Heterocyclic carbene complexes of nickel, palladium, and copper(I) as effective catalysts for the reduction of ketones

Article abstract of DOI:10.1007/s10593-012-0947-9

Carbene complexes of nickel, palladium, and copper(I) effectively catalyze the reduction of aromatic ketones under the influence of 2-propanol in the presence of potassium hydroxide. Bis(1,3-dimethyl-benzimidazol-2-ylidene)copper(I) iodide and the polymeric complex of crown-biscarbene with copper(I) iodide show the highest catalytic efficiency.

Full text of DOI:10.1007/s10593-012-0947-9

Chemistry of Heterocyclic Compounds, Vol. 47, No. 12, March, 2012 (Russian Original Vol. 47, No. 12, December, 2011)
HETEROCYCLIC CARBENE COMPLEXES OF NICKEL,
PALLADIUM, AND COPPER(I) AS EFFECTIVE CATALYSTS
FOR THE REDUCTION OF KETONES *
1
1
1
N. I. Korotkikh **, V. Sh. Saberov , A. V. Kiselev ,
1
1
1
N. V. Glinyanaya , K. A. Marichev , T. M. Pekhtereva ,
2
3
1
G. V. Dudarenko , N. A. Bumagin , and O. P. Shvaika
Carbene complexes of nickel, palladium, and copper(I) effectively catalyze the reduction of aromatic
ketones under the influence of 2-propanol in the presence of potassium hydroxide. Bis(1,3-dimethyl-
benzimidazol-2-ylidene)copper(I) iodide and the polymeric complex of crown-biscarbene with copper(I)
iodide show the highest catalytic efficiency.
Keywords: heterocyclic carbene complexes of copper(I), nickel, and palladium, catalysis, reduction of
ketones.
It is known that carbene complexes of transition metals catalyze condensation reactions (Suzuki-
Miyaura, Sonogashira, Stille, Kumada, Mizoroki-Heck reactions), olefin metathesis, reduction of multiple bonds,
olefin polymerization, etc. [1–3]. Stable carbenes are also reactive in transesterification, the Claisen
condensation, and the benzoin and formoin condensations [4]. Especially valuable in this respect are
heterocyclic carbenes and their complexes which have the most stable carbene structures. Among these catalytic
conversions, reduction by a hydrogen transfer from alcohols to the multiple bonds, which includes reduction of
carbonyl compounds, imines and olefins [1], is interesting but rather poorly studied. It is known that these
reactions are catalyzed by rhodium(I-III), iridium(I-III) and ruthenium(I-III) carbene complexes [5–24].
Complexes of the type of compounds 1-9 (Fig.1) which with similar effectiveness noticeably accelerate
reduction of ketones by 2-propanol in alkaline media (hydrogen transfer) should be distinguished among them.
_
*
*
______
Dedicated to the memory of Academician E. Lukevics.
*To whom correspondence should be addressed, e-mail: nkorotkikh@ua.fm.
1
L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, The National Academy of Sciences of
Ukraine, 70, R. Luxemburg ul., Donetsk 83114, Ukraine.
2
Institute of Macromolecular Chemistry, The National Academy of Sciences of Ukraine, 48 Kharkivske
Highway, Kyiv 02160, Ukraine.
3
M. V. Lomonosov Moscow State University, 1/3 Leninskie gory, Moscow 119991, Russia; e-mail:
bumagin@org.chem.msu.ru.
_
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.12, 1854-1864, December, 2011. Original
article received July 7, 2011
009-3122/12/4712-1551©2012 Springer Science+Business Media, Inc.
0
1551

To assess the catalytic activity turnover numbers (TON) and turnover frequencies (TOF) are often used
in literature. In case of the benzophenone reduction by ruthenium complex catalyst 1 TON is equal to 4700, while
–1
TOF is equal to 780 h [16]. Similar process with iridium complex 8 is characterized by TON equal to 1800, and
–
1
TOF equal to 1800 h [18]. When using rhodium complex 9 for catalyzing the benzophenone reduction, the
–
1
highest TON is obtained (10580), however TOF in this case is substantially lower (441 h ) [7]. Reaction time in
case of using this catalyst is still quite long (up to 24 h), and reduction product yields do not exceed 85–86%.
Significant disadvantage of all mentioned catalysts 1–9 is a high price of rhodium, ruthenium and iridium
derivatives.
