been reported, arene complexes with
these groups[3] are extremely scarce. One of the catalytic ap-
plications of arene–ruthenium derivatives is in the transfer
hydrogenation of ketones. This process gives high yields and
enantiomeric excesses with some ketones and has the ad-
vantage over the traditional use of H2 pressure of greater
operational simplicity.[4] Different Ru–arene systems have
[a] Departamento de Química Inorgánica, Orgánica y Bioquímica, mechanisms have also appeared.[11] Besides the metal ligand
Universidad de Castilla-La Mancha, Facultad de Químicas,
bifunctional mechanism, other mechanisms involving
Avda. C.J. Cela 10, 13071 Ciudad Real, Spain
monohydride or dihydride species have been proposed. Al-
though not involving arene derivatives, it is worth noting
that recently Baratta et al.[12] designed a new type of RuII
catalyst, containing the ligand 2-(aminomethyl)pyridine or
its derivatives, that was active in the transfer hydrogenation
of acetophenone, using NaOH as cocatalyst with TOF up
to 4.0ϫ105 h–1.
[b] Departamento de Química Inorgánica, Orgánica y Bioquímica,
Universidad de Castilla-La Mancha, Escuela Técnica Superior
de Ingenieros Industriales,
Avda. C.J. Cela 3, 13071 Ciudad Real, Spain
[c] Departamento de Química Fundamental, Universidade da
Coruña,
15071 A Coruña, Spain
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2007, 3961–3973
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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B. R. Manzano et al.
FULL PAPER
In recent years we have worked with a series of bis(pyr- drogenation transfer of ketones, another goal was the use
azolyl)methane derivatives.[2a,13] These compounds offer the of the new complexes as precatalysts in these processes
possibility of modulating the steric and electronic properties using 2-propanol as the solvent and reducing agent. Prelim-
by introducing substituents in the pyrazole rings and at the inary tests will be presented. The NN ligands are clearly
central carbon atom. We used ligands that contained dif- different to those used by Noyori because of the absence of
ferently substituted phenyl rings and pyrazole (pz) or 3,5- NH groups as donor centres. In any case, it was of interest
dimethylpyrazole (pz*) heterocycles attached to the central to evaluate the effect of the functional groups on the benzyl
carbon atom. We have also explored the coordination carbon atom outside the coordination centre including the
chemistry of these ligands, mainly with palladium frag- NH2 fragment.
ments.[13] An endobidentate coordination with the forma-
tion of metallacycles with a boat conformation has always
been found. Interestingly, in all cases the phenyl substituent
occupies the axial position in this metallacycle (see
Scheme 1a). This is probably due to the steric hindrance
Results and Discussion
that these groups would cause if they were in an equatorial
position with respect to the pyrazole rings (Scheme 1b) and
also the absence of other interactions in the axial position
because of the square-planar environment of the metal cen-
tre. We found that with substituted pyrazolyl rings, the bite
angle and the dihedral angle formed by the planes NPdN/
N4 were smaller and this influenced the dynamic behaviour
of some derivatives.[13c] These data were rationalised by
means of theoretical calculations.[14] Bis(pyrazolyl)methane
complexes in which the substituent (pyrazole or thienyl) on
the central CH group is situated in an equatorial position
correspond to octahedral derivatives of ruthenium(II)[15] or
platinum(IV).[16] In both cases, the pyrazolyl rings were un-
substituted.
Synthesis of the Ligands and Complexes
The ligands used in this work and their abbreviations are
summarised in Scheme 2.
Scheme 2.
[13c]
The ligands bpz*mPh,[17] bpzmPhOCH3
and
bpz*m[18] have been described previously. The ligands
bpz*mArNO2, bpzmArNO2 and bpz*mArNH2 are de-
scribed in this work for the first time. Until now, the inter-
mediate bis(pyrazol-1-yl)ketone that is necessary for the
preparation of these types of ligand, was synthesised by the
reaction of pyrazole (substituted or not) and phosgene. In
this work we tried to develop a greener method that could
avoid the use of this highly toxic gas. The alternative that
we have found is the use of the solid triphosgene. Thus, the
synthesis of the ligands bpzmPh, bpz*mArNO2 and
bpzmArNO2 was carried out in the following way. Firstly,
the bis(pyrazol-1-yl)ketone species were obtained through
the reaction of the corresponding pyrazole with triphosgene
in the presence of triethylamine (Scheme 3).
Scheme 1.
In the work described here we decided to synthesise a
series of bis(pyrazolyl)methane ligands in which the central
carbon atom bears phenyl rings that have different func-
tional substituents such as OCH3, NO2 or NH2. One objec-
tive was to find a method of synthesis that avoided the use
of toxic phosgene. The purpose was also the synthesis of
new arene (benzene, p-cymene) ruthenium derivatives that
contain these ligands. Ultimately, we were interested in
evaluating the stereochemistry of these complexes and, in
particular, the preference for an equatorial or axial disposi-
tion of the phenyl ring and the relationship of this fact with
the substitution on the pyrazolyl groups and the steric
requirements of the arene. An open question concerned
whether the change in the type of pyrazole present would
also force the same type of distortions found in the related
palladium chemistry.
Scheme 3.
The resulting ketone subsequently reacted with the corre-
Taking into account that Ru–arene complexes with poly- sponding aldehyde in toluene under reflux for 24 h
(pyrazolyl)methane ligands have never been studied in hy- (Scheme 4).
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(Arene)ruthenium(II) Complexes with Bis(pyrazolyl)methane Ligands
FULL PAPER
spectroscopic data are gathered in Table S1 of the Support-
ing Information. Coordination of the nitrogenated ligand
to the [RuCl(arene)]+ fragment results in shifts that, in some
cases, were greater than 1 ppm towards higher frequencies
for the pyrazolyl ring proton resonances. The same trend
was observed for the 13C NMR resonances in cases where
the appropriate data for direct comparison are available.
This effect was attributed in general to the electron do-
nation of the ligand to the metal cation (the effect of other
groups in the molecule on specific protons will be detailed
below). The increased electron deficiency of the heterocyclic
Scheme 4.
1
rings also leads to an increase in the H,1H coupling con-
The ligand bpz*mArNH2 was obtained by hydrogena-
tion of bpz*mArNO2 using a Pd/C catalyst.
stants.[19] The assignment of structures to the complexes
was done mainly by means of the NOESY spectra. The two
possible structures are shown in Scheme 5. These com-
pounds differ in the axial or equatorial orientation of the
phenyl ring in the metallacycle. The arrows represent the
most important NOEs observed. The disposition of the ar-
ene ring bonded to Ru and the chloride proposed in the
scheme is thought to be the only possible situation for steric
reasons. In the complexes obtained with methylated ligands
and the isomers labelled A for the nonmethylated ones, an
NOE is always observed between Hα and H5 (or Me5) of the
pyrazolyl groups. In some cases, an NOE is also observed
between resonances of the arene groups and the H atom of
the phenyl group ortho to the benzyl carbon atom. These
data indicate that in these complexes the phenyl ring is situ-
ated in an axial position. The structures in which the phenyl
ring is in an equatorial disposition are assigned to isomers
B. In fact, in complex 12B an NOE was observed between
Hα and the proton H3 of the p-cymene ring. Although it
does not provide structural information, a noticeable NOE
The RuII–arene (arene = benzene, p-cymene) complexes
used in this work were obtained by treating the correspond-
ing RuII starting material, the nature of which depends on
the arene, with the desired ligand in MeOH with the ad-
dition of Na[BPh4] at the end of the reaction [see Equa-
tions (1) and (2)].
(1)
NN = bpz*m, 1; bpz*mPh, 3; bpzmPh, 5; bpzmArOCH3, 7;
bpz*mArNO2, 9; bpzmArNO2, 11; bpz*mArNH2, 13.
(2)
NN = bpz*m, 2; bpz*mPh, 4; bpzmPh, 6; bpzmArOCH3, 8; is frequently observed in both types of isomer between the
H3 or Me3 pyrazole resonances and signals from the arenes.
bpz*mArNO2, 10; bpzmArNO2, 12; bpz*mArNH2, 14.
This must be a consequence of the large dihedral angle
In cases where the nitrogenated ligands contained meth-
NRuN/N4 in the metallacycle having the boat conformation
ylated pyrazolyl groups, only one isomer was obtained for
(see X-ray structures described below).
the corresponding ruthenium complexes. A different situa-
tion was found when the ligand contained unsubstituted
pyrazoles. Apart from the complexes containing bpzmPh,
where only one isomer was found, the other derivatives exist
as a mixture of two isomers (A and B). The relative ratios
of these isomers, determined by NMR before recrystalli-
sation, are shown, where applicable, in the Experimental
Section.
The new complexes were characterised by elemental
1
analysis as well as IR, H and 13C NMR spectroscopy and,
in some cases, by X-ray diffraction. The bands correspond-
ing to the stretching vibrations of the NO2 and NH2 groups
were observed in the IR spectra (see Exp. Sect.).
Scheme 5. Isomers A and B for the arene–RuII derivatives. The
most important NOEs are indicated with arrows. The steric interac-
tions used to rationalise the isomer ratio are indicated by the roman
numerals I and II. RЈЈ means that the arene ring is benzene or p-
NMR Study
cymene.
