Half-sandwich ruthenium(ii) picolyl-nhc complexes: Synthesis, characterization, and catalytic activity in transfer hydrogenation reactions

Article abstract of DOI:10.1021/om200665f

Pentamethylcyclopentadienyl ruthenium(II) complexes with picolyl-functionalized N-heterocyclic carbenes [(η⁵-C ₅Me₅)-Ru(L)(CH₃CN)][PF₆] (L = 3-methyl-1-(2-picolyl)imidazol-2-ylidene (1a), 3-isopropyl-1-(2-picolyl) imidazol-2-ylidene (1b), 3-phenyl-1-(2-picolyl)imidazol-2-ylidene (1c), 3-mesityl-1-(2-picolyl)imidazol-2-ylidene (1d), 3-methyl-1-(2-picolyl) benzoimidazol-2-ylidene (1e), 3-methyl-1-(2-picolyl)-4,5-dichloroimidazol-2- ylidene (1f)) have been synthesized and characterized. Compounds 1a,b were recrystallized as BAr₄ F salts (anion BAr₄ ^F- = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate), giving 2a,b. X-ray crystal structures of the acetonitrile adduct 2a and the dioxygen compound 2b are also reported. Furthermore, carbonyl derivatives 3a-f have been prepared, characterized, and used to study the donor properties of the picolylcarbene ligands(l) via infrared spectroscopy. Compounds 1a-f show catalytic activity in transfer hydrogenation of ketones. Notably, complex 1a was found to be a very efficient and versatile catalyst toward transfer hydrogenation of a wide range of ketones and imines.

Full text of DOI:10.1021/om200665f

ARTICLE
pubs.acs.org/Organometallics
Half-Sandwich Ruthenium(II) Picolyl-NHC Complexes:
Synthesis, Characterization, and Catalytic Activity in Transfer
Hydrogenation Reactions
Francys E. Fernꢀandez, M. Carmen Puerta,* and Pedro Valerga*
Departamento de Ciencia de los Materiales e Ingeniería Metalꢀurgica y Química Inorgꢀanica, Facultad de Ciencias, Universidad de Cꢀadiz,
11510 Puerto Real, Cꢀadiz, Espa~na
S Supporting Information
b
ABSTRACT: Pentamethylcyclopentadienyl ruthenium(II) com-
plexes with picolyl-functionalized N-heterocyclic carbenes [(η5-C5Me5)-
Ru(L)(CH3CN)][PF6] (L = 3-methyl-1-(2-picolyl)imidazol-2-ylidene
(1a), 3-isopropyl-1-(2-picolyl)imidazol-2-ylidene (1b), 3-phenyl-
1-(2-picolyl)imidazol-2-ylidene (1c), 3-mesityl-1-(2-picolyl)imidazol-
2-ylidene (1d), 3-methyl-1-(2-picolyl)benzoimidazol-2-ylidene (1e),
3-methyl-1-(2-picolyl)-4,5-dichloroimidazol-2-ylidene (1f)) have been
synthesized and characterized. Compounds 1a,b were recrystallized as
BAr4F salts (anion BAr4Fꢀ = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate), giving 2a,b. X-ray crystal structures of the acetonitrile
adduct 2a and the dioxygen compound 2b are also reported. Furthermore, carbonyl derivatives 3aꢀf have been prepared,
characterized, and used to study the donor properties of the picolylcarbene ligands (L) via infrared spectroscopy. Compounds 1aꢀf
show catalytic activity in transfer hydrogenation of ketones. Notably, complex 1a was found to be a very efficient and versatile
catalyst toward transfer hydrogenation of a wide range of ketones and imines.
’ INTRODUCTION
complexes bearing monodentate NHCs proven to be active toward
olefin metathesis and racemization of chiral alcohols.22 In addition,
the synthesis of Cp ruthenium complexes (Cp = cyclopentadienyl)
with NHCs which showed catalytic activity for alkyne dimerization
has been reported.23 Recently, Peris reported the synthesis and
catalytic activity of two complexes of ruthenium with Cp-NHC-
functionalized ligands.24 Jin et al. synthesized a half-sandwich
ruthenium containing 1,2-dichalcogenolato-1,2-dicarba-closo-dode-
carborane and a picolyl-NHC ligand noncoordinated by the pyridyl
arm (Figure 1).25 However, to the best of our knowledge there are
no reports of cyclopentadienyl Ru picolyl-NHC complexes.
Transfer hydrogenation reactions of CdO and CdNR groups
using metal complexes as catalysts have been extensively studied
and continue to generate a high degree of interest, given the need
to develop environmentally friendly and simple processes.26
NHC complexes of iridium,27 rhodium,28 and ruthenium29 have
demonstrated good activity in those reactions, particularly show-
ing significant applications in asymmetric reductions30 and
racemization of chiral alcohols.31 Recently, Morris and co-work-
ers reported the hydrogenation of substituted acetophenones
using a pentamethylcyclopentadienyl ruthenium(II) NHC
complex.32
In recent years, N-heterocyclic carbenes (NHCs) have been
widely used in organometallic chemistry as an alternative to well-
known phosphine ligands for the synthesis of homogeneous
catalysts.1 Many efforts have been placed in the design of new
NHC ligands to tune their steric and electronic properties toward
enhancing the catalytic activity of their complexes. NHCs
functionalized with an additional donor group have become an
important group of ligands due to the potential hemilability of
the new donor group, capable of reversible dissociation from the
metal center. Many reports have been published with phos-
phine,2 pyrimidine,3 ether,4 thioether,5 carboxylate,6 indenyl,7
oxazoline,8 and pyridine9 as donor groups. Ligands with nitrogen
donors have attracted the most attention; particularly, metal
complexes bearing pyridine-functionalized NHCs of Ir,10 Ag,11
Pd,12 Ru,13 and Ni14 have been synthesized. Those complexes
have shown catalytic activity in olefin polymerization reactions,15
CꢀC coupling reactions,16 transfer hydrogenation of ketones,17
hydrosilylation reactions,18 and reduction of nitroarenes.19
Among nitrogen donors, picoline has been used to generate
N-picolyl-NHC ligands which can be easily synthesized with
different substitution patterns on the picoline ring and the
NHC.20 This leads to a versatile ligand group for the study of
coordination properties.
Our group has broad experience with the stoichiometric
chemistry of pentamethylcyclopentadienyl ruthenium com-
plexes bearing P,P and P,N ligands.33,34 We aim to replace the
Ruthenium compounds with cyclopentadienyl type ligands
have been greatly studied because they are able to give rise to metas-
table 16-electron species with many potential catalytic applications.21
Nolan and co-workers have synthesized half-sandwich ruthenium
Received: July 22, 2011
Published: October 12, 2011
r
2011 American Chemical Society
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Organometallics
ARTICLE
phosphine fragment by an NHC, pursuing less toxic complexes
toward greener chemistry. Here we report a series of novel half-
sandwich ruthenium(II) picolyl-NHC complexes in which the
ligands have been varied systematically to study the influence of
the wingtip substituent as well as the substituents at the C-4 and
C-5 carbons of the imidazole ring on the steric and electronic
properties of the metal center. To obtain further information on
the donor strength of the carbene ligands, CO analogues were
synthesized and analyzed by infrared spectroscopy. The new
ruthenium compounds are active toward transfer hydrogenation
of a wide variety of ketones and imines under mild conditions
with almost quantitative conversions and short reaction times.
ligand precursors following literature procedures35ꢀ38 and, in
the case of 3-(phenyl)-1-(2-picolyl)imidazolium bromide and
3-(methyl)-1-(2-picolyl)-4,5-dichloroimidazolium bromide, by
reaction of the alkyl imidazolium and picolyl bromide in a
nonpolar solvent. The salts were isolated in high yields and
1
1
characterized by H and 13C{1H} NMR spectroscopy. The H
NMR spectra of c and f in DMSO-d6 showed a characteristic low-
field resonance for the C2 imidazolium proton at 10.95 and 10.81
ppm, respectively.
Synthesis of η5-Pentamethylcyclopentadienyl Picolyl-
NHC Ru(II) Complexes. The Ru(II) cationic complexes 1aꢀf
(Scheme 2) have been prepared as hexafluorophosphate salts
upon treatment of the metal precursor [(η5-C5Me5)Ru-
(CH3CN)3][PF6] with a THF solution of the appropriate ligand,
generated in situ by the reaction of the picolylimidazolium
bromide aꢀf and an excess of KtBuO. The reaction is complete
after 12 h at 65 °C. All products were purified by column
chromatography on Al2O3, with CH3CN as eluent, and isolated
in good yields. The new Ru(II) compounds were characterized
by 1H and 13C{1H} NMR and elemental analysis. All the
ruthenium picolyl-NHC complexes are very soluble in THF,
acetone, and chlorinated solvents but insoluble in nonpolar
solvents such as hexane, Et2O, and petroleum ether.
