Transfer hydrogenation of ketones by ruthenium complexes bearing benzimidazol-2-ylidene ligands

Article abstract of DOI:10.1002/ejic.201000181

A series of benzimidazolium ligand precursors were metalated with [RuCl₂(p-cymene)]₂ to give ruthenium(II) N-heterocyclic carbene complexes. All compounds were fully characterized by elemental analyses, ¹H NMR, ¹³

Full text of DOI:10.1002/ejic.201000181

FULL PAPER
DOI: 10.1002/ejic.201000181
Transfer Hydrogenation of Ketones by Ruthenium Complexes Bearing
Benzimidazol-2-ylidene Ligands
[a]
[b]
[a]
[a]
˙
Nevin Gürbüz, Sedat Yasar, Emine Özge Özcan, Ismail Özdemir,* and
¸
Bekir Çetinkaya[c]
Keywords: Nitrogen heterocycles / Carbene ligands / Ruthenium / Hydrogenation / Ketones
A series of benzimidazolium ligand precursors were metal-
ated with [RuCl2(p-cymene)]2 to give ruthenium(II) N-hetero-
cyclic carbene complexes. All compounds were fully charac-
terized by elemental analyses, 1H NMR, 13C NMR, and IR
spectroscopy. The new benzimidazol-2-ylidene complexes
have been found to be effective catalysis for the transfer hy-
drogenation of ketones by using 2-propanol as the hydrogen
source in the presence of KOH.
Recently, research has also been devoted to the synthesis
of functionalized ligands containing NHC moieties to mod-
ify ligand properties and catalytic activities.[14] The first ap-
plication of NHC complexes for the transfer hydrogenation
reaction was reported by Nolan in 2001.[15] With regard to
transfer hydrogenations, different carbene or carbene–phos-
phane systems containing Rh,[16] Ir,[16,17] Ru,[18] and Ni[19]
have been reported.
Previously, our laboratory reported the application of
imidazolidin-2-ylidene ruthenium complexes I–II and benz-
imidazole ruthenium complexes III in the transfer hydro-
genation of aromatic ketones.[20]
Introduction
Hydrogenation and transfer hydrogenation of unsatu-
rated compounds are among the most important synthetic
reactions not only from an academic standpoint but from
an industrial standpoint as well, because these processes are
operationally simple, environmentally friendly, and econ-
omic.[1] When compared to hydride reagents and hydrogen,
these methods offer simple and safe operation and low
costs, which are important, particularly on large-scale prep-
arations. The processes involve hydrogen transfer from a
donor to an unsaturated compound.[2]
Transfer hydrogenation of ketones catalyzed by metal
complexes is one of the most important route to reduce
ketones to alcohols, and it has been extensively investi-
gated.[3] A broad range of alcohols are accessible by transfer
hydrogenation under mild reaction conditions in the pres-
ence of various metal catalysts.[4] A large number of ruthe-
nium complexes have been reported as catalyst precursors
for the transfer hydrogenation of ketones and have shown
high activity.[5] Several recent examples of ruthenium com-
plexes bearing phosphanes,[6] N-heterocyclic carbenes
(NHCs),[7] diamines,[8] diaminodiphosphanes or aminodi-
phosphanes,[9] amine–bis(phenolate)s,[10] chiral phospha-
nes,[11] nitrogen-containing chiral ligands,[12] and nitrogen-
containing heterocyclic ligands[13] have become the most
prominent members for the reduction of ketones in high
yields.
In view of the growing interest in the catalytic activities
of ruthenium complexes to act as efficient catalysts in the
transfer hydrogenation of ketones, we herein report the syn-
thesis of new benzimidazol-2-ylidene ruthenium(II) com-
plexes. The characterization of the complexes was ac-
complished by analytical and spectral methods. Further, the
synthesized complexes were effectively used as catalysts in
the transfer hydrogenation of ketones in the presence of 2-
propanol and KOH as base.