A careful NMR analysis of the new ligands and com-
plexes was carried out. The assignment of the resonances
Concerning the 1H NMR chemical shifts of the reso-
was possible with the help of 1H,1H-COSY, NOESY and g- nances of the two isomers, it is expected that the resonances
HMQC spectra (in some cases also with g-HMBC) and by of the H5 pyrazole protons or even those of the arene rings
considering the values of coupling constants. The 1H NMR would be affected by the position of the phenyl groups. In
Eur. J. Inorg. Chem. 2007, 3961–3973
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B. R. Manzano et al.
FULL PAPER
fact, the H5 (pz) protons for isomers A appear in the range 90 min, which constitutes a clear indication that intercon-
8.23–8.50 ppm and those of isomers B in the range 7.69– version between isomers is possible. There is no signal co-
7.80 ppm. When the phenyl groups are in an equatorial po- alescence or broadening of the resonances. Consequently,
sition, it is clear that these H5 protons are more shielded. the energy of the process is high enough not to be observ-
This must be due to the effect of the current anisotropy of able by coalescence methods. This process cannot take place
the aromatic rings. A similar effect is observed for the aro- through a boat-to-boat interconversion of the metallacycle,
matic resonances of the arenes. For example, the benzene because, although the axial or equatorial position of the
signals of isomers A are in the region 4.90–5.75 ppm phenyl rings will change with this process, it would not lead
whereas isomers B give rise to signals in the range 6.24– to the other isomer but to a species that we consider un-
6.27 ppm. This observation implies that, although the stable for steric reasons (see Scheme 6). A possible way of
phenyl rings will rotate around the C(ipso)–Cα bond, the isomer interconversion is through a partial decoordination
preferred orientation for the A isomers is that in which the of the nitrogenated ligand.
ring forms an angle of approximately 90° with the Hα–Cα–
C(ipso) plane. This orientation also leads to an upfield shift
of the phenyl resonances of the protons situated ortho to
Cα, a situation due to the anisotropy effect of the pyrazole
rings. These resonances could serve as a way of identifying
the structure of a specific isomer. In the case of the 13C{1H}
NMR resonances, a clear difference is also observed in the
C5 pyrazole signals, similar to that observed in the 1H
NMR spectra. For example, a higher chemical shift (differ-
ence of about 3–4 ppm) is observed for isomer A than iso-
mer B.
The formation of a single isomer or a mixture of isomers,
and even the ratio of isomers, can be rationalised on the
basis of steric effects alone. Steric hindrance between the
arene rings and the pyrazolyl groups exists in both isomers
and probably will not influence their ratio (see Scheme 5).
Steric hindrance I will be important in isomers B while ste-
ric hindrance II will be operating in isomers A. When the
pyrazolyl groups are methylated, interaction I must pre-
dominate to induce the unique formation of complexes of
type A. For the case of nonmethylated pyrazolyl groups,
interaction I will be less important and both interactions
may be competitive. In fact, both isomers are formed (see
isomer ratio of complexes 7, 8, 11 and 12; complexes 5 and
Figure 1. 1H NMR monitoring of the evolution of a 8A/8B mixture
6 with bpzmPh constitute an exception, see Exp. Sect.), al- with time.
beit in a ratio that depends on the nature of the arene. For
the benzene complexes, isomers of type A are dominant,
while for the bulkier p-cymene the ratio is nearly 1. In con-
clusion, in benzene derivatives interaction I is dominant
while for the p-cymene complexes both interactions must be
comparable. In the case of complexes with the ligand
bpzmPh where the phenyl group does not have a functional
group, it seems that interaction of type II is not very signifi-
Scheme 6.
cant and only isomers of type A are formed.
It is interesting to compare these data with those found
in square-planar palladium complexes,[13] in which the
phenyl ring is always situated in an axial position, even for
X-ray Structure Determinations
The molecular structures of complexes 7A·0.5C2H4Cl2,
methylallyl derivatives.[13a,13b] The reason must be that in
these types of derivatives the geometry of the metal centre
means that interactions of type II do not exist or are not 8B, 9, 10·0.5C2H4Cl2 and 12A were determined by X-ray
important. diffraction analysis. The crystallographic data are gathered
In the case of complex 8 we obtained a crystallised sam- in Table 1 and the most important bond lengths and angles,
ple that was enriched in isomer B and we monitored the including some dihedral angles, are given in Table 2. The
evolution of this sample at 50 °C in a [D6]acetone solution. corresponding ORTEP drawings are shown in Figures 2, 3,
Figure 1 reflects the changes that were observed with time. 4, 5 and 6. In the case of 10, two independent molecules
The initial ratio 8B/8A of 77:23 changed to 55:45 after exist in the asymmetric unit. The data for both are very
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(Arene)ruthenium(II) Complexes with Bis(pyrazolyl)methane Ligands
FULL PAPER
similar and only those of one molecule are given, in Table 2. Ru–N distances are shorter for the nonmethylated pyrazolyl
All complexes have a half-sandwich structure consisting of rings. The bite angle is in the range 83.4–85.5°. The values
the coordinated arene, a chloride and the bidentate nitro- of the dihedral angles NRuN/N4, which are listed in
genated ligand. In complexes 7, 9, 10 and 12 the phenyl Table 2, are in the range 151–169°. In contrast to the palla-
group has an axial disposition on the metallacycle having dium derivatives, there is no relationship in these ruthenium
the boat conformation. However, in the case of 8 we were complexes between the bite angle or the stated dihedral an-
fortunate to crystallise isomer B, in which this group is in gle and the nature of the substituent on the pyrazolyl rings.
an equatorial disposition. The distances between the Ru However, it is clear that the dihedral angle formed by the
centre and the coordinated atoms are in the expected range. planes of the two pyrazole rings is always bigger for the
The average Ru–C distances are slightly longer for the p- complexes containing unsubstituted pyrazolyl heterocycles.
cymene derivatives than for those containing benzene. The We propose that this effect is due to steric hindrance be-
Table 1. Crystallographic data for complexes 7A·0.5C2H4Cl2, 8B, 9, 10·0.5C2H4Cl2 and 12A.
7A·0.5C2H4Cl2
8B
9
10·0.5C2H4Cl2
12A
Empirical formula
Formula mass
Temperature [K]
Wavelength [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C45H42BCl2N4ORu
837.61
130(2)
0.71073
monoclinic
P21/n
9.8348(2)
35.361(1)
11.8454(3)
C48H48BClN4ORu
844.23
130(2) K
0.71073
monoclinic
P21/n
9.5852(4)
34.987(2)
12.3711(6)
C47H45BClN5O2Ru C52H55BCl2N5O2Ru C47H45BClN5O2Ru
859.21
298(2)
964.79
293(2)
859.21
298(2)
0.71073
monoclinic
P21/c
0.71073
triclinic
P1
0.71073
monoclinic
P21/c
¯
16.6942(6)
12.3963(5)
20.9589(8)
10.0732(5)
15.1007(8)
32.086(2)
18.022(1)
9.6950(8)
23.868(2)
90
79.224(1)
β [°]
106.500(1)
95.854(4)
107.375(1)
82.557(1)
82.630(1)
4727.1(4)
4
1.356
2004
99.785(2)
90
4109.8(6)
4
1.389
1776
γ [°]
V [Å3]
3949.8(2)
4
1.409
4127.1(3)
4
1.359
1752
4139.5(3)
4
1.379
1776
Z
Dcalcd [Mg·m–3
F(000)
]
1724
Crystal size [mm]
Limiting indices
0.26ϫ0.22ϫ0.18
–9 Յ h Յ 12
–44 Յ k Յ 44
–14 Յ l Յ 14
8053/0/488
0.57ϫ0.20ϫ0.13
–13 Յ h Յ 13
–49 Յ k Յ 49
–17 Յ l Յ 14
12548/0/509
2.83–30.53
1.043
0.50ϫ0.21ϫ0.16
–20 Յ h Յ 16
–13 Յ k Յ 15
–25 Յ l Յ 26
8458/0/514
1.93–26.37
1.014
0.18ϫ0.17ϫ0.12
–13 Յ h Յ 13
–18 Յ k Յ 20
–25 Յ l Յ 42
21595/0/1115
1.30–28.31
0.997
0.32ϫ0.24ϫ0.13
–19 Յ h Յ 24
–12 Յ k Յ 11
–31 Յ l Յ 30
9754/0/514
1.73–28.35
1.014
Data/restraints/parameters
θ range for data collection (°) 2.13–26.39
Goodness-of-fit on F2
1.058
Final R indices [I Ͼ 2σ(I)]
R1 = 0.0444
wR2 = 0.0971
1.064, –0.622
R1 = 0.0465
wR2 = 0.1019
1.494, –0.909
R1 = 0.0345
wR2 = 0.0789
0.363, –0.403
R1 = 0.0750
wR2 = 0.1577
1.439, –1.255
R1 = 0.0461
wR2 = 0.0920
0.665, –0.636
Largest diff. peak/hole [e·Å–3
]
Table 2. Selected bond lengths [Å], bond angles [°] and dihedral angles [°] for complexes 7A·0.5C2H4Cl2, 8B, 9, 10·0.5C2H4Cl2 and 12A.