’ RESULTS AND DISCUSSION
Synthesis of Precursors of Picolyl-NHC Ligands. A series of
picolylimidazolium salts (aꢀf, Scheme 1) have been prepared as
1H NMR spectra of compounds 1aꢀf lack the C2 imidazolium
proton resonance signals at 10ꢀ12 ppm, indicating the coordi-
nation of the C2 carbene carbon to the metal center. Also, there
are two characteristic AB doublet signals at 5ꢀ6 ppm with
coupling constants of 14ꢀ15 Hz corresponding to the methylene
bridge protons, which become diastereotopic after coordination
of the ligands to the Ru atom, given the k2-C,N coordination.
Similar NMR features for (η5-C5Me5)Ru complexes with k2-P,N
chelating phosphinopicoline ligands have been observed.34b
Furthermore, this behavior has been reported by Xue and co-
workers in the synthesis of Ru(II) carbonyl Py-NHC
complexes.39 The 13C{1H} NMR signals of the carbene carbons
atoms of 1aꢀf (191ꢀ209 ppm) are located as expected for
(η5-C5Me5)Ru(NHC) compounds.22,23,32 It is interesting to note
the displacement to lower field, up to 209 ppm, of the NMR
resonance of the C2 carbon atom corresponding to the benzoi-
midazole analogue 1e. It is possible to explain this observation
due to destabilization in the imidazolium ring conjugation
produced by the attached benzene ring, which leads to a lower
electron density at the C2 carbon.
Figure 1. (a) [Ru(Cp-NHC)(CO)I]24 and (b) [(p-cymene)Ru-
(CabS.S)(3-methyl-1-picolylimidazolin-2-ylidene)].25
Scheme 1
Many attempts to crystallize compounds 1aꢀf were made in
different solvent combinations. However, it was not possible to
Scheme 2
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Organometallics
ARTICLE
Scheme 3
Figure 3. ORTEP view of the cationic complex in 3b, [Ru(η5-C5Me5)-
(NHC-k2C,N)(η2-O2)][B(ArF)4] (NHC
= 3-isopropyl-1-(2-pico-
lyl)imidazol-2-ylidene). Thermal ellipsoids are drawn at the 50%
probability level. Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Ru(1)ꢀcyclopentadienyl
(centroid) = 1.863(2), Ru(1)ꢀC(11) = 2.051(3), Ru(1)ꢀN(3) =
2.155(3), Ru(1)ꢀO(1) = 1.995(2), Ru(1)ꢀO(2) = 2.029(3), O(1)ꢀ
O(2) = 1.390(4), C(11)ꢀN(1) = 1.349(4), C(11)ꢀN(2) = 1.347(4);
O(1)ꢀRu(1)ꢀO(2) = 40.41(11), O(1)ꢀRu(1)ꢀC(11) = 115.81(12),
O(2)ꢀRu(1)ꢀC(11) = 85.68(12), O(1)ꢀRu(1)ꢀN(3) = 83.54(12),
O(2)ꢀRu(1)ꢀN(3) = 107.20(11), C(11)ꢀRu(1)ꢀN(3) = 84.33(12),
N(1)ꢀC(11)ꢀN(2) = 104.6(3).
X-ray diffraction were obtained after recrystallization on Et2O/
petroleum (1/2) (Scheme 3).
The η2-dioxygen complex 2b is stable in the solid state as well
as in solutions of Et2O and CH2Cl2. In previous work our group
reported dioxygen compounds containing the fragment {(η5-
C5Me5)Ru}, but in those cases the dissolution of the complexes
was unstable and led to transfer of dioxygen to the phosphino
ligand.40a However, oxygen transfer to the imidazolidene was not
observed, giving the possibility to explore in the future the
oxygen transfer capabilities of 2b to other substrates. The
stability of 2b is remarkable, as it is inverse to that of other
reported dioxygen complexes containing imidazolidene ligands
that easily undergo oxidation on the metal center.40b
Figure 2. ORTEP view of the cationic complex in 2a, [Ru(η5-C5Me5)-
(NHC-k2C,N)(NCCH3-k1N)][B(ArF)4] (NHC = 3-methyl-1-(2-pico-
lyl)imidazol-2-ylidene). Thermal ellipsoids are drawn at the 50%
probability level. Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Ru(1)ꢀcyclopentadienyl
(centroid) = 1.811(2), Ru(1)ꢀC(19) = 2.059(5), Ru(1)ꢀN(1) =
2.106(4), Ru(1)ꢀN(4) = 2.047(5), C(19)ꢀN(2) = 1.343(7), C-
(19)ꢀN(3) = 1.356(7); N(4)ꢀC(11) = 1.128(7); C(19)ꢀRu(1)ꢀN-
(1) = 84.3(2), C(19)ꢀRu(1)ꢀN(4) = 86.9(2), N(1)ꢀRu(1)ꢀN(4) =
91.8(2), N(2)ꢀC(19)ꢀN(3) = 105.3(5); N(4)ꢀC(11)ꢀC(12) =
172.4(8).
Complexes 2a,b were unambiguously characterized by X-ray
diffraction studies (Figures 2 and 3).
Both complexes adopt a piano stool geometry about the
ruthenium center, with the corresponding chelating NHC and
acetonitrile (2a) or η2-dioxygen ligands (2b). The RuꢀCcarbene
bonds, 2.059(5) Å in 2a and 2.051(3) Å in 2b, are slightly larger
than that of the complex [Ru(η5-C5Me5)(CꢀNH2)(py)]PF6,
2.03(1) Å,32 the only previously reported structure of a (η5-
C5Me5)Ru cationic complex containing a chelating NHC ligand,
but it is in the expected range of other Ru(η5-C5Me5)(NHC)L2
complexes.6a,23b,24 The RuꢀNpyridyl lengths found in 2a,b,
2.106(4) and 2.155(3) Å, respectively, are also comparable to
the 2.156(8) Å found for Ru(η5-C5Me5)(CꢀNH2)(py)]PF6.32
The acetonitrile ligand in 2a bonds linearly with characteristics
similar to those found for other Ru(η5-C5Me5) acetonitrile com-
plexes such as [(η5-C5Me5)Ru(MeCN)(k2-3-Ph2P-2-Me2N-
indene)][SO3CF3]41a and [Ru(η5-C5Me5)(MeCN)(MeTpm)]-
obtain crystals suitable for X-ray diffraction. Hence, an anion
exchange process of compounds 1a,b from PF6 to BAr4F (ArF =
3,5-bis(trifluoromethyl)phenyl) was completed. The anion ex-
change was accomplished quantitatively by stirring an ether
F
solution of 1a and NaBAr4 under argon for 24 h at room
temperature. The product 2a was then filtered through Celite to
remove NaPF6 to yield a brown-red solid. After recrystallization
on Et2O/petroleum (1/2) crystals that allowed us to unambigu-
ously determine the molecular structure of 2a by X-ray diffraction
were obtained. On the other hand, with complex 1b the anion
exchange process was completed in air, and after following an
experimental procedure similar to that previously mentioned the
η2-dioxygen complex 2b was obtained. Crystals of 2b suitable for
[PF6]
(
MeTpm
=
tris(3,5-dimethylpyrazolyl)methane).41b
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Organometallics
ARTICLE
Scheme 4
Scheme 5
Catalytic Transfer Hydrogenation. A few ruthenium NHC
complexes have been reported as catalysts for the transfer
hydrogenation of ketones.3b,45 Therefore, complexes 1a,b,e,f
were tested as catalysts for this transformation. The ruthenium
picolylcarbene complexes catalyze the transfer hydrogenation of
i
ketones and imines from PrOH with KOH as the initiator
(Scheme 5).