[a] Inönü University, Faculty Science and Art, Department of
Chemistry,
44280 Malatya, Turkey
Results and Discussion
E-mail: iozdemir@inonu.edu.tr
[b] Gaziosmanpas¸a University, Faculty Science and Art,
Department of Chemistry,
Preparation of Benzimidazolium Salts
Tokat, Turkey
Dialkylbenzimidazolium salts 1a–e were prepared ac-
[c] Ege University, Faculty Science, Department of Chemistry,
35100 Bornova-Izmir, Turkey
cording to known methods[21] as conventional NHC precur-
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FULL PAPER
sors. Functionalized or bulky benzimidazolium salts 1a–e not have to be isolated, thus simplifying the reaction
were obtained upon reaction of a benzyl halides with 1- workup when the aim is to prepare the metal complex.[23]
aklylbenzimidazole in dimethylformamide and isolated in This method was used for the preparation of complexes 2a–
78–91% yield (Scheme 1).
e. The carbene ligand, arising from deprotonation of benz-
imidazolium salts 1a–e with the use of Cs2CO3 according
to the literature,[24] was treated with [RuCl2(p-cymene)]2 in
toluene at 110 °C. After 5 h, the reaction was complete and
mononuclear neutral ruthenium(II) complexes 2a–e were
obtained as red-brown crystalline solids in 72–87% yield
(Scheme 2). Air- and moisture-stable ruthenium carbene
complexes 2a–e were soluble in halogenated solvents and
insoluble in nonpolar solvents.
Scheme 1. Synthesis of 1,3-dialkylbenzimidazolium salts.
The salts are air and moisture stable both in the solid
state and in solution and soluble in chlorinated solvents,
alcohols, and water. Benzimidazolium salts 1a–e were iso-
lated as solids in very good yields and fully characterized by
1H NMR, 13C NMR, and IR spectroscopy and elemental
analyses, and their melting points were determined. 13C
NMR chemical shifts were consistent with the proposed
structure; the imino carbon atom appeared as a typical sin-
glet in the 1H-decoupled mode at 143.7, 143.8, 144.8, 152.7,
and 142.8 ppm, respectively, for benzimidazolium salts 1a–
e.
Scheme 2. Synthesis of ruthenium–carbene complexes.
Complexes 2a–e (except for 2c) with the aryl group η6-
coordinated to the ruthenium atom was obtained in good
yields (Scheme 2). These results show that Cs2CO3 is able
to generate a ruthenium-coordinated benzimidazolinylidene
group in refluxing toluene and that the p-cymene ligand can
be displaced by an intramolecular aryl group. Complexes
2a–e, which are very stable in the solid state, were charac-
terized by analytical and spectroscopic techniques. Ruthe-
nium complexes exhibit a characteristic νNCN band typi-
cally at 1404, 1418, 1409, 1410, and 1404 cm–1, respectively,
for 2a–e.[24–26] The 13C NMR chemical shifts provide a use-
ful diagnostic tool for this type of metal carbene complex.
The chemical shifts for the carbon atom fall in the 182–
186 ppm region and are similar to those found in other ru-
thenium–carbene complexes.[24–26]
1
The H NMR spectra of the benzimidazolium salts fur-
ther supported the assigned structures; the resonances for
C(2)-H were observed as sharp singlets at 11.63, 11.48,
11.83, 11.85, and 11.76 ppm, respectively, for 1a–e. The IR
data for benzimidazolium salts 1a–e clearly indicate the
presence of the –C=N– group with a ν(C=N) vibration at
1557, 1576, 1590, 1571, and 1580 cm–1, respectively, for 1a–
e. The NMR values are similar to those found for other 1,3-
dialkylbenzimidazolium salts.[22]
Catalytic Transfer Hydrogenation of Ketones
Preparation of Ruthenium–Carbene Complexes 2a–e
Catalytic reduction is preferred to stoichiometric re-
The in situ deprotonation of an azolium salt to produce duction for large-scale industrial uses, and the catalytic hy-
the desired NHC has the advantage that the carbene does drogenation of ketones is well known.[27] Hydrogen gas
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Transfer Hydrogenation of Ketones by Ruthenium Complexes
presents considerable safety hazards, especially for large- Table 1. Transfer hydrogenation of ketones catalyzed by 2a–e.[a]
scale reactions;[28] the use of a solvent that can donate hy-
drogen atoms overcomes this difficulty. 2-Propanol is a
popular reactive solvent for transfer hydrogenation, as it is
easy to handle (b.p. 82 °C) and is relatively nontoxic, envi-
ronmentally benign, and inexpensive. The volatile acetone
product can also be easily removed to shift an unfavorable
equilibrium.[5b] Owing to their efficiency in the transfer hy-
drogenation of acetophenone derivatives, ruthenium(II)
complexes 2a–e were further investigated in the transfer hy-
drogenation of various methyl aryl ketones.