7A·0.5C2H4Cl2 8B 10·0.5C2H4Cl2 12A
Ru1–N3
9
Ru1–N3
Ru1–N2
Ru1–Cl2
2.090(3)
2.101(3)
2.3940(8)
2.183
Ru1–N1
Ru1–N3
Ru1–Cl2
2.089(2)
2.069(2)
2.4019(6)
2.197
Ru1–N1
Ru1–N3
Ru1–Cl1
Ru1–Caverage
N1–Ru1–N3
2.116(2)
2.128(2)
2.3896(8)
2.185
Ru1–N1
Ru1–N3
Ru1–Cl1
Ru1–Caverage
N1–Ru1–N3
2.140(5)
2.141(5)
2.381(2)
2.211
83.6(2)
84.66
2.101(3)
2.105(3)
2.4134(9)
2.198
Ru1–N1
Ru1–Cl1
Ru1–Caverage
N3–Ru1–N1
Ru1–Caverage
N3–Ru1–N2 85.54(10) N3–Ru1–N1
Ru1–Caverage
83.41(8)
85.40(8)
83.8(1)
N3–Ru1–Cl2
N2–Ru1–Cl2
ε[a]
82.67(7) N3–Ru1–Cl2 84.78(6) N1–Ru1–Cl1 84.49(6) N1–Ru1–Cl1 84.7(1) N1–Ru1–Cl1 84.05(7)
84.90(7) N1–Ru1–Cl2 84.49(6) N3–Ru1–Cl1 85.23(6) N3–Ru1–Cl1 84.6(1) N3–Ru1–Cl1 85.56(7)
143.9
ε[a]
131.7
ε[a]
119.4
ε[a]
110.9
117.5
152.0
134.0
87.6
ε[a]
126.4
[b]
[b]
[b]
[b]
[b]
NRuN/N4
NCN/N4
168.8
133.5
56.1
NRuN/N4
151.2
131.7
10.8
NRuN/N4
160.3
129.1
85.9
NRuN/N4
NRuN/N4
161.8
133.1
78.3
[c]
[c]
[c]
[c]
[c]
NCN/N4
NCN/N4
NCN/N4
NCN/N4
ζ[d]
ζ[d]
ζ[d]
ζ[d]
ζ[d]
η[e]
65.9
η[e]
68.8
η[e]
54.4
[a] Dihedral angle between both pyrazole rings. [b] Dihedral angle between the plane formed by the four nitrogen atoms and the angle
formed by Ru and the two coordinated nitrogen atoms. [c] Dihedral angle between the plane formed by the four nitrogen atoms and the
angle formed by the benzyl carbon atom and the two noncoordinated nitrogen atoms. [d] Dihedral angle formed by the plane of the
phenyl ring and the plane formed by the atoms H–C–C(ipso) (phenyl ring). [e] Dihedral angle formed by the phenyl ring and the plane
of the NO2 group.
Eur. J. Inorg. Chem. 2007, 3961–3973
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B. R. Manzano et al.
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tween the methyl groups of the pyrazoles and the arene
groups. When the angle between the pyrazoles decreases,
this interaction may be reduced. This is clearly reflected in
the structure drawing and the space-filling representations
in Figure 7.
Figure 4. ORTEP view of the cation of complex 9. Displacement
ellipsoids are drawn at the 30% probability level. Hydrogen atoms
have been omitted for clarity.
Figure 2. ORTEP view of the cation of complex 7A·0.5C2H4Cl2.
Displacement ellipsoids are drawn at the 30% probability level. Hy-
drogen atoms have been omitted for clarity.
Figure 5. ORTEP view of the cation of complex 10·0.5C2H4Cl2.
Displacement ellipsoids are drawn at the 30% probability level. Hy-
drogen atoms have been omitted for clarity.
Figure 3. ORTEP view of the cation of complex 8B. Displacement
ellipsoids are drawn at the 30% probability level. Hydrogen atoms
have been omitted for clarity.
The orientation of the phenyl ring with respect to the
plane formed by the atoms Hα–Cα–C(ipso) is mainly de-
pendent on the axial or equatorial disposition of this ring.
When it is axial, the dihedral angle is very close to 90° (in
the case of 7A it is smaller: 56.12°), while for 8B (where the
group is equatorial) the value is only 10.79°.
The methoxy group is approximately in the plane of the
phenyl ring. However, it is worth noting the orientation of
the NO2 plane with respect to the corresponding phenyl
ring. Unexpectedly, these planes are not parallel, and the
values for the dihedral angle are in the range 65–68° for
Figure 6. ORTEP view of the cation of complex 12A. Displacement
ellipsoids are drawn at the 30% probability level. Hydrogen atoms
the methylated complexes and 54.4° for the nonmethylated have been omitted for clarity.
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(Arene)ruthenium(II) Complexes with Bis(pyrazolyl)methane Ligands
FULL PAPER
Figure 7. (a) Drawing scheme showing the steric interaction between the pyrazole Me3 groups and the CH bonds of the coordinated
benzene that influences the pz–pz interplanar angle (the same is applicable to the p-cymene derivatives). (b and c) Comparison of such
interactions in a space-fill drawing of the X-ray structures of complexes 7 and 9 respectively (Cl ligands and benzyl groups on the Cα
atom have been omitted for clarity).
system. A closer inspection of the structure provides a tion reactions of benzophenone using 2-propanol as the re-
plausible explanation for this observation. If the NO2 plane ducing agent and solvent in the presence of KOH as the
was parallel to the phenyl ring, one of the oxygen atoms base [Equation (3)]:
(with a negative charge density) would be situated very
PhCOPh + iPrOH Ǟ PhCHOHPh + Me2CO
(3)
close to the π electron density of one pyrazole ring, and
the aim of the torsion is probably to prevent this repulsive
interaction. On the other hand, another orientation of the
phenyl ring to minimise this problem would involve greater
steric hindrance, because the phenyl ring would be too close
to the arene that is bonded to the ruthenium centre (see
Scheme 7).
Conversion was not observed at room temperature. For
example, on using complex 7 there was no conversion after
36 h (see Exp. Sect. for conditions). Consequently, the boil-
ing point of the solvent (85 °C) was used as the temperature
in all the experiments. Initially we performed catalytic tests
with complexes 1 and 3 with a substrate/KOH/complex ra-
tio of 1000:100:1. Only moderate yields of the alcohol were
obtained after 24 h of reaction (28% for 1 and 15% for 3).
We decided to evaluate the influence of the base concentra-
tion and we increased the number of equivalents of KOH
without changing other factors. We performed tests with
250, 500 and 1000 of KOH per mole of complex and a
steady increase in the TOF number and yield was observed.
At this point it is necessary to consider the possibility of a
high effect of the base that could obscure the catalytic effect
of the complex. Processes of hydrogenation have been de-
scribed with molecular hydrogen of benzophenone with a
base (mainly tert-butoxide) in the absence of a catalyst, but
using very drastic conditions (about 200 °C, Ͼ100 bar
H2).[21] Regarding transfer hydrogenation, a conversion of
60% of acetophenone to the corresponding alcohol in boil-
ing 2-propanol with NaOH 0.5 [22] in 4 h and very low
activity in 0.02  KOH solutions has been reported.[23] Our
highest concentration was 0.2 . In any case, we decided to
perform an analysis of the base-only reaction at different
KOH concentrations. We found that KOH is able to cata-
lyse the benzophenone hydrogenation with 2-propanol at
85 °C. When the alcohol yield is represented against dif-
ferent KOH concentrations, a straight line with positive
slope (% yield = 0.91894 + 306.60015[KOH]; R = 0.99421)
is obtained. The results are reflected in Table 3. In Figure 8
a representation of conversion against time is reflected for
two experiments without a catalyst (KOH 0.008  and
0.2 ) and another two experiments with KOH 0.2  in the
presence of complexes 3 or 13 (substrate/KOH/complex ra-
Scheme 7.
As far as the orientation of the p-cymene ring in com-
plexes 8B, 10 and 12A is concerned, there are two situations
that are clearly different. In the case of complexes 10 and
12A, where the phenyl ring has an axial orientation, the
disposition of the p-cymene is such that the steric hindrance
with this ring is reduced. The orientation in the case of 8B,
where the anisole ring is in an equatorial position, is clearly
different and the isopropyl group is oriented towards the
methoxy group. Closer inspection of the structure of 8B
reveals the existence of a hydrogen bond between the C–H
fragment of the isopropyl group and the oxygen atom of
the methoxy group. The C···O distance is 3.427 Å and the
angle C–H–O is 142°. These data allow us to conclude that
this hydrogen bond is weak.[20]
Hydrogen Transfer Catalytic Tests
Preliminary tests were done concerning the behaviour of tio of 1000:1000:1). It is clear that when working with KOH
some of the new derivatives in catalytic transfer hydrogena- concentrations of 0.2  the effect of our complexes is very
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B. R. Manzano et al.