The reduction of acetophenone to 1-phenylethanol was used
as a representative reaction to screen the performance of Ru
picolylcarbene catalysts. The results given in Table 2 show the
influence of the wingtip and imidazole backbone substituents on
the catalytic activity. Catalysts containinga Me (entries 1, 5, and 6)
as a wingtip substituent are more active than those containing
isopropyl or mesityl (entries 3 and 4). This behavior indicates
that steric effects may be playing an important role in the catalytic
activity. However, it is important to note that the lower donor
character of the ligand with the chloro substituents on the
imidazole backbone in compound 1f (entry 6) shows a signifi-
cantly lower activity than its analogue 1a (entry 1) under the
same reaction conditions. Thus, electronic properties may also
account for the catalytic activity, although not as much as steric
effects. Compound 1a showed the best activity even with catalyst
Table 1. Selected IR Data (Nujol, cmꢀ1) for Compounds
3aꢀf and [(η5-C5Me5)Ru(CO)(iPr2PCH2Py)]BPh4
ν(CdO)
3a
1925
1920
1929
1928
1929
1937
1937
3b
3c
3d
3e
3f
[(η5-C5Me5)Ru(CO)(iPr2PCH2Py)]BPh4
44
Parameters for the dioxygen ligand in 2b indicate a η2-symme-
trical disposition. Also, the O1ꢀO2 bond distance is intermediate
between those of free dioxygen and peroxide ligand, as well as
close to those found in Ru(η5-C5Me5) complexes containing
bidentate phosphines such as [Ru(η5-C5Me5)(O2)(dippe)]-
[BPh4] (dippe = 1,2-bis(diisopropylphosphino)ethane),42a [Ru-
(η5-C5Me5)(O2)(dppm)][BPh4] (dppm = 1,1-bis(diphenylph-
osphino)methane),42b and [Ru(η5-C5Me5)(O2)(k2-P,N-iPr2-
PCH2Quin)][BAr04].42c
Synthesis of Carbonyl Derivatives. Several attempts have
been made to establish the donor properties of NHCs,43 and the
carbonyl derivatives of pentamethylcyclopentadienyl Ru(II)
complexes provide the opportunity to assess the basicity of
NHCs via infrared and NMR spectroscopy. The new carbonyl
complexes 3aꢀf can be easily synthesized by bubbling CO
through a DCM solution of the acetonitrile precursors 1aꢀf
(Scheme 4).
Infrared absorption energies corresponding to CO stretching
from compounds 3aꢀf provide valuable information regarding
the donor strength of the picolyl-NHC ligands (Table 1). The
difference in wingtip substituent does not significantly affect the
CO absorption energies. On the other hand, compound 3f
exhibits the highest stretching frequency, indicative of less
back-donation to CO from the metal center and a less electron
donating ligand set; this is consistent with the inclusion of Cl on
the NHC. It is interesting to note that compounds 3aꢀe show
significantly lower stretching frequencies on comparison with
those of 3f and the [(η5-C5Me5)Ru(CO)(iPr2PCH2Py)]BPh4
analogue; this experimental evidence reinforces the fact that
NHCs are stronger σ donors in comparison to phosphines. It is
necessary to modify the NHC backbone via the inclusion of a
chloride atom on the NHC, as observed for 3f, to diminish the
donating power of the ligand up to being comparable with
phosphines.
loadings as low as 0.1 mol %, giving a TOF up 100 minꢀ1
.
Catalyst 1a proved to be the most efficient of these complexes
in the transfer hydrogenation of acetophenone. Hence, several
aromatic and aliphatic ketones as well as imines were chosen
to explore the activity of 1a toward transfer hydrogena-
tions (Table 3). Aromatic halo substituents have an enhancing
effect on the catalytic activity, showing quantitative results on the
formation of the corresponding alcohols (entries 2 and 3).
However, MeO-substituted acetophenones showed lower yields
(entries 4ꢀ6), indicating a less efficient hydrogenation process.
Thus, electron-withdrawing groups on acetophenones benefit
the catalytic activity while electron donating groups decrease it.
On the other hand, benzophenone is quantitatively reduced to
1,1-diphenylmethanol (entry 7).
Complex 1a was demonstrated to be very active toward a
variety of alkyl ketones. Particularly, cyclohexanone was reduced
to cyclohexanol almost quantitatively (entry 8). Also 1a showed
activity for the synthesis of 2-(1-hydroxyethyl)cyclohexanol
(entry 9), which is an important building block in organic che-
mistry. However, the presence of two ketone groups diminishes
the reaction yields, even with an increased reaction time. Unsatu-
rated ketones are interesting substrates for TH reactions because
they may undergo reduction on the carbonyl and/or olefin
moiety. Nonetheless, 1a proved to selectively reduce the carbo-
nyl moiety on 6-methylhept-5-en-2-one (entry 10). Moreover,
2-acetylpyridine is efficiently hydrogenated (entry 11) almost
quantitatively with an increased reaction time of 3 h. Further-
more, complex 1a works as an efficient catalyst in the hydro-
genation of N-benzylideneaniline (entry 12), demonstrating
the versatility of the new catalyst toward the hydrogenation
of ketones and imines. Our catalyst system has exhibited much
better catalytic activity and works on a wider scope of sub-
strates than do previously reported ruthenium pyridyl-NHC
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Organometallics
ARTICLE
Table 2. Influence of Wingtips and Backbone Substituents on
Table 3. Catalytic Transfer Hydrogenation
the Catalytic Activity of Ru Picolylcarbene Complexesa
cat. R wingtip
group
cat. R1
TOF50
c
entry catalyst
backbone group t (min)b (minꢀ1
)
1
2
3
4
5
1a
1a
1b
1d
1e
Me
H
10
60
62
100d
16
Me
iPr
H
H
40
mesityl
Me
H
>1000
30
0.38
16
ꢀCHdCHꢀ
CHdCHꢀ
Cl
6
1f
Me
15
20
a Transfer hydrogenation of acetophenone reaction conditions: 2.00
mmol of acetophenone, KOH (10 mol %), catalyst (1 mol %) in 4 mL of
iPrOH. b Reaction time required for conversions >90%. c Turnover
frequency at 50% conversion. d 0.1 mol % of catalyst loading.
complexes.46 Furthermore, compound 1a has shown better
performance when compared with (C5Me5)Ir(NHC) com-
plexes, as evidenced in the lower reaction times and catalyst
loadings needed to complete the reactions.47 It is reasonable to
assume that catalytic transfer hydrogenation reaction of 1a
occurs via a monohydride mechanism, as has been reported for
other ruthenium Cp analogues.48
’ CONCLUSION
We have reported the synthesis and characterization of novel
[(η5-C5Me5)Ru(picolyl-NHC)(CH3CN)][PF6] (1aꢀf) com-
plexes in which the substituents on the NHC backbone and
wingtip have been modified. The crystal structures of two of the
complexes prepared (2a,b) after completing an anion exchange
process have been described. The reactivity of such complexes
toward CO led to the production of carbonyl derivatives 3aꢀf.
An infrared spectroscopy study of the CO stretching frequencies
of carbonyl complexes 3aꢀf has shown that picolyl-NHC ligands
aꢀd are stronger donors than the analogous picolyl-phosphine
ligand. Furthermore, the inclusion of chloride on the NHC
backbone is needed to obtain a less donating ligand (f) compar-
able to phosphines.
The catalytic study of [(η5-C5Me5)Ru(picolyl-NHC)(CH3CN)]
[PF6] complexes 1aꢀf toward transfer hydrogenation reactions of
acetophenone was completed, showing high activity in most cases.
The results also showed that picolylcarbenes are tunable ligands that
with small changes can lead to an increase of catalytic activity.
Particularly, complex 1a has proved to be a versatile and efficient
transfer hydrogenation catalyst with outstanding activity in compar-
ison to its analogues and other ruthenium and iridium complexes.46,47
Furthermore, 1a has shown high tolerance to functional groups on
the reduction of a wide range of ketones and imines.
a Transfer hydrogenation reaction conditions: 2.00 mmol of substrate,
i
KOH (10 mol %), catalyst (0.1 mol %) in 4 mL of PrOH at 82 °C.
c Product yield determined by GC-MS using 1,3,5-trimethoxybenzene
as an internal standard. Turnover number (TON) = (mmol of pro-
duct)/(mmol of catalyst) after time t.
3-methyl-1-(2-picolyl)benzoimidazolium bromide (e),38 [(η5-C5Me5)-
Ru(CH3CN)3][PF6],49 and NaBArF 50 were prepared using slightly
4
’ EXPERIMENTAL SECTION
modified versions of the published procedures. All other reagents
were purchased from commercial sources and used without further
purification.
