Electroreductive coupling of organic halides with aldehydes catalyzed by nickel(0) complex with 2,2′-bipyridine

Article abstract of DOI:10.1023/A:1012381707114

A method of electrosynthesis of secondary alcohols from aldehydes and organic halides under the action of nickel(0) complexes is proposed. The key stage is addition of σ-complex RNi(I)bipy (bipy is 2,2′-bipyridine) to the aldehyde group.

Full text of DOI:10.1023/A:1012381707114

Russian Journal of General Chemistry, Vol. 71, No. 3, 2001, pp. 453 456. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 3, 2001,
pp. 490 493.
Original Russian Text Copyright
2001 by Budnikova, Keshner, Kargin.
Electroreductive Coupling of Organic Halides
with Aldehydes Catalyzed by Nickel(0) Complex
with 2,2 -Bipyridine
Yu. G. Budnikova, T. D. Keshner, and Yu. M. Kargin
Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center,
Russian Academy of Sciences Kazan State University, Kazan, Tatarstan, Russia
Received July 13, 1999
Abstract A method of electrosynthesis of secondary alcohols from aldehydes and organic halides under
the action of nickel(0) complexes is proposed. The key stage is addition of -complex RNi(I)bipy (bipy is
2,2 -bipyridine) to the aldehyde group.
Present-day organic chemistry strives to combine
the search for new reactions with the optimization of
known and new methods of syntheses. Economic as
well as enviromental considerations make the investi-
gators to raise the selectivity of reactions and use
more simple experimental conditions. It is for these
reasons that homogeneous catalysis is coming into
ever increasing use, since it has marked advantages,
especially from the viewpoint of selectivity and ef-
ficiency. As a matter of fact, transition metal com-
plexes in lower oxidation states, such as electro-
chemically generated Ni(0, I), Pd(0), or Co(I), can
react with various functional groups to catalyze the
formation of the C C bond [1]. The reactions of
addition to the carbonyl bond is still studied to a
lesser extent. Two main types of the reaction are
known, namely, allylation of carbonyl compounds,
and the Reformatsky reaction [2,3]. In the first case
one must use the catalytic system PdCl2 ZnCl2 [2],
and in the latter case the reaction occcurs only with
-chloroacetates [3].
carbonyl group is -coordinated, while -coordination
is less common [6]. -Complexes are formed with
aliphatic, and -complexes with aromatic aldehydes
and ketones. For some complexes, such as rhenium(0)
ones with aromatic aldehydes, there is observed an
equilibrium between the two types of complexes [7].
The predominance of - or -character of coordination
depends on the basisity of the carbonyl group [7]. As
an example, donor groups in the aromatic ring
enhance the basic character of the carbonyl group,
while acceptor groups, on the contrary, cause a fall in
the basicity thus promoting delocalization of the
double bond in the molecule and favoring -binding.
We suggested that in the presence of organic
halides the electrochemically generated Ni(0)bipy
complexes either -complexes RNi(II)Xbipy, or the
products of oxidative addition RNi(I)bipy, would
react with carbonyl group to give the products of
reductive addition and, eventually, alcohols. Of
particular interest was investigation of the possibility
of synthesis of alcohols with electron-acceptor sub-
stituents in the aromatic ring which are impossible to
prepare by common chemical methods in one stage.
In addition, voltammetry and preparative electrolysis
make it possible for the mechanism of the reaction to
be studied by breaking the reaction up and simulating
the separate parts. Up to now the reactions of organo-
nickel compounds with carbonyl group were not
studied.
The aim of the present study was to examine the
possibility of using -organic complexes RNi(II)X
bipy (bipy is 2,2 -bipyridine) obtained by the reaction
of Ni(0) complex Ni(bipy) with organic halides for the
addition to the carbonyl group under the conditions of
electrolysis with soluble anodes.
The character of the reaction of organometallic
compounds with carbonyl derivatives depends on their
nature. Grignard reagents are able to add to the
carbonyl group to reduce it to hydroxy group. Transi-
tion metals, including Ni, Pt, and Mo in various
oxidation states, can coordinate with the carbonyl
group [4], two types, - and -coordination being
distinguished [5, 6]. In the majority of complexes the
The preliminary experiments on functionalization
of carbonyl compounds were performed in an un-
separated cell with a magnesium anode and NiBr2bipy
as a catalyst precursor. As an electrolyte we used a
solution of Bu4NBF4 in DMF with added benzal-
dehyde and 2-bromotoluene. It was found that under
1070-3632/01/7103-0453$25.00 2001 MAIK Nauka/Interperiodica