Ruthenium(II) complexes 2a–e catalyze the reduction of
ketones to the corresponding alcohols through hydrogen
transfer from 2-propanol with KOH as the promoter. As
the starting point, the performance of the catalysts in the
transfer hydrogenation was screened by using acetophenone
as a model substrate [Equation (1)].
(1)
In a typical experiment, the preformed, isolated crystal-
line catalyst (0.01 mmol) was dissolved in 2-propanol. After
the catalyst had completely dissolved, acetophenone
(1.00 mmol) and a base (4 mmol) were added, and the reac-
tion was heated at 80 °C. The reactions were conducted at
a substrate/catalyst/base (S/C/base) molar ratio of 1:0.01:4.
For the choice of base, we surveyed Cs2CO3, K2CO3, KOH,
NaOH, and tBuOK. Addition of bases like KOH or NaOH
led to similar final conversions, but the highest rate was
observed when KOH was employed. In the absence of a
base, transfer hydrogenation of the ketones was not ob-
served. Under the reaction conditions, complex 2d proved
to be more effective than 2a, 2b, 2c, and 2e. The reduction
of acetophenone with 2d was complete within 1 h in 97%
conversion. In contrast, acetophenone was reduced within
1 h with the use of 2a, 2b, 2c, and 2e in 90, 90, 85, and 91%
conversion, respectively (Table 1, Entries 1–5).
A variety of ketones were transformed into the corre-
sponding secondary alcohols. Typical results are shown in
Table 1. Under those conditions, p-methoxyacetophenone,
o-methoxyacetophenone, m-methoxyacetophenone, p-fluo-
roacetophenone, and 3,4,5-trimethoxyacetophenone re-
acted very cleanly and in goods yields with 2-propanol
(Table 1, Entries 10, 22, 25, and 15). Enhancement in ac-
tivity, although less significant, was further observed by em-
ploying o-methoxyacetophenone instead of p-methoxyace-
pounds was checked by GC and GC–MS and yields are based on
tophenone (Table 1 Entries 6–10, 20–22).
[a] Reaction conditions: substrate (1.0 mmol), iPrOH (10 mL),
KOH (4 mmol), Ru–NHC (0.01 mmol), 80 °C, 1 h. Purity of com-
ketones.
As shown in Table 1, the reduction is more efficient for
4-fluoroacetophenone than for 2-chloroacetophenone, and
among the complexes, 2e was the most active, giving 96% The conversions of ketones with bulky substituents on the
conversion after 1 h (Table 1, Entries 15 and 19). The ruthe- aromatic ring were not observed or were slightly lower. For
nium complexes also catalyzed the transfer hydrogenation example, when a ketone with a pentamethyl group on the
of benzophenone very effectively (Table 1 Entries 34–36). aromatic ring was used in the transfer hydrogenation, con-
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¸
FULL PAPER
[m, 8 H, CH2C6H4(CH3)-4 and C6H4], 11.63 (s, 1 H, NCHN) ppm.