General Methods. Unless otherwise stated, all manipulations were
carried out under dry nitrogen or argon using conventional Schlenk
techniques. Tetrahydrofuran, diethyl ether, and petroleum ether
(boiling range 40ꢀ60 °C) were obtained free of oxygen and water with
an Innovative Technology Inc. solvent purification system. Acetonitrile
and dichloromethane were of anhydrous quality and used as received. All
solvents were degassed immediately prior to use. 3-Methyl-1-(2-pico-
lyl)imidazolium bromide (a),35 3-isopropyl-1-(2-picolyl)imidazolium
bromide (b),36 3-mesityl-1-(2-picolyl)imidazolium bromide (d),37
NMR spectra were recorded using Varian INOVA 400 MHz
and Varian Inova 600 MHz spectrometers, and chemical shifts are
1
reported relative to TMS for H and 13C{1H} and 85% H3PO4 for
31P{1H}. Assignments of 1H and 13C{1H} NMR spectra were made on
the basis of 2D NMR experiments. IR spectra were recorded in Nujol
mulls with a Perkin-Elmer FTIR Spectrum 1000 spectrophotometer.
Microanalyses were performed with a LECO CHNS-932 elemental
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analyzer by Servicios Centrales de Ciencia y Tecnología, Universidad de
Cꢀadiz. GC-MS analyses were recorded in an Agilent 6890N device.
3-Phenyl-1-(2-picolyl)imidazolium Bromide (c). 2-(Bromo-
methyl)pyridine hydrobromide (1.01 g, 4 mmol) was neutralized using a
saturated aqueous solution of Na2CO3. The released 2-(bromo-
methyl)pyridine was extracted using ice-cold diethyl ether (3 ꢁ
30 mL). The solution was dried with Na2SO4 and filtered into a
dissolution of 1-phenylimidazole (0.58 g, 4 mmol) in 1,4-dioxane
(30 mL). Diethyl ether was removed under reduced pressure and the
reaction mixture refluxed for 12 h. The volatiles were removed under
reduced pressure, and the oily residue was purified by repetitive
precipitation from CH2Cl2/Et2O. The resulting light brown solid was
100 MHz, SiMe4): δ 193.28 (CimidRu), 158.61 (Cpy), 157.79 (Cpy),
138.00 (Cpy), 125.25 (Cpy), 125.14 (Cpy), 122.70 (Cimid), 122.56 (Cimid),
83.10 (C5-(CH3)5), 55.07 (CH2), 36.97(NCH3), 10.31 (C5(CH3)5), 3.57
(CH3). IR (Nujol, cmꢀ1): ν 1590, 1458, 1402, 1377, 1301, 1246, 1222,
1180, 1107, 1075, 1027, 947, 843, 762, 724, 687. Anal. Calcd for
C22H29F6N4PRu: C, 44.37; H, 4.91; N, 9.41. Found: C, 44.35; H, 4.94;
N, 9.38.
Acetonitrile(η5-pentamethylcyclopentadienyl)(k2-C,N-3-isopropyl-
1-(2-picolyl)imidazol-2-ylidene)ruthenium(II) Hexafluorophosphate
(1b). The reaction was carried out with 3-isopropyl-1-(2-pico-
lyl)imidazolium bromide (b; 0.30 g, 1.1 mmol) and potassium tert-
butoxide (0.35 g, 3.2 mmol) in THF (30 mL) followed by the addition of
[(η5-C5Me5)Ru(CH3CN)3][PF6] (0.45 g, 0.9 mmol). The product was
a reddish microcrystalline solid. Yield: 0.41 g, 73%. 1H NMR (acetone-
d6, 400 MHz, SiMe4): δ 8.98 (d, 3JHH = 5.27 Hz, 1H, Hpy), 7.88 (t, 1H,
1
dried in vacuo. Yield: 0.76 g, 60%. H NMR (DMSO-d6, 400 MHz,
SiMe4): δ 10.95 (s, 1H, NCHN), 8.45 (d, 3JHH = 4.69 Hz, 1H, Hpy), 7.85
(s, 1H, Himid backbone), 7.82 (d, 1H, 3JHH = 7.97 Hz, 1H, Hpy), 7.78 (s,
1H, Himid backbone), 7.68 (m, 2H, HPh), 7.65 (t, 3JHH = 7.76 Hz, 1H, Hpy),
7.46 (m, 3H, HPh), 7.21 (m, 1H, Hpy), 5.92 (s, 2H, Hbridge). 13C{1H}
NMR (CDCl3, 100 MHz, SiMe4): δ 152.25 (Cpy), 149.64 (Cpy), 137.50
(Cpy), 135.76 (Cimid), 134.27 (CPh), 130.42 (CPh), 130.09 (Cpy), 124.11
(Cpy), 123.88 (Cimid), 123.7289 (Cimid),, 121.62 (CPh), 120.28 (CPh),
53.91 (CH2). Anal. Calcd for C15H14BrN3: C, 56.98; H, 4.46; N, 13.29.
Found: C, 56.95; H, 4.41; N, 13.33.
3
3JHH3 = 7.62 Hz, 1H, Hpy), 7.65 (d, JHH = 7.61 Hz, 1H, Hpy), 7.51
3
(d, JHH = 2.05 Hz, 1H, Himid backbone), 7.42 (d, JHH = 1.76 Hz, 1H,
Himid backbone), 7.40 (t, 3JHH = 7.03 Hz, 1H, Hpy), 5.48 (d, 2JHH = 14.94
Hz, 1H, Hbridge), 5.07 (m, 3JHH = 6.74 Hz, 1H, NCH(CH3)2), 4.81 (d,
2JHH = 14.64 Hz, 1H, Hbridge), 2.48 (s, 3H, CH3), 1.64 (d, 3JHH = 6.74
Hz, 3H, NCH(CH3)2), 1.59 (s, 15H, (C5-(CH3)5), 1.38 (d, 3JHH = 6.74
Hz, 3H, NCH(CH3)2). 13C{1H} NMR (acetone-d6, 100 MHz, SiMe4):
δ 191.42 (CimidRu), 158.45 (Cpy), 157.44 (Cpy), 137.76 (Cpy), 124.97
(Cpy), 124.93 (Cimid), 122.96 (Cimid), 117.46 (Cpy), 95.64 (NCCH3),
82.85 (C5(CH3)5), 54.77 (CH2), 51.52 (NCH(CH3)2), 24.70
(NCH(CH3)2), 23.46 (NCH(CH3)2), 10.09 (C5(CH3)5), 3.54
(NCCH3). IR (Nujol, cmꢀ1): ν 1732, 1644, 1602, 1590, 1566, 937.
Anal. Calcd for C24H33F6N4PRu: C, 46.23; H, 5.33; N, 8.98. Found: C,
46.19; H, 5.36; N, 8.96.
3-Methyl-1-(2-picolyl)-4,5-dichloroimidazolium Bromide
(f). 2-(Bromomethyl)pyridine hydrobromide (1.01 g, 4 mmol) was
neutralized using a saturated aqueous solution of Na2CO3. The liberated
2-(bromomethyl)pyridine was extracted using ice-cold diethyl ether
(3 ꢁ 30 mL). The solution was dried with Na2SO4 and filtered into a
dissolution of 1-methyl-4,5-dichloroimidazole (0.60 g, 4 mmol) in
CH3CN (30 mL). Diethyl ether was removed under reduced pressure
and the reaction mixture refluxed for 3 days. The reaction mixture
was filtered, and the solvent was evaporated under reduced pressure.
The resulting yellow solid was washed with Et2O (3 ꢁ 10 mL) and dried
in vacuo. Yield: 0.52 g, 40%. 1H NMR (DMSO-d6, 400 MHz, SiMe4):
δ 10.81 (s, 1H, NCHN), 8.33 (d, 3JHH = 4.10 Hz, 1H, Hpy), 7.63 (t, 1H,
3JHH = 7.62 Hz, 1H, Hpy), 7.48 (d, 3JHH = 7.61 Hz, 1H, Hpy), 7.14 (t,
3JHH = 4.10 Hz, 1H, Hpy), 5.71 (s, 2H, CH2), 3.94 (s, 3H, NCH3).
13C{1H} NMR (DMSO-d6, 100 MHz, SiMe4): δ 150.68 (Cpy), 149.48
(Cpy), 138.42 (Cimid), 137.90 (Cpy), 124.01 (Cpy), 123.02 (Cpy), 119.92
(Cimid), 119.57 (Cimid), 52.56 (CH2), 35.57 (NCH3). Anal. Calcd for
C10H10BrCl2N3: C, 37.18; H, 3.12; N, 13.01. Found: C, 37.16; H, 3.08;
N, 13.02.