Bn
Bn
+
H2
C
N
Mes
N
N
N
N
N
N
Cl
Me
N
N
Cl
Ir
Ru
CO
Ir
Cl
N
Br
OH2
OC
Br
N
N
N
Me
Alk
Me
1
2
N
Me
Me
Me
3
i-Pr
Mes
N
N
N
N
I
Cl N
O
N
Ir
Rh
I
M
N
N
X
O
N
N
t-Bu
6
Cl
Mes
4
N
N
t-Bu
i-Pr
5
N Bu
Br
N Rh Br
Br
+
N
N
N
_
BF4
Ir
N
Ir
N
N
R
Cl
N
Bu
7
8
9
6
M = Rh, Ir; 8 R = Alk, Bn
Figure 1. Carbene complexes used as hydrogen transfer catalysts.
The objective of this work is to study the catalytic efficiency of carbenes and carbene complexes of such
transition metals as nickel(II), palladium(II), and copper(I) in the reduction of ketones with 2-propanol in the
presence of potassium hydroxide.
Mono- and biscarbene complexes of copper(I), carbene chelate and biscarbene complexes of nickel and
palladium, and polymeric complexes of copper(I) were used as carbene complex catalysts.
According to our proposed method, monocarbene complex 11 (Scheme 1) was synthesized by reaction
of the salt 10 with copper(I) chloride in acetonitrile in the presence of triethylamine.
1
552

Scheme 1
Bn
Bn
+
CuCl, Et N
3
N
N
Cl
MeCN
CuCl
8
2°C, 2 h
6%
N
N
6
Bn
Bn
1
0
11
Biscarbene complexes 13, 14 (Scheme 2) were obtained by refluxing the solutions of 2H-cyano-
methylbenzimidazoline (12) with transition metal salts (copper(I) iodide or bis(triphenylphosphine)nickel(II)
chloride) in acetonitrile. X-ray structural analysis results for complexes 11 and 13 are presented in [25].
Scheme 2
Me
Me
N
N
CuI
Cu
I
MeCN, 82°C
Me
N
N
6
7%
N
CN
Me
Me
1
3
N
Me
Me
Me
Cl
Ni
Cl
N
N
1
2
NiCl (PPh )
2
3 2
MeCN, 82°C
N
N
1
00%
Me
Me
1
4
The potassium complex 16 was obtained by interaction of the hydroxyphenyl-substituted salt 15a with
potassium tert-butoxide in toluene. According to the method described in paper [26], the chelate carbene
complex 17a (Scheme 3) was formed in the reaction of the compound obtained with nickel perchlorate
(
dimethyl formamide complex, 1:4-1:5). The X-ray data for structure 17a are given in papers [26, 27].
Scheme 3
1-Ad
N
N
(R = 1-Ad)
t-BuOK
Ph
K
O
Ni(ClO4)2
MeCN
N
PhMe
R
+
R
R
N
N
X
N
N
N N
16
Ph
N
M
Ph
Ph
N
N
OH
OO
t-Bu
t-Bu
1
5a,b
R = t-Bu)
Br
1
7a,b
N
N
N
N
(
Pd
Br
Pd(OAc)2
Ph
N
Na CO
2 3
Ph
N
THF
DMSO
MeOH
20°C
62%
OH HO
6
5°C
18
15, 17 a R = 1-Ad, M = Ni; b R = t-Bu, M = Pd
1
553

By heating salt 15b with palladium acetate the palladium bistriazolylidene complex of 18 was formed,
which was further dehydrobrominated in situ for chelation, following the method described in [28] (Schemes 2,
3
), to give the chelate complex 17b.
The biscarbene complex 20 (Scheme 4) was synthesized by the reaction of the corresponding stable
,2,4-triazol-5-ylidene 19 [29] with palladium chloride in acetonitrile.
1
Scheme 4
t-Bu
t-Bu t-Bu
N
N
N
N
Cl
Pd
Cl
N N
:
Ph
Ph
Ph
N
N
N
PdCl2
MeCN–THF
2
1
0°C
00%
Br
Br
Br
1
9
20
The polymeric complex 22 (Scheme 5) was obtained by the reaction of the crown-salt – 1,1',3,3'-bis(3-oxa-
,5-pentylene)bisbenzimidazolium acetylacetonate (21) with copper(I) iodide.
