Highly reactive σ-organonickel complexes in electrocatalytic processes

Article abstract of DOI:10.1016/S0022-328X(01)00813-0

The electrochemical reduction of nickel complexes with 2,2′-bipyridine in the presence of ortho-substituted organic halides or white phosphorus yields the highly reactive σ-organonickel complexes. These complexes selectively react with organic halides for

Full text of DOI:10.1016/S0022-328X(01)00813-0

Journal of Organometallic Chemistry 630 (2001) 185–192
www.elsevier.com/locate/jorganchem
Highly reactive s-organonickel complexes in electrocatalytic
processes
Yulia H. Budnikova a,*, Jacques Perichon b, Dmitry G. Yakhvarov a, Yuri M. Kargin a,
Oleg G. Sinyashin a
a Arbuzo6 Institute of Organic and Physical Chemistry, Russian Academy of Sciences, 8 Arbuzo6 St., 40088 Kazan, Russia
b Laboratoire d’Electrochimie, Catalyse et Synthe`se Organique (UMR 28), C.N.R.S.-Uni6ersite´ Paris 12 Val de Marne 2, rue Henry Dunant,
94320 Thiais, France
Received 26 January 2001; accepted 29 March 2001
Abstract
The electrochemical reduction of nickel complexes with 2,2%-bipyridine in the presence of ortho-substituted organic halides or
white phosphorus yields the highly reactive s-organonickel complexes. These complexes selectively react with organic halides
forming cross-coupling products. The mechanism of these processes was investigated using the method of cyclic voltammetry and
preparative electrolysis. The key intermediates of electrochemical functioning of white phosphorus in conditions of metallocom-
plex catalysis were detected. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Homogeneous redox catalysis; Cross-coupling; Ni(0) complexes; s-Organonickel complexes; White phosphorus; Organic halides;
Electrochemistry
1. Introduction
crucial precursors and intermediates in a number of
useful carbonꢀheteroatom bond cleavages (epoxide de-
oxygenation, dibenzothiophene desulfurization, cross-
coupling according to the Kumada reaction) [1–5]:
The elaboration of the ecologically safe and resource-
saving chemical and engineering processes is one of the
strategic directions in the development of science and
technology. In this context, homogeneous catalysis has
been increasingly used due to the valuable advantages,
involved notably in terms of selectivity and efficiency.
Electrochemistry is related to this field in many ways.
For example, the synthesis of many organometallic
compounds is performed electrochemically, with elec-
trochemistry contributing to the investigation of the
reactivity of coordination compounds and highlighting
the possible reaction mechanisms.
This communication seeks to demonstrate some
novel possibilities of obtaining highly reactive s-aryl
nickel complexes by electrochemical methods and using
them in electrocatalytical reactions yielding compounds
with various CꢀC and CꢀP bonds.
These compounds are of special interest, because
they just border on the limits of stability and as a rule
decompose on attempted isolation. The metalꢀcarbon
bond is rather reactive, and only several organonickel
s-complexes are yet described.
The application of electrochemistry allowed to make
the process of elaborating new synthetic reactions pro-
ceed via Ni complexes. The advantages of the approach
proposed for their synthesis and investigation are as
follows:
“ organonickel s-complexes are electrochemically sim-
ple to synthesize in mild conditions;
“ they enter into various reactions in situ;
“ they are intermediates in electrocatalytic reactions of
cross-coupling, transformation of olefins, aldehydes,
etc. with a Ni(0) catalyst;
Organic s-complexes of Ni are rather poorly investi-
gated compounds though they have been reported to be
* Corresponding author. Fax: +7-8432-359512.
E-mail address: yubudnik@kzn.ru (Y.H. Budnikova).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00813-0