Acetonitrile(η5-pentamethylcyclopentadienyl)(k2-C,N-3-phenyl-
1-(2-picolyl)imidazol-2-ylidene)ruthenium(II) Hexafluorophosphate
(1c). The reaction was carried out with 3-phenyl-1-(2-picolyl)imidazo-
lium bromide (c; 0.35 g, 1.1 mmol) and potassium tert-butoxide (0.35 g,
3.2 mmol) in THF (30 mL) followed by the addition of [(η5-
C5Me5)Ru(CH3CN)3][PF6] (0.50 g, 1 mmol). The product was a
reddish microcrystalline solid. Yield: 0.44 g, 67%. 1H NMR (acetone-d6,
400 MHz, SiMe4): δ 8.98 (d, 3JHH = 5.58 Hz, 1H, Hpy), 7.93 (t, 1H, 3JHH
7.62 Hz, 1H, Hpy), 7.70 (d, 3JHH = 7.71 Hz, 1H, Hpy), 7.69 (d, 3JHH
=
=
1.96 Hz, 1H, Himid backbone), 7.68 (d, 3JHH = 8.84 Hz, 2H, HPh), 7.61 (t,
3JHH = 7.86 Hz, 2H, HPh), 7.50 (m, 1H, HPh), 7.51 (d, 3JHH = 1.96 Hz,
1H, Himid backbone), 7.44 (t, 3JHH = 6.44 Hz, 1H, Hpy), 5.61 (d, 2JHH
=
14.88 Hz, 1H, Hbridge), 4.94 (d, 2JHH = 14.69 Hz, 1H, Hbridge), 2.50 (s,
3H, CH3), 1.35 (s, 15H, (C5(CH3)5). 13C{1H} NMR (acetone-d6, 100
MHz, SiMe4): δ 193.62 (CimidRu), 158.20 (Cpy), 157.28 (Cpy), 141.57
(NCPh), 137.91 (Cpy), 129.44 (CPh), 128.74 (CPh), 127.38 (CPh),
125.20 (Cpy), 125.03 (Cpy), 123.80 (Cimid), 123.21 (Cimid), 83.21
(C5(CH3)5), 55.49 (CH2), 9.91 (C5(CH3)5), 4.91 (NCCH3). Anal.
Calcd for C27H31F6N4PRu: C, 49.31; H, 4.75; N, 8.52. Found: C, 49.27;
H, 4.74; N, 8.55.
Representative Procedure for the Synthesis of Metal
Complexes (1aꢀf). A suspension of the appropriate picolylimidazo-
lium bromide (aꢀf) and potassium tert-butoxide in THF was stirred at
room temperature for 5 h. [(η5-C5Me5)Ru(CH3CN)3][PF6] was added
to the mixture and stirred under reflux for 12 h. The suspension was
filtered through a pad of Na2SO4 to remove the bromide salt and the
solvent evaporated under reduced pressure. The resulting solid was
dissolved in acetonitrile and eluted through a neutral Al2O3 column with
CH3CN as a solvent. The solvent was removed under reduced pressure
and the solid washed with petroleum ether and dried under vacuum.
Acetonitrile(η5-pentamethylcyclopentadienyl)(k2-C,N-3-methyl-
1-(2-picolyl)imidazol-2-ylidene)ruthenium(II) Hexafluorophosphate
(1a). The reaction was carried out with 3-methyl-1-(2-picolyl)imidazo-
lium bromide (a; 0.25 g, 1 mmol) and potassium tert-butoxide (0.33 g, 3
mmol) in THF (30 mL) followed by the addition of [(η5-C5Me5)Ru-
(CH3CN)3][PF6] (0.40 g, 0.8 mmol). The product was a yellowish
Acetonitrile(η5-pentamethylcyclopentadienyl)(k2-C,N-3-mesityl-
1-(2-picolyl)imidazol-2-ylidene)ruthenium(II) Hexafluorophosphate
(1d). The reaction was carried out with 3-mesityl-1-(2-picolyl)imida-
zolium bromide (d; 0.39 g, 1.1 mmol) and potassium tert-butoxide (0.35
g, 3.2 mmol) in THF (30 mL) followed by the addition of [(η5-
C5Me5)Ru(CH3CN)3][PF6] (0.50 g, 1 mmol). The product was a
reddish microcrystalline solid. Yield: 0.58 g, 84%. 1H NMR (acetone-d6,
3
400 MHz, SiMe4): δ 8.91 (d, JHH = 5.57 Hz, 1H, Hpy), 7.91 (t, 1H,
3JHH = 7.62 Hz, 1H, Hpy), 7.75 (d, 3JHH = 8.19 Hz, 1H, Hpy), 7.74 (d,
3JHH = 2.05 Hz, 1H, Himid backbone), 7.38 (t, 3JHH = 7.03 Hz, 1H, Hpy),
7.13 (d, 3JHH = 2.05 Hz, 1H, Himid backbone), 7.09 (s, 1H, Hmes), 7.01 (s,
1H, Hmes), 5.65 (d, 2JHH = 14.94 Hz, 1H, Hbridge), 4.87 (d, 2JHH = 14.64
Hz, 1H, Hbridge), 2.35 (s, 3H, CH3), 2.33 (s, 3H, CH3), 2.08 (s, 3H,
CH3), 1.51 (s, 3H, CH3), 1.41 (s, 15H, (C5(CH3)5). 13C{1H} NMR
(acetone-d6, 100 MHz, SiMe4): δ 193.25 (CimidRu), 158.97 (Cpy),
1
microcrystalline solid. Yield: 0.31 g, 66%. H NMR (acetone-d6, 400
MHz, SiMe4): δ 8.97 (d, 3JHH = 5.57 Hz, 1H, Hpy), 7.89 (t, 1H, 3JHH
=
=
7.62 Hz, 1H, Hpy), 7.64 (d, 3JHH = 7.62 Hz, 1H, Hpy), 7.47 (d, 3JHH
3
1.76 Hz, 1H, Himid backbone), 7.39 (t, JHH = 6.41 Hz, 1H, Hpy), 7.31
(d, 3JHH = 1.76 Hz, 1H, Himid backbone), 5.58 (d, 2JHH = 15.23 Hz, 1H,
2
Hbridge), 4.75 (d, JHH = 15.23 Hz, 1H, Hbridge), 3.92 (s, 3H, NCH3),
2.45 (s, 3H, CH3), 1.61 (s, 15H, (C5(CH3)5). 13C{1H} NMR(acetone-d6,
5798
dx.doi.org/10.1021/om200665f |Organometallics 2011, 30, 5793–5802

Organometallics
ARTICLE
157.18 (Cpy), 139.27 (NCmes), 138.01 (Cpy), 137.70 (Cmes), 137.29
(Cmes), 135.75 (Cmes), 129.27 (Cmes), 128.69 (Cmes), 125.41 (Cpy),
124.99 (Cpy), 124.27 (Cimid), 123.40 (Cimid), 83.10 (C5(CH3)5), 56.08
(CH2), 21.01 (CH3), 19.17 (CH3), 18.04 (CH3), 10.15 (C5(CH3)5),
4.44 (NCCH3). IR (Nujol, cmꢀ1): ν 2258, 2177, 1592, 1452, 1371,
1021, 837. Anal. Calcd for C30H37F6N4PRu: C, 51.50; H, 5.33; N, 8.01.
Found: C, 51.54; H, 5.29; N, 7.98.
NCH(CH3)2), 1.44 (s, 15H, (C5(CH3)5), 13C{1H} NMR (CD2Cl2,
100 MHz, SiMe4): δ 180.22 (CimidRu), 162.11 (q, 1JBꢀC = 49.72 Hz,
B(C6H3C2F6)4), 154.42 (Cpy), 152.51 (Cpy), 140.31 (Cpy), 135.17
(B(C6H3C2F6)4), 129.26 (q, 2JCꢀF = 31.60 Hz, B(C6H3C2F6)4), 125.87
(Cpy), 125.83 (Cimid), 124.96 (q, 1JCꢀF = 272.24 Hz, B(C6H3C2F6)4),
124.24 (Cpy), 121.16 (Cimid), 104.15 (C5(CH3)5), 54.39 (CH2), 53.29
(NCH(CH3)2), 26.08 (NCH(CH3)2), 24.10 (NCH(CH3)2), 9.16
(C5(CH3)5). Anal. Calcd for C54H42BF24N3O2Ru: C, 48.66; H, 3.18;
N, 3.15. Found: C, 48.63; H, 3.22; N, 3.21.