1
Scheme 5
O
O
Me
Me
+
N
N
O
O
I
O
N
N
N
N
N
CuI
MeCN, 20°C
Cu
O
+
N
O
O
n
22
Me
Me
21
1
The specific signal of the benzyl СН protons (5.76 ppm) was observed in the H NMR spectrum of
2
1
3
complex 11 in CDCl . In the С NMR spectrum the signal of methylene carbon atom appears at 51.2 ppm,
while the signal of C-2 carbenoid carbon atom appears at 188.6 ppm. In the H NMR spectrum of the complex
3 in DMSO-d , a characteristic signal of methyl groups protons is observed (4.06 ppm), and in the С NMR
6
3
1
1
3
1
spectrum, signals of methyl group carbon atoms (34.3 ppm) and C-2 carbenoid carbon atom (190.7 ppm) are
1
observed. In the H NMR spectrum of the nickel complex 14 in a mixture of DMSO-d and Py-d , a
6
5
characteristic signal of the methyl group protons is observed at 4.47, which is slightly shifted downfield
1
3
relatively to the same signal for the complex 13, and in the С NMR spectrum, the methyl group carbon signals
1
(
35.7 ppm) and carbenoid carbon signal (180.6 ppm) are observed. For the chelate complex 17b in the H NMR
spectrum in CDCl , a singlet signal of the tert-butyl methyl protons is observed (1.60 ppm), whereas specific
3
1
3
signals in the С NMR spectrum are those of the (CH ) C group carbon atoms (30.8 and 62.6 ppm), C-3 triazole
3
3
carbon atom (153.0 ppm), C–О bond carbon atom (161.7 ppm) and C-2 carbenoid carbon atom (171.1 ppm). In
1
3
the С NMR spectrum of the corresponding palladium complex 20 in DMSO-d , the carbenoid carbon atom
6
signal is downfield shifted (171.0 ppm) relatively to the same signal of the nickel complex 14, but nearly
coincide with the signal from chelate palladium complex 17b.
1
554

1
In the H NMR spectrum of the macrocycle carbene complex 22 in DMSO-d
6
, the bridging fragment
CH O methylene groups signals (3.82 ppm) and CH N groups signals (4.30–4.70 ppm) are observed. Due to the
2
2
1
3
low solubility of this complex the С NMR spectrum measurement was performed in a solid state, and
characteristic signals of the aliphatic fragments CH O and CH N carbon atoms were observed (48.3 and 69.4
2
2
ppm, respectively) as well as the C-2 carbenoid carbon atoms signals (154.8, 164.9 ppm). Molecular mass of the
polymer 22 was determined by LC (see Experimental) as at average equal to 77 monomer units (М 43700;
w
M 42400 (M /M = 1.03)).
n
w
n
Catalytic efficiency of the obtained complexes in a ketone reduction reaction was studied to compare
their catalytic properties. Reduction of 4-biphenyl phenyl ketone (23) and benzophenone 24 (Scheme 6)
carbonyl groups was carried out in boiling 2-propanol in the presence of potassium hydroxide (50–100 mol%),
using catalysts listed in the Table 1. Main experimental results for reduction of the ketones 23, 24 are presented
in the Table 1.
Scheme 6
O
OH
cat., KOH
-PrOH
2°C
2
8
R
R
2
3, 24
25, 26
2
3, 25 R = Ph; 24, 26 R = H
TABLE 1. Catalytic Efficiency of Synthesized Azolium Salts*
Expt.
No.
Amount of
catalyst, mol%
–
1
Catalyst
Substrate
Yield, %
Time, h
TON
TOF, h
2
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
*
—
—
23
23
23
23
23
23
23
23
23
23
23
23
23
23
23
23
23
23
23
24
24
23
23
—
—
3
65
29
56
97
96
96
100
56
75
75
65
53
98
45
70
100
50
85
55
80
76
78
16
13
13
13
13
3
—
—
—
—
2
2
*
*
10
10
2.8
0.2
10
10
100
10
0.56
9.7
0.04
0.8
11
0.1
960
320
320
333
160
17а
17b
14
0.1
3
960
0.1
3
1000
560
0.1
3.5
0.25
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
20
0.1
750
3000
188
CuCl
CuІ
11
0.1
750
0.1
6
650
108
0.01
0.01
0.01
0.01
0.01
0.001
0.001
0.001
0.001
1
6
2
5300
9800
4500
7000
10000
50000
85000
55000
80000
76
883
13
4900
1500
3500
5000
17а
17b
22
3
2
2
13
2.5
3
20000
28330
18330
32000
9.5
22
13
3
22
CuCl
CuCl
2.5
8
10
8
7.8
1
_
*
*
______
10 ml of 0.1 M KOH solution in 2-propanol per 1 mmol of substrate were used.