FULL PAPER
small and other conditions must be chosen. We think that pyrazoles and runs 6/13 and 7/14 for nonmethylated pyr-
these studies must be taken into account before performing azoles) is observed. However, a large increase in the activity
reactions of transfer hydrogenation in the presence of KOH. is observed when the OCH3 group is introduced on the
phenyl ring (runs 6/8 and 7/10). In all the experiments sam-
Table 3. Transfer hydrogenation of benzophenone with KOH with-
ples were taken at 1.5, 3, 6, 9 and 24 h (see Supporting
out Ru complexes.[a]
Information for the corresponding data).
[b]
[KOH] [mol·L–1]
Mol KOH [500 mol substrate] Yield [%]
Table 4. Transfer hydrogenation of benzophenone with Ru precata-
lysts.[a]
0.004
0.006
0.008
0.016
0.04
0.1
10
15
20
0
2
3
[b]
Run
Complex
NN ligand
TOF20 [h–1]
Yield[c] [%]
40
7
1[d]
2
3
4
5
6
7
8
–
1
–
–
35
25
62
31
8
5
100
250
500
750
10
36
68
88
bpz*m
bpz*m
bpz*mPh
bpz*mPh
bpzmPh
bpzmPh
bpzmArOCH3
bpzmArOCH3
bpzmArOCH3
bpz*mArNO2
bpz*mArNO2
bpzmArNO2
bpzmArNO2
bpz*mArNH2
bpz*mArNH2
62
61
97
82
37
10
90
82
90
60
60
18
8
2
0.2
0.3
3
4
[a] Conditions: 2 mmol of benzophenone, 10 mL of iPrOH, reflux
(82 °C). [b] Yield of diphenylmethanol after 13 h.
5
6
–
7
125
125
50
18
15
–
–
45
29
9[e]
10
11
12
13
14
15
16
7
8
9
10
11
12
13
14
74
66
[a] Conditions: 2 mmol of benzophenone, 0.004 mmol precatalyst,
10 mL of iPrOH, reflux (82 °C), 0.008  in KOH, substrate/KOH/
complex ratio of 500:20:1. [b] Catalyst turnover frequency at 20%
conversion. [c] Yield of diphenylmethanol at 24 h of reaction. [d]
No precatalyst was added. [e] 300 equiv. of Hg was added.
Figure 8. Yield of diphenylmethanol against time for the hydrogen-
ation of benzophenone. Conditions: 2 mmol of benzophenone,
10 mL of i-PrOH, reflux (82 °C), 0.004 mmol precatalyst (when ap-
plicable).
Considering these results we decided to study the behav-
iour of our different derivatives with a base concentration
of 0.008  and a substrate/KOH/complex ratio of 500:20:1.
The yields and the turnover frequencies evaluated at 20%
conversion (TOF20) are reflected in Table 4. The conversion
for the TOF number was chosen in order to minimise the
influence on the rate of decreases in substrate concentration
and increases in product concentration. Several clear con-
clusions can be drawn from the analysis of the results. (i)
Better behaviour of the benzene derivatives (those with an
odd number) against p-cymene complexes (even number) is
observed (in some cases the differences are not large). (ii)
The introduction of methyl substituents on the pyrazole
rings has a dramatic and positive effect (compare runs 4/6,
5/7, 11/13 and 12/14). For example, in the case of complexes
4 and 6, the improvement is from 10 to 82% in the product
Figure 9. Yield of diphenylmethanol against time for the hydroge-
nation of benzophenone. Conditions: 2 mmol of benzophenone,
0.004 mmol precatalyst, 10 mL of iPrOH, reflux (82 °C), 0.008 
in KOH, substrate/KOH/complex ratio of 500:20:1.
We subjected complex 7 to the mercury drop test during
yield (see Figure 9 to observe both effects). (iii) The intro- the hydrogenation of benzophenone. Several authors[24]
duction of a phenyl group at the benzyl carbon atom (com- found that the addition of excess metallic mercury (with
pare runs 2/4 and 3/5) also increases the activity of the sys- respect to the metal complex) to the reaction mixture led to
tem. (iv) When the existence of functional groups on this the amalgamation of the surface of a heterogeneous metal
ring is considered, a negative effect of the NH2 (runs 4/15 particle, thus poisoning it, but did not affect a homogen-
and 5/16) or NO2 groups (runs 4/11 and 5/12 for methylated eous catalyst. When we added 300 equiv. of Hg(0) to the
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(Arene)ruthenium(II) Complexes with Bis(pyrazolyl)methane Ligands
FULL PAPER
reaction mixture at t = 0 min, the catalytic system only suf- transfer hydrogenation of benzophenone in the presence of
fered a slight decrease in activity (compare runs 8/9), indi- KOH was studied. The influence of the arene, the func-
cating the existence of a homogeneous system.
tional group on the phenyl ring and the substitution on the
We also carried out a catalytic test with complex 7 pyrazole ring has been evaluated. A marked positive effect
(0.004 mmol), analysing samples at short times of 5, 10, 15, of the methyl groups on the pyrazole rings and of the meth-
30, 45 and 60 min. No induction period was observed. We oxy group on the phenyl ring has been found. The hydro-
also subjected complex 7 to a pretreatment of one hour, genation of benzophenone without the addition of a com-
during which the precatalyst was heated at reflux in the plex in the presence of KOH is possible and the effect of
presence of the base (base:7 = 20:1) prior to the addition the base concentration has been analysed.
of the substrate (2 mmol), and the outcome of the reaction
was the same as that without this treatment.
Experimental Section
The precatalysts are not active in the hydrogenation of
styrene. Thus, they exhibit selectivity towards the ketone
unsaturation.
General: All manipulations were carried out under dry oxygen-free
nitrogen using standard Schlenk techniques. Solvents were distilled
from the appropriate drying agents and degassed before use. Ele-
mental analyses were performed with a Thermo Quest FlashEA
1112 microanalyser. IR spectra were recorded as KBr pellets or
Nujol solutions with a Perkin–Elmer PE 883 IR spectrometer and
on a Shimadzu IRPrestige-21 IR spectrometer equipped with a
Pike Technologies ATR. 1H and 13C{1H} NMR spectra were re-
corded with a Varian Unity 500 spectrometer. Chemical shifts
According to previous mechanistic proposals,[11a–11e] and
considering the formulae and type of ligand present in our
derivatives, the most plausible mechanism is that involving
a monohydride intermediate generated after β elimination
from an isopropoxide complex. In principle, the vacant co-
ordination site necessary for the ketone coordination could
be generated by partial decoordination of the nitrogenated
ligand or by slippage of the arene moiety. Our study of the
isomer interconversion and the fact that the methylated li-
gands that exhibit longer Ru–N distances have much higher
activity point to the former possibility. Transfer of the hy-
dride and reaction with 2-propanol will yield the dibenzyl
alcohol.
(ppm) are relative to TMS (1H, 13C NMR). H-1H COSY spectra:
1
standard pulse sequence with an acquisition time of 0.214 s, pulse
width 10 ms, relaxation delay 1 s, number of scans 16, number of
increments 512. For 1H-13C g-HMBC and g-HMQC spectra the
standard VARIAN pulse sequences were used (VNMR 6.1 C soft-
ware). The spectra were acquired using 7996-Hz (1H) and 25133.5-
Hz (13C) widths; 16 transients of 2048 data points were collected
for each of the 256 increments. NOESY spectra were acquired
using 8000-Hz width; 16 transients of 2048 data points were col-
lected for each of the 256 increments; pulse time of 1 s and mixing
time of 1 s. o-, m- and p- stand for ortho, meta and para. s, d, t and
p stand for singlet, doublet, triplet and apparent for the NMR
More studies concerning the catalytic behaviour of these
complexes are in progress. We will study complexes with the
bpz*PhOCH3 ligand that predictably will give better results
than those reported in Table 4 and we will also consider the
possibility of obtaining ligands that have pyrazoles contain-
ing more bulky substituents. Other parameters such as the
introduction of other functional groups on the phenyl ring
and the use of asymmetric ligands will also be analysed.
resonances. Unless otherwise stated, the 13C{1H} NMR signals are
[13c]
singlets. The ligands bpz*m[18] and bpzmArOCH3
were pre-
pared according to the methods described in the literature. For the
preparation of the ligands bpzmPh and bpz*mPh[17] the ketone
bpz*CO was synthesised as described below.
bpz*CO: 3,5-Dimethylpyrazole (1.5 g, 15.6 mmol) was dissolved in
thf (20 mL) and NEt3 (2.13 mL) was added afterwards. Triphos-
gene, Cl3COCOOCCl3 (772 mg, 2.60 mmol), was dissolved in thf
(20 mL) and the resulting solution was added as quickly as possible
to the initial one. After 16 h of stirring at room temperature, the
white solid formed was filtered off and washed twice with thf. The
thf fractions were combined and the solvent evaporated. The yel-
lowish oil obtained was washed with pentane and a white solid was
formed. The solid was recrystallised from toluene/hexane obtaining
white crystals. Yield 1.4 g (80%).
Conclusions
New bis(pyrazol-1-yl)methane ligands containing dif-
ferent substituents on the central carbon atom have been
synthesised using a new and safer methodology. Ru deriva-
tives of the type [Ru(arene)Cl(NN)]BPh4 (arene = benzene,
p-cymene) have been synthesised from these ligands. The
formation of two isomers is possible depending on the axial
or equatorial disposition of the substituent on this carbon.