13C NMR (100.5 MHz, CDCl3): δ = 20.3 [CH2C6H2(CH3)3-2,6],
21.1 [CH2C6H2(CH3)3-4], 21.2 [CH2C6H4(CH3)-4], 51.3 [CH2C6H2-
(CH3)3-2,4,6], 47.4 [CH2C6H4(CH3)-4], 113.8, 125.1, 126.9, 127.1,
128.1, 128.3, 129.9, 130.0, 130.2, 131.4, 131.5, 137.9, 139.3, 139.7
[CH2C6H2(CH3)3-2,4,6, CH2C6H4(CH3)-4, C6H4], 143.7 (NCHN)
ppm. C25H27ClN2 (390.95): calcd. C 76.80, H 6.96, N 7.17; found
C 76.80, H 7.01, N 7.19.
version was not observed (Table 1, Entries 29 and 30), and
when 2,4,6-trimethylphenyl methyl ketone was used, the
conversion was lower (Table 1, Entries 31–33).
Among the tested complexes, complex 2e is highly ef-
ficient in the transfer hydrogenation of ketones to second-
ary alcohols. The data indicate clearly the superiority of the
complexes with pentamethyl benzyl substituents at the ring
nitrogen atom.
1-(3,5-Dimethylbenzyl)-3-(2,3,5,6-tetramethylbenzyl)benzimidazolium
Chloride (1b): Yield: 3.36 g (80%); m.p. 214–215 °C. IR: ν = 1576
˜
(νCN) cm–1. 1H NMR (399.9 MHz, CDCl3): δ = 2.20 [s, 12 H,
CH2C6H4(CH3)2-3,5; CH2C6H(CH3)4-3,5], 2.24 [s, 6 H, CH2C6H-
(CH3)4-2,6], 5.82 [s, 2 H, CH2C6H3(CH3)2-3,5], 5.93 [s, 2 H,
Conclusions
The above results show that benzimidazolinylidene li-
gands containing an arylmethyl-N group (except for 1c) on
reaction with [RuCl2(p-cymene)]2 displace the p-cymene li-
gand to give chelate ruthenium complexes. The complexes
show high activity in the catalytic transfer hydrogenation of
ketones with the use of 2-propanol in the presence of KOH.
Complex 2e is the most active complex. The procedure is
simple and efficient towards various aryl ketones. Although
all of the complexes are active catalysts for the transfer hy-
drogenation of ketones, conversion was not observed with
very substituted ketones such as 2Ј,3Ј,4Ј,5Ј,6Ј-pentameth-
ylacetophenone. Also, we obtained moderate yields with
2Ј,4Ј,6Ј-trimethylacetophenone. We are currently investiga-
ting the scope and application of these complexes as cata-
lysts for various organic reactions.
CH2C6H(CH3)4-2,3,5,6], 6.92–7.56 [m,
8 H, CH2C6H(CH3)3-
2,3,5,6; CH2C6H3(CH3)2-3,5 and C6H4], 11.48 (s, 1 H, NCHN)
ppm. 13C NMR (100.5 MHz, CDCl3): δ = 16.1 [CH2C6H(CH3)4-
2,6], 21.2 [CH2C6H3(CH3)2-3,5 and CH2C6H(CH3)4-3,5], 48.0
[CH2C6H4(CH3)2-3,5], 51.5 [CH2C6H4(CH3)2-2,3,5,6], 113.8, 125.7,
126.9, 127.1, 127.8, 130.7, 131.5, 131.6, 132.8, 133.6, 134.0, 135.1,
138.9 [CH2C6H4(CH3)2-3,5; CH2C6H(CH3)4-2,3,5,6 and C6H4],
143.8 (NCHN) ppm. C27H31ClN2 (419.00): calcd. C 77.40, H 7.46,
N 6.69; found C 77.45, H 7.42, N 6.72.