2
Equivalent amount of potassium 2-propoxide was used instead of
potassium hydroxide.
1
555

As it can be seen from the data in Table 1, using of potassium 2-propoxide was rather inefficient (Exp. No.
), and noticeable better results were obtained with the use of potassium hydroxide (Exp. No. 2). Azolium
1
alkoxide, generated from the salt 10, has insignificant catalytic effect on the ketone 23 reduction (Exp. No. 3–5).
Yields of the carbinol 25 were increased in experiments with 2-propoxide and potassium hydroxide using
1
0 mol% of the catalyst. Maximum yield of the carbinol 25 using potassium 2-propoxide was obtained only in
case of the salt 10 amount of 100 mol% and was equal to 56 % (Exp. No. 4). Thus, potassium 2-propoxide was
in all cases less effective than potassium hydroxide.
Catalytic efficiency of the metal carbene complexes is much higher than of the benzimidazolium salt 10.
Comparison of TON and TOF for the catalysts 11, 14, 17а,b, 20 at concentrations of 0.1 mol% showed that
efficiency of the nickel complex 14 is noticeably lower than that of the copper complex 11 and the nickel and
palladium chelate complexes 17а,b (compound 14 was partially decomposed with formation of a metallic nickel
in the course of reaction). Palladium complex 20 efficiently catalyzes the reaction during first minutes of the
process. A complete catalyst deactivation occurred at approximately 75% conversion.
For highly catalytically effective compounds 11, 17а,b, 22, it was possible to perform a comparison of
the TON and TOF values at a lower concentration (0.01 mol%). For the monocarbene complex 11 and chelate
complexes 17a,b the indexes TON and TOF were close, but the most effective was the palladium chelate
complex 17b. copper(1) biscarbene complex 13 and the polymeric carbene complex 22 were even more
effective .
TON and TOF values are maximum for compounds 13 and 22 at concentrations of 0.001 mol%, whereas for
the polymeric catalyst 22 (Exp. No. 19) these values are slightly higher than for the complex 13 (Exp. No. 18). For
the most active rhodium(III) carbene complex 9 they were noticeably increased in both cases in reaction with the
–
1
related benzophenone (TON 10580, TOF 441 h ). TON value for the complex 9 is lower than that for
compounds 13, 22, but the difference in TOF values is especially high due to the long reaction time using the
known catalyst 9 (up to 24 h) with yields not higher than 86%. Almost quantitative yields of the compound 25
(
Exp. No. 14, 17) were observed in case of catalysis with complexes 13, 22 during 2 hour of the reaction time.
Benzophenone 24 at the catalyst concentration of 0.001 mol% was reduced analogously with formation
of benzhydrol 26 with high TON and TOF values comparable with those for the ketone 23 reaction.
It should be noted that the inorganic copper halogenides (CuCl, CuI) are considerably less active than
their heterocyclic carbene complexes. Reaction completion in these cases could not be reached even using
10 mol% catalyst concentrations.
The probable mechanisms of the ketone catalytic reduction with 2-propanol in the presence of potassium
hydroxide are presented below (Scheme 7).
Mechanism of the reduction of carbonyl compounds with alcohols catalyzed by metal carbene
complexes is evidently similar to the effect of aluminum isopropoxide in the Meerwein-Ponndorf-Verley
reaction. Moreover, for the carbene complexes, first a halogen ion exchange for an alkoxide ion probably happens,
whereas the alkoxide ion is formed in equilibrium from potassium hydroxide and isopropanol (Equation 1), with
formation of a metal complex alkoxide (Equation 2). Further, analogously to the Meerwein-Ponndorf-Verley
reduction, an interaction of the carbonyl compound with the vacant d-orbital of the metal and a hydride transfer
from alcoholate group to the carbonyl carbon atom in a cyclic transition state occurs (Equation 3).