The formation of only one isomer (axial) or a mixture of
two (including their ratio) can be rationalised in terms of
steric repulsions (effect of the methyl groups on the pyrazo-
lyl rings or of the arene). A full NMR analysis was per-
formed and a clear effect of the type of isomer on the chem-
ical shifts of certain resonances was found. The structures
of five derivatives were determined by X-ray diffraction. In
four complexes the benzyl substituent is in the axial disposi-
tion and in one case in the equatorial disposition. A rela-
tionship between the dihedral angle formed by the planes
of the two pyrazole rings and the substituent on these rings
bpzCO: The method was similar to that used for bpz*CO. Amounts
were as follows: pyrazole (1 g, 15.6 mmol), NEt3 (2.13 mL) and tri-
phosgene (772 mg, 2.60 mmol). bpzCO was obtained as a white
solid. Yield 948.6 mg (75%).
bpz*mArNO2: bpz*CO (500 mg, 2.29 mmol) and 2-nitrobenzalde-
hyde (346 mg, 2.29 mmol) were mixed in toluene (25 mL). After
refluxing for 24 h, the yellowish solution was evaporated and the
residue was washed with pentane (3ϫ10 mL), obtaining a white
solid of bpz*mArNO2. Yield 506.7 mg (68%). 1H NMR (500 MHz,
CDCl3, 298 K): δ = 2.08 (s, 6 H, Me5-Pz), 2.15 (s, 6 H, Me3-Pz),
5.89 (s, 2 H, H4-Pz), 6.60 (d, J = 7.7 Hz, 1 H, H3-ArNO2), 7.53
(td, J = 7.7, 1.5 Hz, 1 H, H5-ArNO2), 7.57 (td, J = 7.7, 1.5 Hz, 1
was found. The behaviour of the new derivatives in the H, H4-ArNO2), 8.04 (dd, J = 7.7, 1.5 Hz, 1 H, H6-ArNO2), 8.22
Eur. J. Inorg. Chem. 2007, 3961–3973
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3969

B. R. Manzano et al.
(s, 1 H, Hα) ppm. 13C{1H} NMR (125 MHz, CDCl3, 298 K): δ = tion, obtaining a yellow suspension. The solution was partially
FULL PAPER
11.16 (2 C, Me5-Pz), 13.97 (2 C, Me3-Pz), 71.57 (1 C, Cα), 107.22
evaporated up to 5 mL and the solid obtained was filtered off. The
(2 C, C4-Pz), 122.25 (1 C, C6-ArNO2), 128.80 (1 C, C3-ArNO2), yellow solid was washed once with MeOH. The product was recrys-
129.78 (1 C, C5-ArNO2), 131.90 (1 C, C2-ArNO2), 133.86 (1 C, C4- tallised from 1,2-dichloroethane/hexane. Yield 293.5 mg (88%).
ArNO2), 141.17 (2 C, C5-Pz), 148.27 (1 C, C1-ArNO2), 148.76 (2
C45H50BClN4Ru·C2H4Cl2 (893.22): calcd. C 63.20, H 6.09, N 6.27;
found C 63.51, H 6.06, N 6.37. 13C{1H} NMR (125 MHz, CDCl3,
298 K): δ = 11.64 (2 C, Me3-Pz), 16.02 (2 C, Me5-Pz), 18.72 (1 C,
Me-Tol), 22.77 (2 C, Me-iPr), 31.87 (1 C, CH-iPr), 56.01 (1 C, Cα),
81.71 (2 C, CH2/2Ј-p-cym), 84.86 (2 C, CH3/3Ј-p-cym), 99.74 (1 C,
C4-p-cym), 107.38 (1 C, C1-p-cym), 109.75 (2 C, C4-Pz), 122.29 [4
C, Cp-Ph(BPH4)], 125.96 [8 C, Cm-Ph(BPh4)], 136.52 [8 C,
Co-Ph(BPh4)], 143.32 (2 C, C5-Pz), 156.86 (2 C, C3-Pz), 164.32 [q,
C, C3-Pz) ppm. IR (KBr): ν = 1563 (CN); 1528, 1360, 1317 (NO)
˜
cm–1.
bpzmArNO2: The method was similar to that used for
bpz*mArNO2. Amounts were as follows: bpzCO (300 mg,
1.85 mmol) and 2-nitrobenzaldehyde (280 mg, 1.85 mmol). Yield
382.3 mg (62%). 1H NMR (500 MHz, CDCl3, 298 K): δ = 6.38 (pt,
J = 2.1 Hz, 2 H, H4-Pz), 6.71 (dd, J = 7.3, 1.7 Hz, 1 H, H3-ArNO2),
7.52 (d, J = 2.2 Hz, 2 H, H5-Pz), 7.57 (td, J = 7.6, 1.7 Hz, 1 H,
H5-ArNO2), 7.62 (td, J = 7.6, 1.7 Hz, 1 H, H4-ArNO2), 7.63 (d, J
JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh )] ppm. IR: ν = 1560 (CN)
˜
4
B
cm–1.
= 1.7 Hz, 2 H, H3-Pz), 8.11 (dd, J = 7.6, 1.9 Hz, 1 H, H6-Ar NO2), [RuCl(benzene)(bpz*mPh)][BPh4] (3): The method was similar to
8.52 (s, 1 H, Hα) ppm. 13C{1H} NMR (125 MHz, CDCl3, 298 K): that used for complex 1. Amounts were as follows:
δ = 74.42 (1 C, Cα), 107.42 (2 C, C4-Pz), 125.64 (1 C, C6-ArNO2), [RuCl2(C6H6)(CH3CN)] (93 mg, 0.32 mmol) and bpz*m (89.7 mg,
129.40 (1 C, C3-ArNO2), 130.58 (1 C, C5-ArNO2), 130.92 (2 C, C5- 0.32 mmol). Complex 3 was obtained as a yellowish solid. The
Pz), 131.79 (1 C, C2-ArNO2), 134.10 (1 C, C4-ArNO2), 141.44 (2
product was recrystallised from 1,2-dichloroethane/hexane. Yield
221.5 mg (85%). C47H46BClN4ORu·0.5C2H4Cl2 (863.73): calcd. C
66.75, H 5.60, N 6.49; found C 66.45, H 5.66, N 7.20. 13C{1H}
NMR (125 MHz, CD3COCD3, 298 K): δ = 10.98 (2 C, Me5-Pz),
16.10 (2 C, Me3-Pz), 68.78 (1 C, Cα), 86.31 (6 C, C-benzene), 109.61
(2 C, C4-Pz), 121.63 [4 C, Cp-Ph(BPh4)], 125.41 [8 C, Cm-Ph(BPh4)],
125.56 (2 C, Co-Ph), 130.25 (1 C, Cp-Ph), 130.282 (2 C, Cm-Ph),
136.38 [8 C, Co-Ph(BPh4)], 136.757 (1 C, C1-Ph), 146.48 (2 C, C5-
C, C3-Pz), 147.52 (1 C, C1-ArNO ) ppm. IR (KBr): ν = 1580 (CN);
˜
2
1526, 1350, 1312 (NO) cm–1.
bpz*mArNH2: bpz*mArNO2 (745.1 mg, 2.29 mmol) was solved in
toluene (30 mL) in a Fischer-Porter tube. A suspension of Pd/C
(10%) catalyst (200 mg) in toluene (10 mL) was added to the initial
solution. When the system was under dry oxygen-free nitrogen, hy-
drogen was introduced under pressure (about 3 kg·cm–2). After
5.5 h of reaction at room temperature, the suspension was filtered
off in a column filled with Kieselguhr. The solution was evapo-
rated, obtaining a bright yellow oil, which was left under vacuum
overnight, and a pale yellow solid was obtained. After recrystalli-
sation in toluene/pentane, colourless crystals were obtained. Yield:
Pz), 157.86 (2 C, C3-Pz), 164.31 [q, JC–11 = 49.4 Hz, 4 C, Cipso
-
B
Ph(BPh )] ppm. IR: ν = 1558 (CN) cm–1.
˜
4
[RuCl(p-cymene)(bpz*mPh)][BPh4] (4): The method was similar to
that used for complex 2. Amounts were as follows: [RuCl2(p-cy-
mene)]2 (128 mg, 0.21 mmol) and bpz*mPh (117.8 mg, 0.42 mmol).
Complex 4 was obtained as an orange solid, which was washed
once with MeOH. Yield 325.3 mg (89%). C51H54BClN4Ru·CH3OH
(902.40): C 69.21, H 6.48, N 6.21; found C 69.13, H 6.45, N 6.23.
1
491.8 mg (90%). H NMR (500 MHz, CDCl3, 298 K): δ = 2.14 (s,
6 H, Me5-Pz), 2.22 (s, 6 H, Me3-Pz), 3.51 (br. s, 2 H, NH2), 5.87
(s, 2 H, H4-Pz), 6.42 (d, J = 7.8 Hz, 1 H, H3-ArNH2), 6.65 (d, J =
7.3 Hz, 1 H, H6-ArNH2), 6.68 (t, J = 7.6 Hz, 1 H, H4-ArNH2), 13C{1H} NMR (125 MHz, CD3COCD3, 298 K): δ = 11.23 (2 C,
7.13 (t, J = 7.1 Hz, 1 H, H5-ArNH2), 7.40 (s, 1 H, Hα) ppm.