1,3-Bis(3-methylbenzyl)benzimidazolium Chloride (1c): Yield: 2.83 g
(78%); m.p. 135–136 °C. IR: ν = 1590 (νCN) cm–1. 1H NMR
˜
(399.9 MHz, CDCl3): δ = 2.28 [s, 6 H, CH2C6H4(CH3)-3], 5.82 [s,
2 H, CH2C6H4(CH3)-3], 7.09–7.98 [m, 12 H, CH2C6H4(CH3)-3 and
C6H4], 11.83 (s, 1 H, NCHN) ppm. 13C NMR (100.5 MHz,
CDCl3): δ = 21.5 [CH2C6H2(CH3)3-3], 51.8 [CH2C6H4(CH3)-3],
125.5, 129.0, 129.4, 130.2, 131.6, 132.8, 139.5 [CH2C6H4(CH3)-3
and C6H4], 144.8 (NCHN) ppm. C23H23ClN2 (362.90): calcd. C
76.12, H 6.39, N 7.72; found C 76.10, H 6.36, N 7.75.
Experimental Section
1,3-Bis(4-tert-butylbenzyl)benzimidazolium Bromide (1d): Yield:
General Methods: All reactions for the preparation benzimidazol-
ium salts 1 and ruthenium–NHC complexes 2 were carried out un-
der an atmosphere of argon in flame-dried glassware by using stan-
dard Schlenk techniques. The solvents used were purified by distil-
lation over the drying agents indicated and were transferred under
an atmosphere of argon: Et2O (Na/K alloy), CH2Cl2 (P4O10), hex-
ane, toluene (Na). Melting points were determined in glass capillar-
ies under air with an Electrothermal-9200 melting point apparatus.
FTIR spectra were recorded as KBr pellets in the range 400–
4.23 g (89%); m.p. 236–237 °C. IR: ν = 1571 (νCN) cm–1. 1H NMR
˜
(399.9 MHz, CDCl3): δ = 1.25 {s, 18 H, CH2C6H4[C(CH3)3-4],}
5.82 {s,
2 H, CH2C6H4[C(CH3)3-4]}, 7.35–7.46 {m, 12 H,
CH2C6H4[C(CH3)3-4] and C6H4}, 11.85 (s, 1 H, NCHN) ppm. 13C
NMR (100.5 MHz, CDCl3): δ = 31.4 {CH2C6H4[C(CH3)3-4]}, 34.9
{CH2C6H4[C(CH3)3-4]}, 51.5 [CH2C6H4(CH3)2-3,5], 114.0, 126.5,
127.3, 128.4, 129.8 and 131.6 {CH2C6H4[C(CH3)3-4] and C6H4},
152.7 (NCHN) ppm. C29H35BrN2 (491.51): calcd. C 70.87, H 7.18,
N 5.70; found C 70.85, H 7.20, N 5.77.
1
4000 cm–1 with an ATI UNICAM 1000 spectrometer. H and 13C
NMR spectra were recorded by using a Varian AS 400 Merkur
spectrometer operating at 400 (1H) and 100 MHz (13C) in CDCl3
and [D6]DMSO with tetramethylsilane as an internal reference.
Column chromatography was performed by using silica gel 60 (70–
230 mesh). Elemental analyses were performed by Turkish Re-
search Council (Ankara, Turkey) Microlab.
1-(Methoxyethyl)-3-(2,3,4,5,6-pentamethylbenzyl)benzimidazolium
Bromide (1e): Yield: 3.14 g (84%); m.p. 186–187 °C. IR: ν = 1580
˜
(νCN) cm–1. 1H NMR (399.9 MHz, CDCl3): δ = 2.18 [s, 6 H,
CH2C6(CH3)5-2,6], 2.25 [s, 3 H, CH2C6(CH3)5-4], 2.23 [s, 6 H,
CH2C6(CH3)5-3,5], 3.30 (s, 3 H, OCH3), 3.89 (t, J = 4.5 Hz, 2 H,
NCH2CH2O), 4.96 (t, J = 4.5 Hz, 2 H, NCH2CH2O), 5.79 [s, 2 H,
CH2C6(CH3)5-2,3,4,5,6], 7.29–7.93 (m, 4 H, C6H4), 11.76 (s, 1 H,
NCHN) ppm. 13C NMR (100.5 MHz, CDCl3): δ = 17.0, 17.1
[CH2C6(CH3)5-2,3,5,6], 17.3 [CH2C6(CH3)5-4], 47.9 [CH2C6-
(CH3)5-2,3,4,5,6], 70.5 (OCH3), 59.0 (NCH2CH2O), 47.9 (NCH2-
CH2O), 113.11, 114.3, 124.8, 127.0, 131.2, 132.5, 133.6, 134.0,
137.4 [CH2C6(CH3)5-2,3,4,5,6 and C6H4], 142.8 (NCHN) ppm.
