New catalyst for homocoupling of aryl halides based on nickel complexes with diazabutadiene ligands

Full text of DOI:10.1134/S1070428011110236

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 11, pp. 1774−1776. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.N. Valaeva, A.F. Asachenko, P.S. Kulyabin, V.R. Flid, A.Z. Voskoboinikov, 2011, published in Zhurnal Organicheskoi Khimii, 2011,
Vol. 47, No. 11, pp. 1734−1736.
SHORT
COMMUNICATIONS
New Catalyst for Homocoupling of Aryl Halides Based
on Nickel Complexes with Diazabutadiene Ligands
V. N. Valaevaa,b, A. F. Asachenkoa, P. S. Kulyabina, V. R. Flidb, and A. Z. Voskoboinikova
aLomonosov Moscow State University, Moscow, Russia
bLomonosov State Academy of Fine Chemical Technology, Moscow, 119571 Russia
e-mail: valaeva@gmail.com
Received June 3, 2011
DOI: 10.1134/S1070428011110236
Symmetric biaryls are commonly prepared by homo-
coupling of aryl halides. Nickel catalysts of this reaction
are especially attractive due to their availability, ease in
handling, and tolerance toward many functional groups.
Nowadays many procedures of homocoupling were
developed utilizing nickel [1, 2], but the most general
was the method first introduced in [3]. In this method
NiCl2(PPh3)2 is used where Ni(II) is reduced to Ni(0) with
the help of zinc in the presence of Et4NI, but the procedure
is not free of disadvantages: The necessity to use large
amounts of the catalyst (10–50 mol%) and of relatively
expensive and toxic ligand; the products often form in
a low yield, are difficult to separate by chromatography
from triphenylphosphine. Therefore we searched for the
other, more efficient and available catalytic systems.
At the first stage of the research we synthesized diaz-
abutadiene ligands containing diverse substituents both
at the nitrogen and carbon atoms of the diazabutadiene
frame, and then the capability of nickel complexes with
these ligands was studied to catalyze the bromobenzene
homocoupling in the presence of activated zinc (reducer)
and salt additive (Et4NI).
N
N
N
N
Ia
Ib
As known, in the homocoupling are used not only
complexes with phosphine ligands, but also with bipyridyl
ligands [1, 2, 4–7]. We found besides that the catalyst
based on о-phenanthroline also exhibited a moderate
activity in homocoupling of bromobenzene. Therefore we
concluded that in this reaction complexes of nickel with
easily available diazabutadiene ligands might be used.
Thiese complexes were formerly used for preparation
of difficultly available ethylene copolymers with polar
monomers [8–10].
N
N
N
N
Ph Ph
Ic
Id
N
N
R1
R1
N
N
R1
R1
R2
R2
Ie
1774