454
BUDNIKOVA et al.
Coupling of organic halides with aldehydes catalyzed by Ni(0)bipy (1 mmol NiBr2bipy, 15 mmol ArX, 7.5 mmol RCHO,
2
1
Bu4NBF4 as a background electrolyte, c 10 mol l , I 0.1 A, nickel gauze as a cathode, 20 )
Yield, %
from C6H5CHO
ArX
RCHO
Product
Anode
2-BrC6H4CH3
C6H5CHO
C6H5CH(OH)C6H4CH3-2
Mg
Zn
Ni
14 (75a)
18
61
Fe
63
80
b
2-BrC6H4CH3
2-CH3OC6H4CHO
2-CH3OC6H4CH(OH)C6H4CH3-2
Ni
60
71
b
2-BrC6H4CH3
2-BrC6H4CH3
2-BrC6H4NH2
Cyclohexanone
C8H17CHO
C6H5CHO
C6H5CHO
C6H5CHO
C6H5CHO
2-CH3C6H4C6H10(OH)-1
C8H17CH(OH)C6H4CH3-2
C6H5CH(OH)C6H4NH2-2
2-CH3OC6H4CH(OH)C6H5
C6H5CH(OH)C6H4CO2CH3-4
Ni
50
58
42
b
b
2-BrC6H4OCH3
4-ClC6H4CO2CH3
CH3C(Br)=CHCH3
Ni
85
b
50c
52
c
b
C6H5CH(OH)C(CH3)=CHCH
3
a
b
c
7 mmol NiBr bipy.
2
Stainless steel.
Yield from ArCl, 7.5 mmol RCHO.
certain conditions a product of addition to the
and only waves at more negative potentials remain.
carbonyl group, (2-methylphenyl)phenylcarbinol was Moreover, it was shown that at the potential of reduc-
formed as a result of electrosynthesis, and the yield
of the latter compound was proportional to the con-
centration of NiBr2bipy in the solution (see table and
Fig. 1). The above observation makes it possible to
suggest that nickel(II) ions are fixed in nickel(II)
alcoholate and moved out of the cycle. 2-Bromo-
toluene as a model compound was used because on
reaction with Ni(0) it forms stable organonickel com-
pounds which makes it possible for the reaction
pathway to be followed.
tion Ni(II)/Ni(0) of 1.2 V relative to a saturated
mercurous chloride electrode no alcohol is formed,
and the target coupling process takes place only at
more negative potentials corresponding to further
reduction of the -complex TolNiBr (Tol is 2-tolyl),
1.35 V (Fig. 2). The following scheme of the reac-
tion can be suggested.
Ni+2Br2bipy + 2e
Ni0bipy + 2 Br
TolNi+2Brbipy
1.2 V, (1)
(stable), (2)
(3)
Ni0bipy + TolBr
The absence of the catalytically active form of
nickel(II) after passing 2 F of electricity per mol Ni at
1.2 V is evidenced by the voltammograms of the
solution: the reduction wave of NiBr2bipy disappears,
TolNi+2Brbipy + PhCHO
TolNi+2Brbipy + e TolNi+1bipy + Br
,
1.35 V, (4)
TolNi+1bipy + PhCHO
PhCH Tol + bipy, (5)
O Ni
15.0
12.5
10.0
Anode-generated atoms of magnesium do not
substitute for nickel(II) in the forming alcoholate, and
the catalyst is thus consumed. We speculated that
replacing the anode by a nickel or a one similar with
it in properties would allow the catalyst to be con-
sumed in significantly lower amounts because of
regeneration. The results of electrosyntheses are given
in the table. It is evident that the syntheses proceed at
high yields of the alcohol with the use of nickel or
iron, as well as stainless-steel anodes, and other
aromatic aldehydes with donor groups in the ring
(CH3O) and aliphatic aldehydes and cyclohexanone
can be involved into the reaction. As arylating agents
7.5
5.0
2.5
2.5 5.0 7.5 10.0 12.5 15.0 17.5
c[Ni(II)] 102, M
Fig. 1. Plot of the concentration of the reaction product,
(2-methylphenyl)phenylcarbinol, in the electrolyte vs.
the initial concentration of NiBr bipy (Mg anode, 1.35
to 1.47 V).
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 3 2001