13C{1H} NMR (125 MHz, CDCl3, 298 K): δ = 11.93 (2 C, Me5-
Pz), 14.08 (2 C, Me3-Pz), 72.58 (1 C, Cα), 107.19 (2 C, C4-Pz),
Me5-Pz), 16.44 (2 C, Me3-Pz), 17.63 (1 C, Me-Tol), 21.76 (1 C, CH-
iPr), 22.38 (2 C, Me-iPr), 66.62 (1 C, Cα), 82.20 (2 C, CH2/2Ј-p-
cym), 84.42 (2 C, CH3/3Ј-p-cym), 101.97 (1 C, C4-p-cym), 107.23 (1
116.48 (1 C, C6-ArNH2), 118.63 (1 C, C4-ArNH2), 121.53 (1 C, C2- C, C1-p-cym), 109.93 (2 C, C4-Pz), 121.58 [4 C, Cp-Ph(BPh4)],
ArNH2), 127.64 (1 C, C3-ArNH2), 129.88 (1 C, C5-ArNH2), 141.43
125.34 [8 C, Cm-Ph(BPh4)], 126.23 (2 C, Co-Ph), 130.13 (2 C,
(2 C, C5-Pz), 144.49 (1 C, C1-ArNH2), 148.96 (2 C, C3-Pz) ppm. Cm-Ph), 130.35 (1 C, Cp-Ph), 135.99 (1 C, C1-Ph), 136.41 [8 C,
IR (KBr): ν = 3395, 3312 (NH ); 1554 (CN) cm–1.
Co-Ph(BPh4)], 146.55 (2 C, C5-Pz), 157.87 (2 C, C3-Pz), 164.32 [q,
JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh )] ppm. IR: ν = 1566 (CN)
˜
2
˜
4
B
[RuCl(benzene)(bpz*m)][BPh4] (1): [RuCl2(C6H6)(CH3CN)] (93 mg,
0.32 mmol) and bpz*m (65.4 mg, 0.32 mmol) were mixed in MeOH
(10 mL). After stirring for 12 h, a solution of NaBPh4 (200 mg,
0.6 mmol) in MeOH (10 mL) was added to the initial orange solu-
tion, changing the colour to yellow. After 30 min, the solution was
partially evaporated up to 5 mL and the solid obtained was filtered
cm–1.
[RuCl(benzene)(bpzmPh)][BPh4] (5): The method was similar to that
used for complex 2. Amounts were as follows:
[RuCl2(C6H6)(CH3CN)] (37.8 mg, 0.13 mmol) and bpzmPh
(29.1 mg, 0.25 mmol). The yellow solid obtained was washed once
off. The light yellow solid was washed once with MeOH. The prod- with MeOH. The product was recrystallised from 1,2-dichloro-
uct was recrystallised from 1,2-dichloroethane/hexane. Yield
210.2 mg (89%). C41H42BClN4Ru·C2H4Cl2 (837.11): calcd.
ethane/hexane. Yield: 161.1 mg (85%). C43H38BClN4Ru·
0.5C2H4Cl2 (807.62): calcd. C 65.44, H 4.99, N 6.94; found C 65.88,
H 4.88, N 7.08. 13C{1H} NMR (125 MHz, CD3COCD3, 298 K): δ
= 75.26 (1 C, Cα), 86.48 (6 C, C-benzene), 108.80 (2 C, C4-Pz),
121.62 [4 C, Cp-Ph(BPh4)], 125.36 (2 C, Co-Ph), 125.42 [8 C, Cm-
Ph(BPh4)], 129.97 (2 C, Cm-Ph), 130.38 (1 C, Cp-Ph), 136.39 [8 C,
Co-Ph(BPh4)], 130.67 (2 C, C5-Pz), 150.98 (2 C, C3-Pz), 164.29 [q,
C
61.70, H 5.54, N 6.69; found C 61.41, H 5.41, N 6.94. 13C{1H}
NMR (125 MHz, CDCl3, 298 K): δ = 11.38 (2 C, Me5-Pz), 15.76
(2 C, Me3-Pz), 55.67 (1 C, Cα), 85.46 (6 C, C-benzene), 109.35 (2
C, C4-Pz), 122.11 [4 C, Cp-Ph(BPh4)], 125.81 [8 C, Cm-Ph(BPh4)],
136.19 [8 C, Co-Ph(BPh4)], 142.99 (2 C, C5-Pz), 156.28 (2 C, C3-
Pz), 164.31 [q, JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh )] ppm. IR: ν
JC–11 = 49.4 Hz, 4C, Cipso-Ph(BPh )] ppm. IR: ν = 1577 (CN)
˜
4
B
˜
4
B
= 1558 (CN) cm–1.
cm–1.
[RuCl(p-cymene)(bpz*m)][BPh4] (2): [RuCl2(p-cymene)]2 (128 mg,
0.21 mmol) and bpz*m (85.8 mg, 0.42 mmol) were stirred in MeOH
[RuCl(p-cymene)(bpzmPh)][BPh4] (6): The method was similar to
that used for complex 2. Amounts were as follows: [RuCl2(p-cy-
(10 mL) for 12 h. Afterwards, a solution of MeOH (10 mL) with mene)]2 (36.7 mg, 0.06 mmol) and bpzmPh (29.1 mg, 0.13 mmol)
NaBPh4 (200 mg, 0.6 mmol) was added to the initial reddish solu- in MeOH (5 mL). Complex 6 was obtained as a light yellow solid,
3970
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 3961–3973

(Arene)ruthenium(II) Complexes with Bis(pyrazolyl)methane Ligands
FULL PAPER
which was washed once with MeOH. Yield: 95.3 mg (90%).
C47H46BClN4Ru (814.25): calcd. C 69.33, H 5.69, N 6.88; found
Ph(BPh4)], 125.22 (1 C, C6-ArNO2), 125.35 [8 C, Cm-Ph(BPh4)],
128.86 (1 C, C2-ArNO2), 129.55 (1 C, C3-ArNO2), 132.36 (1 C, C4-
C 69.42, H 5.61, N 6.92. 13C{1H} NMR (125 MHz, CD3COCD3, ArNO2), 133.07 (1 C, C5-ArNO2), 136.39 [8 C, Co-Ph(BPh4)],
298 K): δ = 17.80 (1 C, Me-Tol), 21.79 (1 C, CH-iPr), 22.07 (2 C,
Me-iPr), 75.29 (1 C, Cα), 80.77 (2 C, CH3/3Ј-p-cym), 88.75 (2 C,
CH2/2Ј-p-cym), 101.92 (1 C, C4-p-cym), 104.32 (1 C, C1-p-cym),
108.99 (2 C, C4-Pz), 121.58 [4 C, Cp-Ph(BPH4)], 125.34 [8 C, Cm-
Ph(BPh4)], 125.70 (2 C, Co-Ph), 130.05 (2 C, Cm-Ph), 130.49 (1 C,
Cp-Ph), 136.41 [8 C, Co-Ph(BPh4)], 137.65 (2 C, C5-Pz), 149.96 (2
149.29 (1 C, C1-ArNO2), 164.29 [q, JC–11 = 49.4 Hz, 4 C, Cipso
-
B
Ph(BPh )] ppm. IR (Nujol): ν = 1563 (CN); 1542 (NO) cm–1.
˜
4
[RuCl(p-cymene)(bpz*mArNO2)][BPh4] (10): The method was sim-
ilar to that used for complex 2. Amounts were as follows: [RuCl2(p-
cymene)]2 (76.5 mg, 0.125 mmol) and bpz*mArNO2 (81.3 mg,
0.25 mmol) in MeOH (10 mL). Complex 10 was obtained as a
cream-coloured solid. The product was recrystallised from 1,2-
dichloroethane/hexane (X-ray crystals). Yield: 178.5 mg (78%).
C51H53BClN5O2Ru·0.5C2H4Cl2 (964.84): calcd. C 64.73, H 5.75, N
7.26; found C 64.76, H 5.83, N 7.21. 13C{1H} NMR (CDCl3,
C, C3-Pz), 164.32 [q, JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh4)] ppm.
B
IR: ν = 1577 (CN) cm–1.