Similarly, in chelate complexes 17a,b, a displacement of phenolate ion from the metal coordination sphere
with subsequent restoration of the chelate structure and acetone formation may occur. However, another way is also
possible, proposed earlier in [31], where a metal hydride acts as an intermediate (Equation 4), which reduces the
multiple carbonyl bond (Equation 5). This reaction direction was confirmed by transition metal hydrides
isolation in some cases [3].
1
556

Scheme 7
KOH + 2-PrOH
2-PrOK + H O
(1)
(2)
2
ML X + 2-PrOK
ML Xm-1O-Pr-2 + KX
n
m
n
1
Ar
Me
1
Ar
H
1
Ar
Ar
Me 2-PrOH, X–
Ar
Ar + ML X
ML Xm-1O-Pr-2
n
n m
(
3)
4)
O
O
– 2-PrO–
O
OH
+ Me CO
2
M
LnX
m-1
Me
Me
H
H
(
O
M L X
n m–1
–
Me CO
2
LnXm–1
M
1
1
Ar
Ar
H
2-PrOH Ar
2-PrO–
Ar
+
+ ML X
n m
M
(5)
–
OH
O
LnX
m–1
L - carbene ligand, X other ligands (e.g., halide, etc)
Thus three classes of catalysts of the hydride transfer from 2-propanol to ketones have been found –
carbene complexes of copper(I), nickel, and palladium, and also carbenes, which are, however, less effective. It
is essential that copper (I) complexes are substantially more effective than the known rhodium, iridium and
ruthenium complexes. The most effective catalyst proved to be the copper(I) carbene polymeric complex.
Copper(I) biscarbene monomeric complex was of the similar efficiency.
EXPERIMENTAL
1
13
H and C NMR spectra were recorded on Gemini 200 and Bruker Avance II 400 spectrometers with
TMS as internal standard. Purity of substances was monitored by TLC on Silufol plates with a 10:1 CHCl –MeOH
3
mixture.
Molecular properties of polymer 22 were studied on the measurement complex for Du Pont liquid
chromatography, fitted with bimodal Zorbax PSM-100 and 1000 columns, each of which can be linearly
2
6
calibrated in molecular mass from 10 -10 . Chromatograph was calibrated using Du Pont PS polysterene standard
with molecular masses of M 1000, 50000 and M /М = 1.01. Oligomer coming out of the column was detected by
w
w
n
an ultraviolet detector set to 282 nm wave length. DMF purified and dried according to the standard methods was
used as eluent. Analyses temperature was 25С and the flow rate was 0.7 ml/min. System pressure was equal to 53–
55 bar. Error of the retention time detection was 1%. To determine the amount of high- and low-molecular mass
fractions, after the sample coming out from the column and signal recording using MO Spectra Physics software
program the peak area ratios were calculated for peaks which correspond to each component with certain average
molecular mass. Molecular properties of the polymer 22 were calculated using Chrom І Insoftus software program
[
32]. The method was used for molecular mass determination of polar substances, including polyelectrolites [32–
5]. Elemental analysis for metal content was carried out along with carbon, hydrogen and halogen contents
measurement using dry oxides residue after sample combustion.
1,3-Dibenzylbenzimidazol-2-ylidene)copper(I) Chloride (11). A mixture of 1,3-dibenzylbenzimida-
zolium chloride (10) (1.0 g, 3.0 mmol) and copper(I) chloride (0.3 g, 3.0 mmol) was dissolved in dry MeCN
3
(
(
15 ml), Et N (0.5 ml, 3.6 mmol) was added, and the mixture was boiled for 2 h. Then more Et N (0.5 ml,
3 3
3
.6 mmol) was added, and refluxing was continued for 30 min. The reaction product was precipitated with
water, filtered off, washed with a 1:3 2-PrOH–petroleum ether mixture, and dried over KOH. Product 11 (1.05
557
1

1
g, 84%) was recrystallized from MeCN. Yield 0.7 g (56%); mp 175-177°C. H NMR spectrum (200 MHz,
1
3
CDCl ), δ, ppm: 5.76 (4H, s, 2CH N), 7.24-7.54 (14H, m, H Ar). C NMR spectrum (50 MHz, CDCl ), δ, ppm:
3
2
3
5
1.2 (CH N); 111.8, 123.4, 127.3, 127.7, 128.5 (C Ar); 133.4, 136.3 (i-C Ar); 188.6 (C-2). Found, %: C 63.61;
2
H 4.64; Cl 8.59; Cu 15.92; N 7.24. C H ClCuN . Calculated, %: C 63.47; H 4.57; Cl 8.92; Cu 15.99; N 7.05.