C22H29BrN2O (417.38): calcd. C 63.31, H 7.00, N 6.71; found C
63.35, H 7.05, N 6.76.
General Method for the Preparation of Benzimidazolium Salts: To a
solution of N-alkylbenzimidazole (10.0 mmol) in DMF (5 mL) was
added slowly the alkyl or aryl halide (10.0 mmol), and the resulting
mixture was stirred at room temperature for 5 h. Ethyl ether
(10 mL) was added to obtain a white crystalline solid, which was
filtered off. The solid was washed with diethyl ether (3ϫ10 mL)
and dried under vacuum, and the crude product was recrystallized
from ethanol/diethyl ether.
1-(2,4,6-Trimethylbenzyl)-3-(4-methylbenzyl)benzimidazolium Chlo-
General Method for the Preparation of Ruthenium Complexes 2a–e:
ride (1a): Yield: 3.21 g (82%); m.p. 216–217 °C. IR: ν = 1557
A
suspension of benzimidazolium salt (2.10 mmol), Cs2CO3
˜
(νCN) cm–1. 1H NMR (399.9 MHz, CDCl3): δ = 2.19 [s, 6 H,
(2.14 mmol), and [RuCl2(p-cymene)]2 (0.82 mmol) was heated un-
CH2C6H2(CH3)3-2,6], 2.26 [s, 6 H, CH2C6H2(CH3)3-4, CH2C6H4- der reflux in degassed toluene (20 mL) for 5 h. The reaction mix-
(CH3)-4], 5.84 [s, 2 H, CH2C6H2(CH3)3-2,4,6], 5.85 [s, 2 H, ture was then filtered while hot, and the volume was reduced to
CH2C6H4(CH3)-4], 6.89 [s, 2 H, CH2C6H2(CH3)3-2,4,6], 7.09–7.55 about 10 mL before addition of n-hexane (15 mL). The precipitate
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Transfer Hydrogenation of Ketones by Ruthenium Complexes
formed was crystallized from CH2Cl2/hexane (5:15 mL) to give red-
brown crystals.
CDCl3): δ = 2.08 [s, 6 H, CH2C6(CH3)5-2,6], 2.29 [s, 6 H,
CH2C6(CH3)5-4], 2.02 [s, 3 H, CH2C6(CH3)5-3,5], 3.28 (s, 3 H,
OCH3), 3.76 (t, J = 4.8 Hz, 2 H, NCH2CH2O), 4.67 (t, J = 4.8 Hz,
2 H, NCH2CH2O), 5.06 [s, 2 H, CH2C6(CH3)5-2,3,4,5,6], 7.70–7.27
(m, 4 H, C6H4) ppm. 13C NMR (100.5 MHz, CDCl3): δ = 15.0,
15.7 [CH2C6(CH3)5-2,3,5,6], 14.9 [CH2C6(CH3)5-4], 48.0 [CH2C6-
(CH3)5-2,3,4,5,6], 65.9 (OCH3), 46.4 (NCH2CH2O), 58.8
(NCH2CH2O), 94.5, 98.1, 132.9, [CH2C6(CH3)5-2,3,4,5,6] 107.8,
109.1, 113.4, 123.1, 123.5, 136.0 (C6H4), 186.2 (Ccarb) ppm.
C22H28Cl2N2ORu (508.45): calcd. C 51.97, H 5.55, N 5.51; found
C 51.99, H 5.58, N 5.55.
Dichloro-[1-(2,4,6-trimethylbenzyl)-3-(4-methylbenzyl)benzimidazol-
2-ylidene]ruthenium(II) (2a): Yield: 0.56 g (84%); m.p. 283–284 °C.