˜
[RuCl(benzene)(bpzmArOCH3)][BPh4] (7): The method was similar
to that used for complex 1. Amounts were as follows:
[RuCl2(C6H6)(CH3CN)] (37.8 mg, 0.13 mmol) and bpzmArOCH3 125 MHz, 298 K): δ = 12.00 (2 C, Me5-Pz), 17.35 (2 C, Me3-Pz),
(33.1 mg, 0.13 mmol) in MeOH (5 mL). Complex 7 was obtained 18.51 (1 C, Me-Tol), 23.06 (2 C, Me-iPr), 31.11 (1 C, CH-iPr), 65.22
as a yellow solid. Yield: 86.6 mg (83%). Ratio of isomers A/B =
4.8:1. C44H40BClN4ORu·0.5C2H4Cl2 (837.65): calcd. C 64.53, H
5.05, N 6.69; found C 64.58, H 5.09, N 6.58. Crystals for the X-
ray structure determination were obtained from 1,2-dichloro-
ethane/hexane. Isomer A: 13C{1H} NMR (CD3COCD3, 125 MHz,
298 K): δ = 55.51 (1 C, Me-ArOCH3), 73.30 (1 C, Cα), 86.61 (6 C,
(1 C, Cα), 81.91 (2 C, CH2/2Ј-p-cym), 83.35 (2 C, CH3/3Ј-p-cym),
103.08 (1 C, C4-p-cym), 106.49 (1 C, C1-p-cym), 110.69 (2 C, C4-
Pz), 121.67 [4 C, Cp-Ph(BPh4)], 124.81 (1 C, C6-ArNO2), 125.47 [8
C, Cm-Ph(BPh4)], 126.61 (1 C, C2-ArNO2), 129.16 (1 C, C3-
ArNO2), 132.62 (1 C, C4-ArNO2), 133.54 (1 C, C5-ArNO2), 136.11
[8 C, Co-Ph(BPh4)], 146.34 (2 C, C5-Pz), 148.35 (1 C, C1-ArNO2),
C-benzene), 108.12 (2 C, C4-Pz); 121.60 (4 C, Cp-Ph(BPh4)), 125.36 159.21 (1 C, C3-Pz), 163.89 [q, JC–11 = 49.4 Hz, 4 C, Cipso
-
B
[8 C, Cm-Ph(BPh4)], 127.96 (1 C, C3-ArOCH3), 136.39 [8 C, Co-
Ph(BPh4)], 137.89 (2 C, C5-Pz), 150.53 (2 C, C3-Pz), 164.29 [q,
Ph(BPh )] ppm. IR (Nujol): ν = 1562 (CN); 1531 (NO) cm–1.
˜
4
[RuCl(benzene)(bpzmArNO2)][BPh4] (11): The method was similar
to that used for complex 1. Amounts were as follows:
[RuCl2(C6H6)(CH3CN)] (72.8 mg, 0.25 mmol) and bpzmArNO2
(67.3 mg, 0.25 mmol) in MeOH (10 mL). Complex 11 was obtained
as a pale yellow solid. Ratio of isomers A/B = 4.2:1. The product
was recrystallised from 1,2-dichloroethane/hexane. Yield: 162.6 mg
(81%). C43H37BClN5O2Ru·0.5C2H4Cl2 (852.62): calcd. C 61.98, H
4.61, N 8.21; found C 62.32, H 4.34, N 8.18. Isomer A: 13C{1H}
NMR (125 MHz, CD3COCD3, 298 K): δ = 72.41 (1 C, Cα), 86.41
(6 C, C-benzene), 108.98 (2 C, C4-Pz), 121.61 [4 C, Cp-Ph(BPh4)],
125.36 [8 C, Cm-Ph(BPh4)], 125.49 (1 C, C6-ArNO2), 128.61 (1 C,
C2-ArNO2), 129.60 (1 C, C3-ArNO2), 132.60 (1 C, C4-ArNO2),
133.19 (1 C, C5-ArNO2), 136.39 [8 C, Co-Ph(BPh4)], 139.07 (2 C,
C5-Pz), 148.85 (1 C, C1-ArNO2), 151.99 (2 C, C3-Pz), 164.56 [q,
JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh4)] ppm. Isomer B: 13C{1H}
B
NMR (CD3COCD3, 125 MHz, 298 K): δ = 87.04 (6 C, C-benzene),
121.60 [4 C, Cp-Ph(BPh4)], 125.36 [8 C, Cm-Ph(BPh4)], 136.39 [8 C,
Co-Ph(BPh4)], 164.29 [q, JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh4)]
B
ppm. IR: ν = 1580 (CN) cm–1.
˜
[RuCl(p-cymene)(bpzmArOCH3)][BPh4] (8): The method was sim-
ilar to that used for complex 2. Amounts were as follows: [RuCl2(p-
cymene)]2 (36.7 mg, 0.06 mmol) and bpzmArOCH3 (33.1 mg,
0.13 mmol) in MeOH (5 mL). Complex 8 was obtained as a yellow
solid. Yield: 56.1 mg (78%). Ratio of isomers A/B = 1.1:1.
C48H48BClN4ORu (844.28): calcd. C 68.29, H 5.73, N 6.64; found
C 68.25, H 5.77, N 6.68. Crystals for the X-ray structure determi-
nation were obtained from 1,2-dichloroethane/pentane. Isomer A:
13C{1H} NMR (125 MHz, CD3COCD3, 298 K): δ = 17.73 (1 C, JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh4)] ppm. Isomer B: 13C{1H}
B
Me-Tol), 22.25 (2 C, Me-iPr), 31.14 (1 C, CH-iPr), 55.75 (1 C, Me-
NMR (125 MHz, CD3COCD3, 298 K): δ = 72.00 (1 C, Cα), 87.08
ArOCH3), 73.73 (1 C, Cα), 84.77 (2 C, CH2/2Ј-p-cym), 85.94 (2 C, (6 C, C-benzene), 108.47 (2 C, C4-Pz), 121.61 [4 C, Cp-Ph(BPh4)],
CH3/3Ј-p-cym), 105.64 (1 C, C1-p-cym), 108.65 (2 C, C4-Pz), 112.77 125.36 [8 C, Cm-Ph(BPh4)], 126.96 (1 C, C6-ArNO2), 133.64 (1 C,
(1 C, C6-ArOCH3), 121.43 (1 C, C4-ArOCH3), 122.02 [4 C, Cp- C3-ArNO2), 134.15 (1 C, C5-ArNO2), 135.23 (1 C, C4-ArNO2),
Ph(BPh4)], 125.75 [8 C, Cm-Ph(BPh4)], 128.61 (1 C, C3-ArOCH3),
133.05 (1 C, C5-ArOCH3), 136.84 [8 C, Co-Ph(BPh4)], 138.39 (2 C,
C5-Pz), 150.34 (2 C, C3-Pz), 158.23 (1 C, C1-ArOCH3), 164.29 [q,
135.50 (2 C, C5-Pz), 136.39 [8 C, Co-Ph(BPh4)], 149.54 (2 C, C3-Pz),
164.56 [q, JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh )] ppm. IR (Nujol): ν
˜
4
B
= 1579 (CN); 1530 (NO) cm–1.
JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh4)] ppm. Isomer B: 13C{1H}
B
[RuCl(p-cymene)(bpzmArNO2)][BPh4] (12): The method was sim-
ilar to that used for complex 2. Amounts were as follows: [RuCl2(p-
cymene)]2 (76.5 mg, 0.125 mmol) and bpzmArNO2 (67.3 mg,
0.25 mmol) in MeOH (10 mL). Complex 12 was obtained as a yel-
lowish orange solid, as a mixture of the isomers. Yield: 139.6 mg
(65%). Ratio of isomers A/B = 1.2:1. The product was recrystal-
NMR (125 MHz, CD3COCD3, 298 K): δ = 18.37 (1 C, Me-Tol),
22.21 (2 C, Me-iPr), 31.72 (1 C, CH-iPr), 85.46 (br. s, 4 C, CH2/2Ј
,
CH3/3Ј-p-cym), 108.69 (2 C, C4-Pz), 122.02 [4 C, Cp-Ph(BPh4)],
125.75 [8 C, Cm-Ph(BPh4)], 135.48 (br. s, 3 C, C5-ArOCH3, C5-Pz),
136.84 [9 C, Co-Ph(BPh4), C6-ArOCH3], 164.29 [q, JC–11
=
B
49.4 Hz, 4 C, Cipso-Ph(BPh )] ppm. IR: ν = 1580 (CN) cm–1.
˜
4
lised
from
1,2-dichloroethane/hexane
(X-ray
crystals).
[RuCl(benzene)(bpz*mArNO2)][BPh4] (9): The method was similar
to that used for complex 1. Amounts were as follows:
[RuCl2(C6H6)(CH3CN)] (72.8 mg, 0.25 mmol) and bpz*mArNO2
(81.3 mg, 0.25 mmol) in MeOH (10 mL). Complex 9 was obtained
as a bright yellow solid. The product was recrystallised from 1,2-
dichloroethane/hexane (X-ray crystals). Yield: 159.0 mg (74%).