ELECTROREDUCTIVE COUPLING OF ORGANIC HALIDES
1.35 to 1.50 V
455
1-amino-2-bromobenzene and 2-bromo-1-methoxy-
benzene can be used which, but only those with orto-
position of the donor substituent probably provide
stability of the ArNi(I)bipy reagent. In the case of
meta- and para-substituents biaryls Ar2 are mainly
formed, and no noticeable addition to the carbonyl
bond is observed. At the same time, alcohol with an
acceptor substituent CO2Me in the ring was obtained
with reasonable yields when X = Br was changed by
X = Cl. This allowed the homocoupling reaction of
ArNi(I)bipy with ArX to be slowed down and to
direct the process to the functionalization of the
aldehyde, but in this case three- or four-fold excess of
the aldehyde is needed. The fact that aromatic al-
dehydes with acceptor substituents in the ring which
favor -binding practically do not enter the reaction
(only trace amounts of the corresponding alcohols
were found), and that the reaction does take place with
aliphatic aldehydes, is suggestive of the predominant-
ly -character of binding between organonickel
complex and the C=O group of the aldehyde.
15
10
1.2 V
5
2
4
6
8
Q, F/mol Ni(II)
Fig. 2. Plot of the yield of (2-methylphenyl)phenyl-
carbinol vs. the quantity of electricity consumed in
the process.
The reference electrode was saturated mercurous
chloride electrode placed into DMF and Bu4NBF4 and
separated from the solution by a glass barrier. For the
preparative syntheses we used a cylindrical cathode
made of nickel gauze. The process was carried out
under galvanostatic conditions at I 100 200 mA
(20 ). The experimental conditions: into 40 ml of the
solvent (DMF) 15 mmol of an organic halide ArX and
7.5 mmol of a carbonyl compound RCHO (in the case
of 4-ClC6H4O2CH3 7.5 mmol of ArX and 30 mmol
of RCHO, respectively), 1 mmol of NiBr2bipy was
added; the background electrolyte was Bu4NBF4
H
N
R C
O
R C=O
-----
Ni Ar
Ni Ar
It can be thus concluded that electroreductive
coupling of organic halides and aldehydes catalyzed
by nickel complex with 2,2 -bipyridine is an efficient
process demonstrating the potentialities of homo-
geneous electroreductive reactions.
2
1
(c 10 mol l ).
1
EXPERIMENTAL
(2-Methylphenyl)phenylcarbinol. H NMR spec-
trum (CDCl3), , pp: 2.09 s (3H), 2.43 s (1H), 5.79 s
(1H), 6.98 7.20 m (1H). 13C NMR spectrum (CDCl3),
C, ppm: 142.89, 141.48, 135.37, 130.53, 128.46,
127.54, 127.16, 126.31, 126.13, 73.29, 19.40.
The reaction products were identified by means of
1H and 13C NMR spectroscopy on a Brucker
(200 MHz) spectrometer, their concentrations in the
course of electrolysis were monitored by GLC with
the use of dodecane as an internal reference. For the
electroanalytical experiments we used an EGG-PARC
273A potentiostat with the EGG-PARC M270 soft-
ware.
1
(2-Aminophenyl)phenylcarbinol. H NMR spec-
trum (CDCl3), , ppm: 6.43 6.68 m (2H), 5.73 s (1H),
3.47 s (2H), 2.28 s (1H), 6.90 7.10 m (2H), 7.15
7.47 m (5H). 13C NMR spectrum (CDCl3), C, ppm:
128.67, 128.52, 128.42, 128.23, 127.34, 126.31,
118.09, 116.72, 74.65.
The solvent DMF (Merck, main substance content
over 99.5%) was dried over 4 molecular sieves and
used without further purification. Tetrabutyl-
ammonium fluoborate (over 99%) was dried at 70 C
in a vacuum for 24 h and then kept in a dry vessel.
The complex NiBr2bipy was prepared from NiBr2
3H2O and equivalent of 2,2 -bipyridine in ethanol; the
solution was left for 12 h, the precipitate was filtered
off, washed with ethanol, and dried at 70 C in a
vacuum for 24 h. Aryl halides and carbonyl com-
pounds were commercial products (Aldrich).
1
1-(2-Methylphenyl)cyclohexanol. H NMR spec-
trum (CDCl3), , ppm: 7.18 6.95 m (4H), 2.21 s (3H),
2.19 1.09 m (10H). 13C NMR spectrum (CDCl3),
,
C
ppm: 134.22, 130.17, 129.02, 128.40, 125.36, 40.62,
30.64, 28.85, 24.14, 23.77, 22.39, 20.02, 14.11.
1
1-(2-Methylphenyl)-1-octanol. H NMR spectrum
(CDCl3), , ppm: 7.30 7.34 m (1H), 6.95 7.10 m
(4H), 4.77 4.71 m (1H), 2.19 s (3H), 1.57 0.75 m
(17H). 13C NMR spectrum (CDCl3), C, ppm: 142.92,
134.14, 130.65, 130.04, 126.75, 126.54, 125.98,
As an anode we used a magnesium rod (Johnson
Mattey) which was polished prior to every experiment. 125.00, 119.77, 114.68, 70.44, 37.95, 31.69, 29.17,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 3 2001