NEW CATALYST FOR HOMOCOUPLING OF ARYL HALIDES
1775
Number of catalytic cycles (TOF) in bromobenzene homocou-
pling for nickel catalysts containing various diazabutadiene
ligands
The efficiency of the catalytic systems was estimated
by the number of catalytic cycles in a time unit in the
bromobenzene homocoupling. The results of this study
presented in the table show that among the compounds
investigated ligands Ib, Ie provide the most active
catalysts of the bromobenzene homocoupling. The nickel
complexes with the other diazabutadiene ligands are far
less active in the reaction under study. The activity of the
traditional Iyoda catalyst based on triphenylphosphine is
essentially lower (more than 50 times) than the activity
of the catalyst with ligand Ib.
Ligand
TOF, s–1
Iа
Ib
Ic
Id
Ie
0.0009
0.82
0.13
0.003
0.78
PPh3 (10 mol%)
0.03
It should be noted that besides the high activity the
developed catalytic system possesses also the other ad-
vantages: the accessability of nontoxic diazabutadiene
ligands and the possibility to perform the homocoupling
in the presence of only 1 mol% of catalyst (against
10–50 mol% necessary in procedure [3]). The serious
disadvantage of the triphenylphosphine is its difficult
separation from the biaryls by means of column chro-
matography; this difficulty is not met with the studied
diazabutadiene ligands. The other drawback at the use
of the triphenylphosphine is the migration of the phenyl
fragment from the phosphorus atom to nickel resulting
in the formation of unsymmetrical side products [1, 2].
It turned out that the diazabutadiene ligands did not enter
into any side reactions.
halides including sterically loaded substrates.
Homocoupling of aryl halides. General procedure.
Underinertatmosphereto49mg(0.75mmol)ofactivated
zinc (preliminary washed with 2% hydrochloric acid,
water, ethanol, and ether and dried in a vacuum) was
added 125 mg (0.5 mmol) of Et4NI, 15 mg (0.05 mmol) of
NiBr2·dimethoxyethane, 0.05 mmol of diazabutadiene
ligand, 5 ml (1 mmol) of 0.2 M arylhalide solution in
THF. The reaction mixture was stirred at 70°С over
10 h, the target product was isolated from the reaction
mixture by column chromatography on silica gel 60А
(40–60 μm).
N-[(1E,2E)-2-(2,6-Dimethylphenyl)ethylidene]-
2,6-dimethylphenylamine (Ia). To a solution of 1.21 g
(10 mmol) of 2,6-dimethylphenylamine in 100 ml of
ethanol at 25°C was added 0.72 g (5 mmol) of 40%
aqueous glyoxal. The mixture was stirred for 16 h at
25°C. The separated precipitate was filtered off and
dried in a vacuum. Yield 2.13 g (85%), mp 154–155°С.
1Н NMR spectrum (CDCl3), δ, ppm: 2.19 s (12H, о-CH3),
6.93 t (2H, p-CH, J 7.6 Hz), 7.07 d (4H, m-CH, J 7.6 Hz),
8.13 s (2H, HC=N). 13С (CDCl3), δ, ppm: 18.20, 125.5,
126.5, 128.9 (о-CH3), 148.4 (aryl), 163.2 (HC=N). Found,
%: C 81.70; H 7.72; N 9.89. C18H20N2. Calculated, %:
C 81.78; H 7.63; N 10.60.
The investigation of the applicability range of new
catalysts for the synthesis of substituted symmetric bi-
phenyls from substituted aryl bromides (see the scheme)
showed that the homocoupling products formed in virtu-
ally quantitative yield from substrates containing both
dondor and acceptor substituents in the benzene ring.
Biaryls IIа–IIf were obtained in yields of 99, 97, 95, 99,
92, 94% respectively.
Br
.
NiBr2 dimethoxyethane,
ligand
2
Zn, Et4NI, THF, 70°C
N-[(1E,2E)-2-(2,6-Diisopropylphenyl)ethylidene]-
2,6-diisopropylphenylamine (Ib). To a solution of 100 g
(0.56 mol) of 2,6-diisopropylphenylamine in 500 ml of
ethanol at 25°C was added 31.5 ml (0.28 mol) of 40%
aqueous glyoxal and several drops of formic acid. The
mixture was stirred for 3 h at 25°C. The separated yel-
low precipitate was filtered off, washed with 100 ml of
methanol, and dried in a vacuum. Yield 81.74 g (78%),
yellow crystals. 1Н NMR spectrum (CDCl3), δ, ppm:
1.28 d (24H, CHMе2, J 7.6 Hz), 3.03 septet (4H, CHMе2,
J 6.4 Hz), 7.27 m (6H, C6H3, J 7.6 Hz), 8.19 s (2H,
R
R
R
IIа_IIf
R = 3,5-Me (a), 4-MeO (b), 2-MeO (c), 4-COOMe (d), 4-F
(e), 4-CF3 (f).
Thus we studied new highly active nickel catalyst
based on diazabutadiene ligands for homocoupling of aryl
bromides. We plan further to obtain the other substituted
diazabutadienes, to investigate nickel catalyst underlain
by them, and also further study the applicability range
of this reaction for diverse substituted aryl and hetaryl
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 11 2011

VALAEVA et al.
1776
HC=N). Found, %: C 83.14; H 9.77; N 7.31. C26H36N2.
Calculated, %: C 82.93; H 9.64; N 7.42.
1Н NMR spectrum (CDCl3), δ, ppm: 0.97 d (12H CH3,
J 6.9 Hz), 1.24 d (12H, CH3, J 6.9 Hz), 3.04 heptet (4H,
CH, J 6.8 Hz), 6.64 d (2H, Ar, J 7.2 Hz), 7.31–7.20 m
(6H, naphthyl), 7.36 d.d (2H, Ar, J 8.1, 7.2 Hz), 7.87 d
(2H, Ar, J 8.1 Hz). Found, %: C 86.43; H 8.14; N 5.45.
C36H40N2. Calculated, %: C 86.35; H 8.05; N 5.59.
1Н, 13С NMR spectra were registered on a spectrom-
eter Bruker Avance 400 DPX at operating frequencies
400 and 100 MHz respectively. Chemical shifts are re-
ported with respect to TMS signal. Elemental analyses
were carried out on a CHN-О-Rapid analyzer (Heraсus).
N-[(1E,2E)-2-(2,6-Diisopropylphenyl)methyl-
propylidene]-2,6-diisopropylphenylamine (Ic). To
asolutionof100g(0.56mol)of2,6-diisopropylphenylamine
in 500 ml of ethanol at 25°C was added a mixture of
24.08 ml (0.28 mol) of diacetyl and several drops of for-
mic acid. The mixture was stirred for 48 h at 25°C. The
separated yellow precipitate was filtered off, washed with
100 ml of methanol, and dried in a vacuum. Yield 89.50 g
1
(79%) yellow crystals. Н NMR spectrum (CDCl3), δ,
ppm: 1.27 d (24H, CH3, J 7.7 Hz), 2.07 s (6Н, CH3),
3.02 septet (4H, CH, J 6.3 Hz), 7.25 m (6H, Ar). Found,
%: C 83.27; H 10.05; N 6.84. C28H40N2. Calculated, %:
C 83.11; H 9.96; N 6.92.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 11 2011