Acetonitrile(η5-pentamethylcyclopentadienyl)(k2-C,N-3-methyl-
1-(2-picolyl)benzoimidazol-2-ylidene)ruthenium(II) Hexafluoropho-
sphate (1e). The reaction was carried out with 3-methyl-1-(2-pico-
lyl)benzoimidazolium bromide (e; 0.33 g, 1.1 mmol) and potassium tert-
butoxide (0.35 g, 3.2 mmol) in THF (30 mL) followed by the addition of
[(η5-C5Me5)Ru(CH3CN)3][PF6] (0.50 g, 1 mmol). The product was a
Representative Procedure for the Synthesis of Carbonyl
Metal Complexes (3aꢀf). A solution of the metal complex 1aꢀf in
CH2Cl2 was stirred under CO (1 atm) for 2 h. The solvent was removed
under reduced pressure; the resulting solid was washed with petroleum
ether and dried under vacuum.
1
yellowish orange microcrystalline solid. Yield: 0.49 g, 75%. H NMR
Carbonyl(η5-pentamethylcyclopentadienyl)(k2-C,N-3-methyl-
1-(2-picolyl)imidazol-2-ylidene)ruthenium(II) Hexafluorophosphate
(3a). The reaction was carried out with 1a (60 mg, 0.1 mmol). The
3
(acetone-d6, 400 MHz, SiMe4): δ 8.95 (d, JHH = 5.60 Hz, 1H, Hpy),
7.89 (t, 1H, 3JHH = 7.60 Hz, 1H, Hpy), 7.82 (d, 3JHH = 7.60 Hz, 1H, Hpy),
7.74 (m, 1H, Hbenzimid), 7.51 (m, 1H, Hbenzimid), 7.41 (t, 3JHH = 6.44 Hz,
1
2
product was a brownish microcrystalline solid. Yield: 55 mg, 97%. H
1H, Hpy), 7.27 (m, 2H, Hbenzimid), 5.94 (d, JHH = 15.23 Hz, 1H,
NMR (CDCl3, 400 MHz, SiMe4): δ 8.52 (d, 3JHH = 5.85 Hz, 1H, Hpy),
7.77 (t, 1H, 3JHH = 7.62 Hz, 1H, Hpy), 7.72 (d, 3JHH = 7.03 Hz, 1H, Hpy),
7.42 (d, 3JHH = 2.05 Hz, 1H, Himid backbone), 7.17 (t, 3JHH = 6.44 Hz, 1H,
Hpy), 7.00 (d, 3JHH = 2.05 Hz, 1H, Himid backbone), 5.52 (d, 2JHH = 15.82
2
Hbridge), 4.92 (d, JHH = 15.23 Hz, 1H, Hbridge), 4.13 (s, 3H, NCH3),
2.42 (s, 3H, CH3), 1.63 (s, 15H, (C5(CH3)5). 13C{1H} NMR (acetone-
d6, 100 MHz, SiMe4): δ 208.65 (CimidRu), 158.27 (Cpy), 157.74 (Cpy),
138.28 (Cpy), 136.57 (Cbenzimid), 135.62 (Cbenzimid), 125.46 (Cpy),
125.43 (Cpy), 123.09 (Cbenzimid), 122.98 (Cbenzimid), 110.40 (Cbenzimid),
109.78 (Cbenzimid), 84.27 (C5(CH3)5), 68.00 (NC), 51.20 (CH2),
34.23 (NCH3), 10.28 (C5(CH3)5), 3.60 (NCCH3). IR (Nujol, cmꢀ1):
ν 2256, 2199, 2062, 1951, 1593, 1451, 1368. Anal. Calcd for C26H31-
F6N4PRu: C, 48.37; H, 4.84; N, 8.68. Found: C, 48.40; H, 4.86; N, 8.71.
Acetonitrile(η5-pentamethylcyclopentadienyl)(k2-C,N-3-methyl-
1-(2-picolyl)-4,5-dichloroimidazol-2-ylidene)ruthenium(II) Hexafluor-
ophosphate (1f). The reaction was carried out with 3-methyl-1-(2-
picolyl)-4,5-dichloroimidazolium bromide (f; 0.36 g, 1.1 mmol) and
potassium tert-butoxide (0.35 g, 3.2 mmol) in THF (30 mL) followed by
the addition of [(η5-C5Me5)Ru(CH3CN)3][PF6] (0.50 g, 1 mmol).
The product was a yellowish microcrystalline solid. Yield: 0.51 g, 77%.
1H NMR (acetone-d6, 400 MHz, SiMe4): δ 8.98 (d, 3JHH = 5.13 Hz, 1H,
Hpy), 7.94 (t, 1H, 3JHH = 7.62 Hz, 1H, Hpy), 7.79 (d, 3JHH = 7.61 Hz, 1H,
Hpy), 7.45 (t, 3JHH = 6.52 Hz, 1H, Hpy), 5.58 (d, 2JHH = 15.23 Hz, 1H,
2
Hz, 1H, Hbridge), 4.51 (d, JHH = 15.82 Hz, 1H, Hbridge), 3.68 (s, 3H,
NCH3), 1.61 (s, 15H, (C5(CH3)5). 13C{1H} NMR (CDCl3, 100 MHz,
SiMe4): δ 203.86 (CO), 178.93 (CimidRu), 158.44 (Cpy), 156.51 (Cpy),
139.54 (Cpy), 127.02 (Cpy), 124.72 (Cpy), 123.65 (Cimid), 122.99
(Cimid), 94.78 (C5(CH3)5), 54.19 (CH2), 37.21 (NCH3), 10.18
(C5(CH3)5). IR (Nujol, cmꢀ1): ν 1925 (CO). Anal. Calcd for
C21H26F6N3OPRu: C, 43.30; H, 4.50; N, 7.21. Found: C, 43.32; H,
4.47; N, 7.17.
Carbonyl(η5-pentamethylcyclopentadienyl)(k2-C,N-3-isopropyl-
1-(2-picolyl)imidazol-2-ylidene)ruthenium(II) Hexafluorophosphate
(3b). The reaction was carried out with 1b (63 mg, 0.1 mmol). The
1
product was a brownish microcrystalline solid. Yield: 61 mg, 99%. H
NMR (acetone-d6, 400 MHz, SiMe4): δ 8.90 (d, 3JHH = 5.54 Hz, 1H, Hpy),
8.07 (t, 1H, 3JHH = 7.66 Hz, 1H, Hpy), 7.83 (d, 3JHH = 7.66 Hz, 1H, Hpy),
7.68 (d, 3JHH = 2.12 Hz, 1H, Himid backbone), 7.58 (d, 3JHH = 1.85 Hz, 1H,
Himid backbone), 7.47 (t, 3JHH = 6.61 Hz, 1H, Hpy), 5.69 (d, 2JHH = 15.58
2
Hbridge), 4.75 (d, JHH = 15.23 Hz, 1H, Hbridge), 3.97 (s, 3H, NCH3),
Hz, 1H, Hbridge), 4.82 (d, 2JHH = 15.58 Hz, 1H, Hbridge) 4.75 (m, 3JHH
6.74 Hz, 1H, NCH(CH3)2), 1.77 (s, 15H, (C5(CH3)5), 1.60 (d, 3JHH
=
=
2.45 (s, 3H, CH3), 1.63 (s, 15H, (C5(CH3)5). 13C{1H} NMR (acetone-
d6, 100 MHz, SiMe4): δ 196.52 (CimidRu), 157.61 (Cpy), 156.91 (Cpy),
138.21 (Cpy), 125.46 (Cpy), 124.88 (Cpy), 116.60 (Cimid), 115.65
(Cimid), 83.65 (C5(CH3)5), 52.45 (CH2), 35.71 (NCH3), 9.96
(C5(CH3)5), 3.38 (NCCH3). IR (Nujol, cmꢀ1): ν 2255, 2188, 2079,
2044, 1944, 1594, 1456, 1376, 722. Anal. Calcd for C22H27Cl2F6N4PRu:
C, 39.77; H, 4.10; N, 8.43. Found: C, 39.79; H, 4.06; N, 8.40.
Procedure for Anion Exchange Reactions (2a,b). A suspen-
sion of the appropriate metal complex 1a,b and 1 equiv of NaBAr4F in
ether was stirred at room temperature for 24 h. The suspension was
filtered through a pad of Celite and the solvent evaporated under
reduced pressure. The resulting solid was washed with petroleum ether
and dried under vacuum.
6.87 Hz, 3H, NCH(CH3)2), 1.41 (d, 3JHH = 6.60 Hz, 3H, NCH(CH3)2).
13C{1H} NMR (acetone-d6, 100 MHz, SiMe4): δ 205.06 (CO), 177.96
(CimidRu), 159.88 (Cpy), 157.34 (Cpy), 140.31 (Cpy), 127.15 (Cpy),
125.72 (Cpy), 124.55 (Cimid), 119.07 (Cimid), 95.58 (C5(CH3)5), 54.61
(CH2), 52.54 (NCH(CH3)2), 24.07 (NCH(CH3)2), 23.23 (NCH-
(CH3)2), 9.87 (C5(CH3)5). IR (Nujol, cmꢀ1): ν 1920 (CO). Anal. Calcd
for C23H30F6N3OPRu: C, 45.25; H, 4.95; N, 6.88. Found: C, 45.21; H,
4.92; N, 6.91.