1
IR: ν = 1404 (νCN) cm–1. H NMR (399.9 MHz, CDCl3): δ = 2.19
˜
[s, 6 H, CH2C6H2(CH3)3-2,6], 2.15 [s, 3 H, CH2C6H2(CH3)3-4] 2.19
[s, 3 H, CH2C6H4(CH3)-4], 5.50 [s, 2 H, CH2C6H2(CH3)3-2,4,6],
5.11 [s, 2 H, CH2C6H4(CH3)-4], 5.55 [s, 2 H, CH2C6H2(CH3)3-
2,4,6], 6.94–7.87 [m, 8 H, CH2C6H4(CH3)-4 and C6H4] ppm. 13C
NMR (100.5 MHz, CDCl3): δ = 16.9 [CH2C6H2(CH3)3-2,6], 17.5
[CH2C6H2(CH3)3-4], 21.2 [CH2C6H4(CH3)-4], 45.2 [CH2C6H2-
(CH3)3-2,4,6], 51.4 [CH2C6H4(CH3)-4], 90.1, 93.3, 98.3, 101.1
[CH2C6H2(CH3)3-2,4,6], 110.9, 112.4, 123.3, 123.8, 127.9, 129.0,
Typical Procedure for the Catalytic Transfer Hydrogenation of
Ketones: Under an inert atmosphere, a mixture containing the
ketone (1 mmol), ruthenium catalyst 2a–e (0.01 mmol), and KOH
(4 mmol) was heated at reflux in iPrOH (10 mL) for 1 h. The sol-
vent was then removed under reduced pressure, and the product
distribution was determined by 1H NMR spectroscopy and GC
and GC–MS.
133.5, 134.0,134.5, 136.8 [CH2C6H4(CH3)-4, C6H4], 185.3 (Ccarb
)
ppm. C25H26Cl2N2Ru (526.46): calcd. C 57.03, H 4.98, N 5.32;
found C 57.05, H 5.00, N 5.36.
Dichloro-[1-(2,3,5,6-tetramethylbenzyl)-3-(3,5-dimethylbenzyl)benz-
imidazol-2-ylidene]ruthenium(II) (2b): Yield: 0.58 g (88%); m.p.
384–385 °C. IR: ν = 1418 (νCN) cm–1 1H NMR (399.9 MHz,
.
˜
CDCl3): δ = 2.14 [s, 12 H, CH2C6H4(CH3)2-3,5; CH2C6H(CH3)4-
3,5], 2.0 [s, 6 H, CH2C6H(CH3)4-2,6], 5.34 [s, 2 H, CH2C6H3-
(CH3)2-3,5], 5.51 [s, 2 H, CH2C6H(CH3)4-2,3,5,6], 6.54–7.68 [m, 8
H, CH2C6H(CH3)3-2,3,5,6; CH2C6H3(CH3)2-3,5 and C6H4] ppm.
13C NMR (100.5 MHz, CDCl3): δ = 13.8 [CH2C6H(CH3)4-2,6],
18.2 and 21.4 [CH2C6H3(CH3)2-3,5 and CH2C6H(CH3)4-3,5], 46.3
[CH2C6H4(CH3)2-3,5], 51.5 [CH2C6H4(CH3)2-2,3,5,6], 85.0, 98.9,
109.6, 112.4, 122.0, 124.5, 126.0, 128.4, 129.0, 133.4, 134.4, 135.5,
137.9 [CH2C6H4(CH3)2-3,5; CH2C6H(CH3)4-2,3,5,6 and C6H4],
185.4 (Ccarb) ppm. C27H30Cl2N2Ru (554.52): calcd. C 58.48, H 5.45,
N 5.05; found C 58.44, H 5.41, N 5.01.
Acknowledgments
This work was financially supported by the Technological and
Scientific Research Council of Turkey TUBITAK (107T098) and
˙
Inönü University Research Fund.