2
1
18
2
Bis(1,3-dimethylbenzimidazol-2-ylidene)copper(I) Iodide (13). A mixture of 2-cyanomethyl-1,3-di-
methyl-2H-benzimidazoline (12) (2.55g, 13.6 mmol) and copper(I) iodide (1.30 g, 6.8 mmol) in MeCN (5 ml)
was refluxed for 2 h. The precipitate was filtered off, washed with a small amount of MeCN, and dried. Yield
1
2
7
.20 g (67%); mp. 220-221°C (MeCN). H NMR spectrum (200 MHz, DMSO-d ), δ, ppm: 4.06 (12H, s, 4CH );
6
3
1
3
.40 (4H, m, H Ar); 7.65 (4H, m, H Ar). C NMR spectrum (50 MHz, DMSO-d ), δ, ppm: 34.3 (CH ); 110.9
6
3
(
C-4,7); 123.0 (C-5,6); 134.0 (i-C Ar); 190.7 (C-2). Found, %: C 44.53; H 4.14; Cu 13.38; I 26.51; N 11.44.
C H CuIN . Calculated, %: C 44.78; H 4.18; Cu 13.16; I 26.28; N 11.60.
1
8
20
4
Bis(1,3-dimethylbenzimidazol-2-ylidene)nickel Dichloride (14). 2-Cyanomethyl-1,3-dimethyl-2H-benz-
imidazoline (12) (0.95 g, 5.08 mmol) in MeCN (6 ml) was added to a suspension of NiCl (PPh ) (1.66 g, 2.54
2
3 2
mmol) in MeCN (4 ml) and the mixture was refluxed for 2 h. The precipitate was filtered off, washed with ether,
1
and dried. Yield 1.07 g (100%); mp 275-278°C (MeCN). H NMR spectrum (200 MHz, DMSO-d +Py-d ) δ, ppm:
4
6
5 ,
1
3
.47 (12H, s, 4CH ), 7.30-7.78 (8H, m, H Ar). C NMR spectrum (200 MHz, DMSO-d +Py-d ) δ, ppm: 35.7
3 6 5 ,
(
CH ); 110.4, 123.8 (C Ar); 134.9, 144.2 (i-C Ar); 180.6 (C-2). Found, %: C 51.35; H 4.76; Cl 16.67; N 13.15;
3
Ni 14.07. C H Cl N Ni. Calculated, %: C 51.23; H 4.78; Cl 16.80; N 13.28; Ni 13.91.
1
8
20
2
4
Bis-(1-tert-butyl-2-(2-oxidophenyl)-3-phenyl-1,2,4-triazol-5-ylidene)palladium (17b). The salt 15b
(
(
0.23 g, 0.62 mmol) and Pd(OAc) (0.07 g, 0.31 mmol) were dissolved in a mixture of THF (10 ml) and DMSO
2
0.5 ml), heated at 50°C and stirred for 2 h. MeOH (10 ml) and Na CO (0.26 g, 2.48 mmol) were added and the
2
3
mixture stirred for 1 h. The reaction mixture was poured into water (50 ml). The precipitate was filtered off and
dried. The precipitate was dissolved in CH Cl (10 ml) and filtered through a thin layer of silica gel. The
2
2
1
solution was evaporated to dryness. Yield 0.13 g (62%); mp 140°C (PhMe). H NMR spectrum (200 MHz,
CDCl ), δ, ppm: 1.60 (18H, s, 2(CH ) C); 7.31-7.56 (18H, m, H Ar). C NMR spectrum (100 MHz, CDCl ), δ,
1
3
3
3 3
3
ppm: 30.8 (CH ); 62.6 ((CH ) C); 114.6, 121.4, 124.4, 128.5, 128.6, 129.4, 130.2 (C Ar); 126.9 (i-C Ph); 148.2
3
3 3
(i-C 2-oxydophenyl); 153.0 (C-3); 161.7 (C–O); 171.1 (C-2). Found, %: C 62.72; H 5.07; N 12.39; Pd 15.24.
C H N O Pd. Calculated, %: C 62.56; H 5.25; N 12.16; Pd 15.40.
3
6
36
6
2
Bis[4-(4-bromophenyl)-1-tert-butyl-3-phenyl-1,2,4-triazol-5-ylidene]palladium Dichloride (20).