Carbonyl(η5-pentamethylcyclopentadienyl)(k2-C,N-3-phenyl-
1-(2-picolyl)imidazol-2-ylidene)ruthenium(II) Hexafluorophosphate
(3c). The reaction was carried out with 1c (66 mg, 0.1 mmol). The
1
(η2-O2)(η5-pentamethylcyclopentadienyl)(k2-C,N-3-isopropyl-
1-(2-picolyl)imidazol-2-ylidene)ruthenium(II) BAr4F (2b). A suspension
of 1b (0.19 g, 0.3 mmol) and NaBAr4F (0.26 g, 0.3 mmol) was stirred in
air at room temperature for 24 h. The suspension was filtered through a
pad of Celite and the solvent evaporated under reduced pressure. The
product was obtained as a brown microcrystalline solid. Yield: 0.29 g,
73%. 1H NMR (CD2Cl2, 400 MHz, SiMe4): δ 9.22 (d, 3JHH = 5.85 Hz,
product was a brownish microcrystalline solid. Yield: 62 mg, 95%. H
NMR (acetone-d6, 400 MHz, SiMe4): δ 8.89 (d, 3JHH = 5.62 Hz, 1H,
Hpy), 8.11 (t, 1H, 3JHH = 7.69 Hz, 1H, Hpy), 7.88 (d, 3JHH = 7.10 Hz, 1H,
Hpy), 7.82 (d, 3JHH = 1.97 Hz, 1H, Himid backbone), 7.60 (d, 3JHH = 4.34
3
Hz, 2H, HPh), 7.57 (m, 3H, HPh), 7.55 (d, JHH = 1.78 Hz, 1H,
3
2
Himid backbone), 7.50 (t, JHH = 6.30 Hz, 1H, Hpy), 5.82 (d, JHH
=
15.57 Hz, 1H, Hbridge), 4.99 (d, 2JHH = 15.58 Hz, 1H, Hbridge), 1.56 (s,
15H, (C5(CH3)5). 13C{1H} NMR (acetone-d6, 100 MHz, SiMe4): δ
206.27 (CO), 180.01 (CimidRu), 160.08 (Cpy), 159.98 (CPh), 157.39
(Cpy), 140.60 (Cpy), 129.75 (CPh), 128.38 (CPh), 127.2 (Cpy), 125.99
(Cimid), 124.26 (Cimid), 95.43 (C5(CH3)5), 55.32 (CH2), 9.79 (C5(CH3)5.
IR (Nujol, cmꢀ1): ν 1929 (CO). Anal. Calcd for C26H28F6N3OPRu: C,
48.45; H, 4.38; N, 6.52. Found: C, 48.44; H, 4.35; N, 6.54.
3
1H, Hpy), 7.85 (t, 1H, JHH = 7.62 Hz, 1H, Hpy), 7.72 (br s, 8H,
B(C6H3C2F6)4), 7.56 (br s, 4H, B(C6H3C2F6)4), 7.49 (t, 3JHH = 6.45
3
Hz, 1H, Hpy), 7.45 (d, JHH = 7.62 Hz, 1H, Hpy), 7.32 (m, 2H,
Himid backbone), 5.15 (d, 2JHH = 15.82 Hz, 1H, Hbridge), 4.73 (m, 3JHH
=
6.66 Hz, 1H, NCH(CH3)2), 4.41 (d, 2JHH = 15.82 Hz, 1H, Hbridge), 1.70
3
3
(d, JHH = 6.45 Hz, 3H, NCH(CH3)2), 1.60 (d, JHH = 7.03 Hz, 3H,
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dx.doi.org/10.1021/om200665f |Organometallics 2011, 30, 5793–5802

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Table 4. Summary of Crystallographic Data for 2a,b
Carbonyl(η5-pentamethylcyclopentadienyl)(k2-C,N-3-methyl-1-
(2-picolyl)benzoimidazol-2-ylidene)ruthenium(II) Hexafluoropho-
sphate (3e). The reaction was carried out with 1e (65 mg, 0.1 mmol).
The product was a brownish microcrystalline solid. Yield: 62 mg,
99%. 1H NMR (acetone-d6, 400 MHz, SiMe4): δ 8.95 (d, 3JHH = 5.57
2a
2b
formula
C54H41BF24
-
C56.32H47.53
N4Ru
BCl1.12
-
Hz, 1H, Hpy), 8.12 (t, 1H, 3JHH = 7.61 Hz, 1H, Hpy), 8.04 (d, 3JHH
=
F24N3O2.44Ru
1412.93
7.91 Hz, 1H, Hpy), 7.91 (m, 1H, Hbenzimid), 7.69 (m, 1H, Hbenzimid),
fw
1313.79
100
3
7.51 (t, JHH = 6.15 Hz, 1H, Hpy), 7.41 (m, 2H, Hbenzimid), 6.19 (d,
2JHH = 15.81 Hz, 1H, Hbridge), 5.00 (d, 2JHH = 15.81 Hz, 1H, Hbridge),
4.13 (s, 3H, NCH3), 1.85 (s, 15H, (C5(CH3)5). 13C{1H} NMR
T (K)
100
cryst size (mm)
0.53 ꢁ 0.36 ꢁ
0.11
(acetone-d6, 100 MHz, SiMe4):
δ 204.61 (CO), 194.70
(CbenzimidRu), 160.24 (Cpy), 157.41 (Cpy), 140. 75 (Cpy), 136.39
(NCbenzimid), 135.48 (NCbenzimid), 127.60 (Cpy), 126.21 (Cpy),
124.28 (Cbenzimid), 124.12 (Cbenzimid), 111.59 (Cbenzimid), 110.89
(Cbenzimid), 96.29 (C5(CH3)5), 51.44 (CH2), 34.95 (NCH3), 10.18
(C5(CH3)5), 4.91 (NCCH3). IR (Nujol, cmꢀ1): ν 1929 (CO). Anal.
Calcd for C25H28F6N3OPRu: C, 47.47; H, 4.46; N, 6.64. Found: C,
47.45; H, 4.49; N, 6.67.
cryst syst
Space group
cell params
a (Å)
triclinic
monoclinic
P21/c
P1
12.427(3)
12.814(3)
17.884(4)
91.85(3)
100.30(3)
104.44(3)
2704.5(9)
2
12.498(3)
17.896(4)
26.458(5)
90.00
b (Å)
c (Å)
Carbonyl(η5-pentamethylcyclopentadienyl)(k2-C,N-3-methyl-1-
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
(2-picolyl)-4,5-dichloroimidazol-2-ylidene)ruthenium(II)
Hexa-
90.67(3)
90.00
fluorophosphate (3f). The reaction was carried out with 1f (65 mg,
0.1 mmol). The product was a brownish microcrystalline solid. Yield:
5917(2)
4
1
61 mg, 98%. H NMR (acetone-d6, 600 MHz, SiMe4): δ 8.92 (d,
3JHH = 5.48 Hz, 1H, Hpy), 8.12 (t, 1H, 3JHH = 7.74 Hz, 1H, Hpy), 7.99
(d, 3JHH = 7.63 Hz, 1H, Hpy), 7.52 (t, 3JHH = 6.55 Hz, 1H, Hpy), 5.77
F
calcd (g cmꢀ3
μ(Mo Kα) (mmꢀ1
)
1.613
1.585
2
2
)
0.415
0.436
(d, JHH = 15.96 Hz, 1H, Hbridge), 4.79 (d, JHH = 15.72 Hz, 1H,
Hbridge), 3.92 (s, 3H, NCH3), 1.83 (s, 15H, (C5(CH3)5). 13C{1H}
NMR (acetone-d6, 150 MHz, SiMe4): δ 204.34 (CO), 183.34
(CimidRu); 160.27 (Cpy), 156.31 (Cpy), 140.87 (Cpy), 127.86 (Cpy),
126.43 (Cpy), 118.51 (Cimid), 117.68 (Cimid), 96.16 (C5(CH3)5),
52.88 (CH2), 36.76 (NCH3), 10.08 (C5(CH3)5). IR (Nujol, cmꢀ1): ν
1937 (CO). Anal. Calcd for C21H24Cl2F6N3OPRu: C, 38.72; H, 3.71;
N, 6.45. Found: C, 38.76; H, 3.68; N, 6.49.