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Dichloro-[1,3-bis(3-methylbenzyl)benzimidazol-2-ylidene](p-cymene)-
ruthenium(II) (2c): Yield: 0.72 g (72%); m.p. 294–295 °C. IR: ν =
˜
1
1609 (νCN) cm–1. H NMR (399.9 MHz, CDCl3): δ = 1.30 [d, J =
13.8 Hz, 6 H, p-CH3C6H4CH(CH3)2], 1.26 [s, 6 H, CH2C6H4(CH3)-
3], 1.27 [s, 3 H, p-CH3C6H4CH(CH3)2], 1.63 [p, J = 6.6 Hz, 1 H,
p-CH3C6H4CH(CH3)2], 5.13 [s, 4 H, CH2C6H4(CH3)-3], 4.81–7.31
[m, 16 H, CH2C6H4(CH3)-3, p-CH3C6H4CH(CH3)2 and C6H4]
ppm. 13C NMR (100.5 MHz, CDCl3): δ = 19.1 [p-CH3C6H4CH-
(CH3)2], 21.5 [CH2C6H2(CH3)3-3 and CH3C6H4CH(CH3)2], 29.7
[p-CH3C6H4CH(CH3)2], 53.0 [CH2C6H4(CH3)-3], 75.4, 87.4, 99.8,
109.6, 113.3, 114.6, 123.4, 124.0, 125.0, 128.6, 133.0, 134.8, 136.4,
137.8 5 [CH2C6H4(CH3)-3, p-CH3C6H4CH(CH3)2 and C6H4],
182.1 (Ccarb) ppm. C32H35Cl2N2Ru (619.61): calcd. C 62.03, H 5.69,
N 4.52; found C 62.06, H 5.73, N 4.56.
Dichloro-[1,3-bis(4-tert-butylbenzyl)benzimidazol-2-ylidene]rutheni-
um(II) (2d): Yield: 0.50 g (87%); m.p. 314–315 °C. IR: ν = 1609
˜
(νCN) cm–1 1H NMR (399.9 MHz, CDCl3): δ = 1.26 {s, 9 H,
.
CH2C6H4[C(CH3)3-4]}, 1.54 {s, 9 H, CH2C6H4[C(CH3)3-4]}, 4.99
{m, 2 H, coord. CH2C6H4[C(CH3)3-4]}, 6.20 {m, 2 H, CH2C6H4[C-
(CH3)3-4]}, 5.83–5.31{m, 4 H, coord. CH2C6H4[C(CH3)3-4]} 7.35–
7.46 {m, 8 H, CH2C6H4[C(CH3)3-4 and C6H4] ppm}. 13C NMR
(100.5 MHz, CDCl3): δ = 31.0 {CH2C6H4[C(CH3)3-4]}, 31.3
{coord. CH2C6H4[C(CH3)3-4]}, 34.4 {CH2C6H4[C(CH3)3-4]}, 35.0
{coord. CH2C6H4[C(CH3)3-4]}, 50.6 [coord. CH2C6H4(CH3)2-3,5],
53.5 [CH2C6H4(CH3)2-3,5], 96.2, 96.6, 99.7, 100.0 {coord.
CH2C6H4[C(CH3)3-4]}, 109.6, 112.4, 113.2, 123.3, 124.0, 125.1,
127.2, 132.9, 133.5, 134.8, {CH2C6H4[C(CH3)3-4 and C6H4]}, 185.3
(Ccarb) ppm. C29H34Cl2N2Ru (582.57): calcd. C 59.79, H 5.88, N
4.81; found C 59.76, H 5.92, N 4.82.
Dichloro-[1-(2,3,4,5,6-pentamethylbenzyl)-3-(2-methoxyethyl)benz-
imidazol-2-ylidene]ruthenium (II) (2e): Yield: 0.91 g (72%); m.p.
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˜
Eur. J. Inorg. Chem. 2010, 3051–3056
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: February 14, 2010
Published Online: May 12, 2010
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Eur. J. Inorg. Chem. 2010, 3051–3056