(4-Bromophenyl)-1-tert-butyl-3-phenyl-1,2,4-triazol-5-ylidene (19) [29] (0.20 g, 0.56 mmol) in THF (1 ml)
4
was added to a suspension of palladium chloride (0.05 g, 0.28 mmol) in MeCN (1 ml) and stirred for 30 min.
The precipitate was filtered off and dried to give compound 20 (0.15 g); a further 0.1 g of complex 20 was
obtained from the mother liquor by evaporation. Overall yield 0.25 g (100%); mp 160-163°C (MeCN, subl.).
1
H NMR spectrum (200 MHz, DMSO-d
6
), δ, ppm: 1.64 (18H, s, 2(CH
3 3
) C); 7.26-7.67 (18H, m, H Ar).
1
3
6
C NMR spectrum (50 MHz, DMSO-d ), δ, ppm: 30.1 (CH ); 62.9 ((CH C); 127.8, 128.6, 128.7, 129.1, 130.4,
3
3 3
)
131.6, 132.4, 132.9 (C Ar); 143.2 (i-C Ar); 151.4 (C-3); 171.0 (C-2). Found, %: C 48.61; H 3.96; Br 18.26; Cl
8
.05; N 9.37; Pd 11.75. C H Br Cl N Pd. Calculated, %: C 48.59; H 4.08; Br 17.96; Cl 7.97; N 9.44; Pd 11.96.
3
6
36
2
2
6
Polymer of 1,1',3,3'-Bis(3-oxa-1,5-pentylene)bis(benzimidazole-2-ylidene)copper(I) Iodide (22).
Copper(I) iodide (0.66 g, 3.4 mmol) in absolute MeCN (15 ml) was added dropwise with constant stirring in an
atmosphere of nitrogen at room temperature to a solution of 1,1',3,3'-bis(3-oxa-1,5-pentylene)bisbenzimida-
zolinium diacetylacetonate (21) [30] (2.00 g, 3.4 mmol) in absolute MeCN (30 ml). The reaction product began
to crystallize from the solution. After addition of all of the copper(I) iodide, the mixture was kept at room
temperature for 40 min. The precipitate was filtered off and washed on the filter with ether in an atmosphere of
1
nitrogen. The crystals of complex were greenish in appearance. Yield 1.60 g (82%); mp 164-165°C. H NMR
spectrum (400 MHz, DMSO-d ), δ, ppm: 3.82 (8H, s, 4CH O); 4.30-4.70 (8H, m, 4CH N); 6.60-7.95 (8H, m,
6
2
2
1
3
H Ar). C NMR spectrum (100 MHz, in solid state), δ, ppm: 48.3 (CH O); 69.4 (CH N); 112.0, 123.9, 130.5,
2
2
1
34.0 (C Ar); 142.8 (i-C Ar); 154.8, 164.9 (C-2). LC: M 43700; M 42400 (M /M =1.03). Found, %: C 46.89;
w n w n
H 4.31; Cu 11.34; I 22.42; N 9.44. C H CuIN O . Calculated, %: C 46.61; H 4.27; Cu 11.21; I 22.39; N 9.88.
2
2
24
4
2
1
558

General Method for the Reduction of Compounds 23, 24 and Control of the Reaction of. 0.1 M
KOH solution (10 mmol) in 2-PrOH and a small amount of a catalyst (Table 1) were added to ketone 23 or 24
(
2 mmol). The reaction mixture was refluxed and monitored by TLC. Quantitative analysis of the starting
material and the reduction product during the reaction time was carried out as follows: 2-PrOH was evaporated
until crystallization of the remaining starting material began (a volume of about 3 ml), cooled, and the residue
was filtered off. Because of the very low solubility of the ketone in alkaline solution, the ketone did not remain
in the mother liquor (TLC monitoring). Water (12 ml) was added to the mother liquor, and the precipitate of the
carbinol 25 or 26 was filtered off, dried, and the yield of product determined. Estimation of the purity of the
1
compound isolated was determined TLC and H NMR spectroscopy.
This work was carried out with financial support of the State Fund of Fundamental Investigation of the
Ministry of Education and Sciece of Ukraine (grant No: F28.003), Ukraine National Academy of Sciences (grant
2
4.03.10), and the Russian Foundation for Fundamental Investigations (grant 10.0390418-Ukr_a).
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