F(000)
1316
2840.8
maxꢀmin transmission
factors
0.955ꢀ0.788
1.000ꢀ0.792
θ range for data
collection (deg)
no. of rflns collected
no. of unique rflns
1.16 < θ <
25.09
1.91 < θ <
25.04
18 176
12 034
9179
10 356
Crystal Structure Analysis. Crystals of 2a,b suitable for X-ray
structural determination were mounted on glass fibers and then
transferred to the cold nitrogen gas stream of a Bruker Smart APEX
CCD three-circle diffractometer (T = 100 K) with a sealed-tube source
and graphite-monochromated Mo Kα radiation (α = 0.710 73 Å) at the
Servicio Central de Ciencia y Tecnología de la Universidad de Cꢀadiz.
Four sets of frames were recorded over a hemisphere of the reciprocal
space by ω scans with δ(ω) = 0.30 and an exposure of 10 s per frame.
Correction for absorption was applied by scans of equivalents using the
SADABS program.51 An insignificant crystal decay correction was also
applied. The structures were solved by direct methods and refined on F2
by full-matrix least squares (SHELX97) by using all unique data.52 All
non-hydrogen atoms were refined anisotropically with hydrogen atoms
included in calculated positions (riding model). In each case two
disordered CF3 groups in the anion were refined split into two
complementary orientations using displacement parameter restraints.
For 2b dichloromethane (56%) and diethyl ether (44%) solvates were
found disordered with complementary occupation factors. The program
ORTEP-3 was used for plotting.53 Table 4 summarizes the crystal data
and data collection and refinement details for 2a,b. CCDC
833091ꢀ833092 contain supplementary crystallographic data for this
paper. These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
(Rint = 0.0437)
7324
(Rint = 0.0363)
9256
no. of obsd rflns (I > 2σI)
no. of params
784
876
final R1, wR2 values (I > 2σI)
0.0671,
0.1670
0.0497,
0.1196
final R1, wR2 values (all data)
0.0843,
0.1783
0.0570,
0.1242
residual electron
+0.341, ꢀ0.634
+1.110, ꢀ0.863
density peaks (e Åꢀ3
)
Carbonyl(η5-pentamethylcyclopentadienyl)(k2-C,N-3-mesityl-1-
(2-picolyl)imidazol-2-ylidene)ruthenium(II) Hexafluorophosphate
(3d). The reaction was carried out with 1d (70 mg, 0.1 mmol). The
product was a brownish microcrystalline solid. Yield: 65 mg, 96%. 1H
3
NMR (CD2Cl2, 400 MHz, SiMe4): δ 8.59 (d, JHH = 5.57 Hz, 1H,
Hpy), 7.94 (t, 1H, 3JHH = 7.69 Hz, 1H, Hpy), 7.85 (d, 3JHH = 7.61 Hz,
1H, Hpy), 7.68 (d, 3JHH = 2.06 Hz, 1H, Himid backbone), 7.27 (t, 3JHH
=
6.51 Hz, 1H, Hpy), 7.06 (s, 1H, Hmes), 6.97 (s, 1H, Hmes), 6.95 (d,
2
3JHH = 1.76 Hz, 1H, Himid backbone), 5.63 (d, JHH = 15.53 Hz, 1H,
2
Hbridge), 4.73 (d, JHH = 15.23 Hz, 1H, Hbridge), 2.35 (s, 3H, CH3),
2.13 (s, 3H, CH3), 6.68 (s, 3H, CH3), 1.57 (s, 15H, (C5(CH3)5).
13C{1H} NMR (CD2Cl2, 100 MHz, SiMe4): δ 205.19 (CO), 182.07
(CimidRu), 159.07 (Cpy), 156.88 (Cpy), 139.910 (Cpy), 139.88
(NCmes), 136.91 (Cmes), 135.78 (Cmes), 134.69 (Cmes), 129.55
(Cmes), 128.94 (Cmes), 127.17 (Cpy), 125.25 (Cpy), 124.47 (Cimid),
124.16 (Cimid), 95.23 (C5(CH3)5), 55.54 (CH2), 21.19 (CH3), 18.84
(CH3), 18.62 (CH3), 10.16 (C5(CH3)5). IR (Nujol, cmꢀ1): ν 1928
(CO). Anal. Calcd for C29H34F6N3OPRu: C, 50.73; H, 4.99; N, 6.12.
Found: C, 50.70; H, 5.02; N, 6.15.
Typical Procedure for Catalytic Transfer Hydrogenation.
Ketone or imine (2.0 mmol), catalyst 0.1% (0.002 mmol), KOH (0.2
mmol), 1,3,5-trimethoxybenzene (0.5 mmol), and iPrOH (5 mL) were
placed in a 10 mL vial and stirred on a prehetaed oil bath (82 °C).
Aliquots (0.2 mL) were taken at fixed times, quenched in Et2O (3 mL),
and filtered through a short pad of SiO2. The filtrate was subjected to
GC-MS and 1H NMR analysis. For TOF50 measurements the catalyst
5800
dx.doi.org/10.1021/om200665f |Organometallics 2011, 30, 5793–5802

Organometallics
ARTICLE
loading was 1% (0.02 mmol). The substrate was preheated at 82 °C for
5 min before catalyst and base were added. All data reported are averages
of at least two runs.
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’ ASSOCIATED CONTENT
S
Supporting Information. Table giving catalytic screen-
b
ing results and CIF files giving crystallographic data for com-
pounds 2a,b. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: pedro.valerga@uca.es.
(9) (a) Paꢁzikꢀy, M.; Loos, A.; Ferreira, M. J.; Serra, D.; Vinokurov, N.;
Rominger, F.; J€akel, C.; Hashmi, A. S. K.; Limbach, M. Organometallics
2010, 29, 4448–4458. (b) Binobaid, A.; Iglesias, M.; Beetstra, D. J.;
Kariuki, B.; Dervisi, A.; Fallis, I. A.; Cavell, K. J. Dalton Trans.
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Olivꢀan, M.; O~nate, E. Organometallics 2007, 26, 6556–6563. (g) Wright,
J. A.; Danopoulos, A. A.; Motherwell, W. B.; Carroll, R. J.; Ellwood, S.
J. Organomet. Chem. 2006, 691, 5204–5210. (h) Tulloch, A. A. D.;
Danopoulos, A. A.; Kleinhez, A.; Light, M. E.; Hursthouse, M. B.;
Eastham, G. Organometallics 2001, 20, 2027–2031.
(10) (a) Stylianides, N.; Danopoulos, A. A.; Tsoureas, N. J. Organo-
met. Chem. 2005, 690, 5948–5958. (b) Song, G.; Zhang, Y.; Li, X.
Organometallics 2008, 27, 1936–1943. (c) Danopoulos, A. A.; Pugh, D.;
Wright, J. A. Angew. Chem., Int. Ed. 2008, 47, 9765–9767.
(11) (a) Kascatan-Nebioglu, A.; Panzner, M. J.; Tessier, C. A.;
Cannon, C. L.; Youngs, W. J. Coord. Chem. Rev. 2007, 251, 884–895.
(b) Catalano, V.; Etogo, A. O. J. Organomet. Chem. 2005, 690,
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’ ACKNOWLEDGMENT
We thank the Spanish MICINN (Projects CTQ2007-60137/
BQU and CTQ2010-15390) and “Junta de Andalucía” (PAI-
FQM188 and Project of Excellence P08-FQM-03538) for finan-
cial support and Johnson Matthey plc for generous loans of
ruthenium trichloride. F.E.F. acknowledges the Spanish MI-
CINN for an FPI fellowship (BES-2008-006635).
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(44) Work in progress. Relevant spectral data are as follows. H
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7.45 (br s, 8H, BPh4), 7.27 (t, 3JHH = 7.32 Hz, 1H, Hpy), 7.00 (t, 3JHH
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=
=
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6.59 Hz, 1H, Hpy), 6.69 (d, 3JHH = 7.91 Hz, 1H, Hpy), 2.83, 2.69 (m, 1H
each, PCH2), 2.29, 2.21 (m, 1H each, P(CH(CH3)2)2), 1.73 (d, 15 H,
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BPh4), 162.12 (Cpy), 154.31 (Cpy), 138.88 (Cpy), 136.20 (BPh4),
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1
1
(C5(CH3)5), 35.74 (d, JCP = 24.47 Hz, PCH2), 25.68 (d, JCP
=
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