456
BUDNIKOVA et al.
29.37, 29.10, 29.05, 27.51, 26.17, 25.83, 22.46, 18.81, (1H), 5.02 s (1H), 2.92 s (1H), 1.53 1.76 m (3H),
13.87.
1.45 m (3H). 13C NMR spectrum (CDCl3), C, ppm:
142.64, 142.49, 137.53, 137.27, 130.26, 128.18,
127.94, 127.20, 127.05, 126.92, 126.65, 126.11,
125.39, 121.92, 120.88, 79.02, 13.02, 11.49.
2-Methoxyphenyl(2-methylphenyl)carbinol. 1H
NMR spectrum (CDCl3), , ppm: 2.43 s (3H), 3.98 s
(3H), 6.48 s (1H), 7.04 7.44 m (8H), 7.48 7.73 m
(1H). 13C NMR spectrum (CDCl3), C, ppm: 156.81,
140.44, 135.40, 131.05, 130.63, 129.99, 128.57,
127.62, 127.00, 126.35, 125.73, 120.51, 119.74,
110.27, 67.92, 55.18, 18.98.
2-Methoxyphenyl(phenyl)methanol. 1H NMR
spectrum (CDCl3), , ppm: 7.32 6.98 m (9H), 5.95 s
(1H), 3.63 s (3H), 2.0 s (1H). 13C NMR spectrum
(CDCl3), C, ppm: 156.49, 143.40, 132.01, 131.35,
128.50, 128.01, 127.58, 126.96, 126.47, 120.65,
110.60, 71.66, 55.20.
REFERENCES
1. Nedelec, J.Y., Perichon, J., and Troupel, M., Top. Curr.
Chem., 1997, vol. 185, pp. 141 173.
2. Durandetti, S., Sibille, S., and Perichon, J., J. Org.
Chem., 1989, vol. 54, no. 9, pp. 2198 2204.
3. Conan, A., Sibille, S., and Perichon, J., J. Org. Chem.,
1991, vol. 56, no. 6, pp. 2018 2024.
4. Yo-Hsin, H. and Gladysz, J.A., J. Chem. Ed., 1988,
vol. 90, no. 4, pp. 298 303.
4-Methoxycarbonylphenyl(phenyl)carbinol. 1H
NMR spectrum (CDCl3), , ppm: 7.82 7.86 m (2H),
7.73 7.11 m (7H), 5.69 s (1H), 4.50 s (1H), 3.75 s
(1H). 13C NMR spectrum (CDCl3), C, ppm: 196.9,
167.12, 148.91, 143.26, 131.79, 129.73, 129.02,
128.61, 128.49, 127.84, 127.58, 126.99, 126.65,
126.35, 115.23, 75.77, 52.11.
5. Tsou, T.T., Huffman, J.C., and Kochi, J.K., Inorg.
Chem., 1979, vol. 18, no. 8, pp. 2311 2317.
6. Kaiser, J., Sieler, J., Walter, D., Dinjus, E., and Go-
lic, L., Acta Cryst. (B), 1982, vol. 38, no. 5, pp. 1584
1588.
7. Quiros Mendez, N., Seyler, J.W., Arif, A.M., and
Gladysz, J.A., J. Am. Chem. Soc., 1993, vol. 115, no. 6,
pp. 2323 2334.
2-Butenyl-2-methyl-1-phenyl-1-ol. 1H NMR spec-
trum (CDCl3), , ppm: 7.11 7.31 m (6H), 5.58 5.69 q
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 3 2001