C47H45BClN5O2Ru (859.25): calcd. C 65.70, H 5.28, N 8.15; found
C47H45BClN5O2Ru (859.25): calcd. C 65.70, H 5.28, N 8.15; found
C 65.62, H 5.19, N 8.21. Isomer A: 13C{1H} NMR (125 MHz,
CD3COCD3, 298 K): δ = 17.70 (1 C, Me-Tol), 21.97 (2 C, Me-iPr),
30.51 (1 C, CH-iPr), 72.25 (1 C, Cα), 81.26 (2 C, CH2/2Ј-p-cym),
88.13 (2 C, CH3/3Ј-p-cym), 102.52 (1 C, C4-p-cym), 103.69 (1 C, C1-
p-cym), 109.16 (2 C, C4-Pz), 121.61 [4 C, Cp-Ph(BPh4)], 125.47 [8
C, Cm-Ph(BPh4)], 125.52 (1 C, C6-ArNO2), 128.52 (1 C, C2-
C 65.79, H 5.22, N 8.18. 13C{1H} NMR (125 MHz, CDCl3, ArNO2), 129.80 (1 C, C3-ArNO2), 132.79 (1 C, C4-ArNO2), 133.48
298 K): δ = 11.17 (2 C, Me3-Pz), 16.32 (2 C, Me5-Pz), 66.35 (1 C, (1 C, C5-ArNO2), 136.38 [8 C, Co-Ph(BPh4)], 139.04 (2 C, C5-Pz),
Cα), 86.01 (6 C, C-benzene), 110.14 (2 C, C4-Pz), 121.60 [4 C, Cp-
151.04 (2 C, C3-Pz), 149.05 (1 C, C1-ArNO2), 164.29 [q, JC–11
=
B
Eur. J. Inorg. Chem. 2007, 3961–3973
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3971

B. R. Manzano et al.
FULL PAPER
49.4 Hz, 4 C, Cipso-Ph(BPh4)] ppm. Isomer B: 13C{1H} NMR Prismatic crystals of complexes 9, 10·0.5C2H4Cl2 and 12A were se-
(125 MHz, CD3COCD3, 298 K): δ = 17.93 (1 C, Me-Tol), 21.97 (2 lected and mounted on Bruker SMART-CCD area dif-
a
C, Me-iPr), 30.97 (1 C, CH-iPr), 71.93 (1 C, Cα), 83.39 (2 C, fractometer. Intensities were collected with graphite-monochro-
CH2/2Ј-p-cym), 87.03 (2 C, CH3/3Ј-p-cym), 102.58 (1 C, C4-p-cym), mated Mo-Kα radiation (λ = 0.71073 Å). Lorentz polarisation and
105.32 (1 C, C1-p-cym), 108.64 (2 C, C4-Pz), 121.61 [4 C, Cp-
Ph(BPh4)], 121.79 (1 C, C2-ArNO2), 125.47 [8 C, Cm-Ph(BPh4)],
absorption corrections were made.[26] The structures were solved by
direct methods, using the SHELXS computer program[28] and re-
126.88 (1 C, C6-ArNO2), 133.86 (1 C, C3-ArNO2), 134.23 (1 C, C4- fined by full-matrix least-squares method with the SHELX97 com-
ArNO2), 135.16 (1 C, C5-ArNO2), 135.77 (2 C, C5-Pz), 136.38 [8
puter program.[28] All hydrogen atoms were computed and refined
C, Co-Ph(BPh4)], 148.88 (2 C, C3-Pz), 150.76 (1 C, C1-ArNO2), using a riding model.
164.29 [q, JC–11 = 49.4 Hz, 4 C, Cipso-Ph(BPh )] ppm. IR: ν = 1580
˜
4
B
CCDC-631606 to -631610 contain the supplementary crystallo-
graphic data for complexes 7A·0.5C2H4Cl2, 8B, 9, 10·0.5C2H4Cl2
and 12A. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(CN), 1533 (NO) cm–1.
[RuCl(benzene)(bpz*mArNH2)][BPh4] (13): The method was similar
to that used for complex 1. Amounts were as follows:
[RuCl2(C6H6)(CH3CN)] (72.8 mg, 0.25 mmol) and bpz*mArNH2
(73.8 mg, 0.25 mmol) in MeOH (10 mL). Complex 13 was obtained
as a yellow solid. The product was recrystallised from 1,2-dichloro-
ethane/hexane. Yield: 165.8 mg (80%). C47H47BClN5Ru·
0.5C2H4Cl2 (878.75): calcd. C 65.61, H 5.62, N 7.97; found C 65.88,
H 5.34, N 8.04. 13C{1H} NMR (125 MHz, CDCl3, 298 K): δ =
11.48 (2 C, Me3-Pz), 16.29 (2 C, Me5-Pz), 67.97 (1 C, Cα), 86.28 (6
C, C-benzene), 109.87 (2 C, C4-Pz), 119.08 (1 C, C4-ArNH2),
119.35 (1 C, C6-ArNH2), 121.45 [4 C, Cp-Ph(BPh4)], 125.21 [8 C,
Cm-Ph(BPh4)], 127.64 (1 C, C3-ArNH2), 130.98 (1 C, C5-ArNH2),
136.24 [8 C, Co-Ph(BPh4)], 145.65 (1 C, C1-ArNH2), 145.88 (2 C,
Supporting Information (see footnote on the first page of this arti-
cle): Tables S1 and S2 contain the 1H NMR spectroscopic data and
the results of the catalytic tests at different times, respectively.
Acknowledgments
Financial support from the Junta de Castilla-La Mancha-FEDER
Funds (PBI-05-003) and the Spanish DGES/MCyT (CTQ2005-
01430/BQU) is acknowledged.
C5-Pz), 157.97 (2 C, C3-Pz), 164.07 [q, JC–11 = 49.4 Hz, 4 C, Cipso
-
B
Ph(BPh )] ppm. IR: ν = 1562 (CN), 3464 (NH ) cm–1.
˜
4
2
[1] S. Trofimenko, Scorpionates, The Coordination Chemistry of
Polypyrazolylborate Ligands, Imperial College Press, London,
1999.
[RuCl(p-cymene)(bpz*mArNH2)][BPh4] (14): The method was sim-
ilar to that used for complex 2. Amounts were as follows: [RuCl2(p-
cymene)]2 (76.5 mg, 0.125 mmol) and bpz*mArNH2 (73.8 mg,
0.25 mmol) in MeOH (10 mL). Complex 14 was obtained as a red-
dish orange solid. Yield: 157.16 mg (71%). C51H55BClN5Ru·
1.5CH3OH (933.44): calcd. C 67.56, H 6.59, N 7.50; found C 67.55,
H 6.40, N 7.14. 13C{1H} NMR (125 MHz, CDCl3, 298 K): δ =
12.42 (2 C, Me5-Pz), 17.27 (2 C, Me3-Pz), 18.43 (1 C, Me-Tol),
23.22 (2 C, Me-iPr), 30.79 (1 C, CH-iPr), 67.28 (1 C, Cα), 83.01 (2
C, CH2/2Ј-p-cym), 83.81 (2 C, CH3/3Ј-p-cym), 102.14 (1 C, C4-p-
cym), 107.56 (1 C, C1-p-cym), 110.76 (2 C, C4-Pz), 118.26 (1 C, C2-
ArNH2), 119.78 (1 C, C4-ArNH2), 120.27 (1 C, C6-ArNH2), 122.09
[4 C, Cp-Ph(BPh4)], 125.86 [8 C, Cm-Ph(BPh4)], 127.56 (1 C, C3-
ArNH2), 132.16 (1 C, C5-ArNH2), 136.54 [8 C, Co-Ph(BPh4)],
145.30 (1 C, C1-ArNH2), 145.06 (2 C, C5-Pz), 158.00 (2 C, C3-Pz),
[2] a) A. Caballero, M. C. Carrión, G. Espino, F. A. Jalón, B. R.
Manzano, Polyhedron 2004, 23, 361–371; b) D. C. Wilson, J. H.
Nelson, J. Organomet. Chem. 2003, 682, 272–289; c) B. A. Mes-
serle, V. Tolhurst, P. Turner, Eur. J. Inorg. Chem. 2003, 2, 293–
300; d) C. Zuccaccia, G. Bellachioma, G. Cardaci, A. Mac-
chioni, J. Am. Chem. Soc. 2001, 123, 11020–11028; e) M. H.
Huynh, J. M. Lasker, M. Wetzler, B. Mort, L. Szczepura, L. M.
Witham, J. M. Cintron, A. C. Marschilok, L. J. Ackerman,
R. K. Castellano, D. L. Jameson, M. R. Churchill, A. J. Jircit-
ano, K. J. Takeuchi, J. Am. Chem. Soc. 2001, 123, 8780–8784;
f) L. D. Field, B. A. Messerle, L. Soler, I. E. Buys, T. W. Ham-
bley, J. Chem. Soc. Dalton Trans. 2001, 13, 1959–1965; g) M.
Yamaguchi, T. Iida, T. Yamagishi, Inorg. Chem. Commun. 1998,
1, 299–301; h) A. Macchioni, G. Bellachioma, G. Cardaci, V.
Gramlich, H. Rueegger, S. Terenzi, L. M. Venanzi, Organome-
tallics 1997, 16, 2139–2145; i) F. A. Jalón, A. Otero, A. Rodríg-
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B
ν = 1562 (CN), 3467 (NH ) cm–1.
˜
2
Hydrogen-Transfer Catalysis: A typical procedure for the catalytic
hydrogen-transfer reaction is as follows. A mixture of benzophe-
none (368.1 mg, 2 mmol), KOH (10 mL, 0.008  in iPrOH) and the
catalyst (0.004 mmol) was heated to reflux under nitrogen. At the
desired reaction times, aliquots were extracted from the reaction
1
vessel, obtaining the yields by H NMR spectroscopy.
X-ray Crystallography: A summary of crystal data collection and
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Eur. J. Inorg. Chem. 2007, 3961–3973

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Received: March 7, 2007
Published Online: July 6, 2007
Eur. J. Inorg. Chem. 2007, 3961–3973
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3973