186
Y.H. Budniko6a et al. / Journal of Organometallic Chemistry 630 (2001) 185–192
“ they are poorly known s-complexes of metals which
may, when necessary, be studied both on their own
and as model compounds to gain an insight into the
mechanisms of organometallic synthesis;
“ the possibility to exist in various oxidation states was
found for some Ni s-complexes, e.g. RNiXbipy,
RNibipy, R2NiXbipy, R2Nibipy with various
reactivities.
We proposed a novel method to transform halo-
genated organic and organoelemental compounds and
also white phosphorus with Ni(0) complexes under
conditions of electrochemical catalysis and investigated
the mechanism of the process, the nature of intermedi-
ates and the synthetic possibilities of these reactions.
Organonickel s-complexes have been found to be the
key intermediates in these transformations.
Ni(0) complexes and to estimate the reactivity of
Ni(0)bipy complexes relative to various substrates, the
stability of intermediates in the catalytic cycle.
Electroreduction of Ni(II) complexes with 2,2%-bipy
(L) occurs via three reversible successive stages of elec-
tron transfer (Fig. 1) [6–9]:
Ni(II)L3+2e X Ni(0)L2+L, EpC
1
’
Ni(0)L2+e X [Ni(0)L2]−
,
EpC
2
’
L+e X L−
,
EpC
3
The anodic component of the first wave (C1)
NiBr2bipy reduction disappeared, and two new waves
(C3 and C4) emerged at more negative potentials in the
presence of aryl bromides (Fig. 2).
The waves C3 and C4 in one form or another corre-
spond to the reduction of the products of oxidative
addition, i.e. nickel s-aryl complexes [9]. We succeeded
in determining the nature of s-aryl complexes reduced
2. Results and discussion
at the ECp and ECp potentials by methods of prepara-
tive electrolysis and cyclic voltammetry. The instability
of nickel s-phenyl complexes makes it impossible to use
them in the modelling of more complicated processes of
cross-coupling of organohalides. A s-complex from
2-Br-toluene synthesized according to reaction (2) is
sufficiently stable in solution, and can be used to study
the mechanism of cross-coupling of organic halides or
other processes.
3
4
Voltammetric behaviour of NibipynX2 (n=1–3, X=
Br, BF4) (bipy=2,2%-bipyridine) complexes with vari-
ous RX concentrations was studied to establish: the
potentials of catalytic regeneration of Ni complexes in
the presence of organohalides RX, the reduction poten-
tials of the products of the RX oxidative addition to
C
1
NiBr2bipy+2e ? Ni0bipy+2Br−
(1)
(2)
(3)
(4)
A
1
Ni0bipy+TolBr“TolNiBrbipy
stable in solution
TolNiIbipy+Br−
TolNiIIBrbipy+e
TolNiIbipy+TolBr“Tol2NiBrbipy
stable on air
The enhanced stability of ortho-substituted phenyl
complexes is attributed to steric factors, hindering the
rotation around the s-bond of Arꢀmetal and the attack
of reagents at the axial site of the complex.
The reduction of the NiBr2bipy complex in the pres-
ence of 2-Br-Tol (1:2) results in the formation of a red
s-complex TolNiBrbipy (after 2F passes through the
Fig. 1. Cyclic voltammograms for Ni(BF4)2bipy3 (10−2 M) in
DMF+Et4NBF4 (10−1 M).
electrolyte at ECp potential (Fig. 3). The C1 wave on the
1
voltammogram disappears, and only the C3 and C4
waves with the 2e total current remain.
C
The reduction of TolNiIIBrbipy at Ep (1F) results in
claret–lilac coloured Tol2NiBrbipy which was sepa-
rated and characterized by spectral methods. The iso-
lated dry complex is characterized by one reversible
3
one-electron reduction wave with ECp = −1.96 V and
4
one one-electron oxidation wave (Br−) at +0.12 V
(Fig. 4). It is assumed that the electron in the radical–
anion formed is located on the ligand, because similar
cases are cited in literature [10,11]. Radical–anion
[Tol2NiBrbipy]− is decomposed in solution, resulting
’
Fig. 2. Cyclic voltammograms for NiBr2bipy (10−2 M) in the absence
(1) and presence (2) of aryl bromides.
in Tol2:

Y.H. Budniko6a et al. / Journal of Organometallic Chemistry 630 (2001) 185–192
187
significant rate of inversion of the three unpaired elec-
trons will result in the annihilation of each other of
paramagnetic impulses at high temperatures. However
no paramagnetic signal was detected at the temperature
of liquid nitrogen. This supports the fact that the nickel
atom does not exhibit paramagnetic properties in this
s-complex. Furthermore, the reduction potential of
Tol2NiBrbipy is in a more negative region in compari-
son with the Ni(II) reduction potential. All these exper-
imental facts demonstrate that degree of nickel
oxidation in this compound cannot equal +3. There-
fore, one can assume that the organic fragments in this
complex do not carry a negative anion charge. Proba-
bly, Tol2NiBrbipy is formed according to a mechanism
different from the standard SN2 oxidative addition
which always changes the oxidation degree of the cen-
tral ion by two units and proceeds through several
transformations in the inner sphere of the initial com-
plex TolNiIbipy. Further, the degree of nickel oxidation
in the Tol2NiBrbipy complex under consideration
equals +2, and the coordination of TolꢀNi is different
from simple s-bonding.
Fig. 3. Cyclic voltammograms for NiBr2bipy (10−2 M) with 2-BrTol
(2×10−2M) before electrolysis (1); after 2e per molecule of Ni
complex (2); and 3e per molecule of Ni complex (3).
One can make some assumptions on possible nickel
coordination in this molecule. The 3d8 electronic
configuration (Ni(II)) is known to assume the nickel
coordination of 4 or 6, with the formation of either a
planar square easily inverted in a tetrahedron or a
tetrahedral bipyramid. In the first case it can be possi-
ble to assume, that Br− is in the outer sphere of
complex I. This assumption is confirmed by the pres-
ence of the oxidation wave of free Br− anions on cyclic
voltammograms. This coordination is stable in polar
solvents, e.g. in DMF, which has strong donor proper-
ties. Nickel has probably six bonds in the solid state
(without any solvent). In this case the structure of the
complex is stabilized by the formation of binuclear
structures II, connected via a halogen bridge. The struc-
ture is typical for nickel compounds.
Fig. 4. Cyclic voltammograms for Tol2NiBrbipy (10−2 M) in
DMF+Et4NBF4 (10−1 M).
C
4
’
Tol2NiBrbipy+e X [Tol2NiBrbipy]−
(5)
(6)
’
[Tol2NiBrbipy]− “Tol2+Ni0bipy+Br−
[Tol2NiBrbipy]− “Tol2Nibipy+Br−
’
“Tol2+Ni0bipy+Br
(7)
The mechanism of the formation of compound
Tol2NiBrbipy is inadequately studied. The formal oxi-
dation degree of nickel in this compound is +3. How-
ever, such deep nickel oxidation is hardly possible in
the electrolysis conditions, as this complex is formed
and reduced at higher cathode potentials in comparison
with the standard potential of the Ni(II)/Ni(III) system.
Studies of this complex by methods of spectroscopy
and elementary analysis confirm, that this individual
compound conforms to the formula Tol2NiBrbipy.
In order to determine the degree of nickel oxidation,
ESR method was used at various temperatures. Ni(III)
is known to have the 3d7 electronic configuration as-
suming the occurrence of both high-spin
The dependence of the structure of the obtained
s-organic complex Tol2NiBrbipy on the nature of the
solvent is confirmed by its different colouring. Thus, in
DMF, the colour is claret–violet, in hexane green, and
in ether dark blue.
and low-spin
states.
s-Complex MesNiIIBrbipy is more stable and can be
exposed to air for an indefinite period of time. A
reversible one-electron reduction wave C3 correspond-
ing to MesNiBrbipy, is observed on the voltammogram
Thus, owing to unpaired electrons the nickel atom is
paramagnetic in both states. These paramagnetic prop-
erties can be recorded as an ESR signal with an appro-
priate g-factor only at low temperatures, as the

188
Y.H. Budniko6a et al. / Journal of Organometallic Chemistry 630 (2001) 185–192
1
(Fig. 5) after reduction of NiBr2bipy in the presence of
mogram after 2F at ECp . This is analogous to the case
of o-Br-toluene. Oxidative addition of MesNiIbipy to
MesBr proceeds more slowly, and the attempt to obtain
Mes2NiBrbipy fails. However, the four-electron reduc-
tion of NiBr2bipy in the presence of MesBr (1:2) results
in the selective formation of the nickel dimesityl com-
MesBr (1:1) at the ECp potential (−1.55 V), after
1
passing of 2F. The reduction of MesNiBrbipy in the
presence of some excess of bipy leads to the formation
of paramagnetic particles of MesNiIbipy, i.e. this is the
nickel-centred reversible transfer of an electron.
C
plex, i.e. Mes2Nibipy, reduced at the ECp potential (Fig.
6). This complex was isolated from solution and char-
acterized by methods of spectroscopy and elemental
analysis.
4
Ni0bipy+MesBr“1 MesNiBrbipy
(8)
stable on air
C
3
’
MesNiBrbipy+e X [MesNiBrbipy]−
X MesNiIbipy+Br−
(9)
C
4
Mes2NiBrbipy+e X Mes2Nibipy+Br−
(10)
It should be noted that the availability of two methyl
groups in ortho-position decelerates not only the reac-
tion of reductive elimination, but also the reaction of
oxidative addition with the nickel s-mesityl complexes.
Further reduction of the NiBr2bipy and MesBr solution
(1:2) in DMF in a divided electrochemical cell has been
investigated. Thus, two reversible one-electron reduc-
tion waves, C3 and C4, are observed on the voltam-
The importance attached to the intermediate s-or-
ganyl complexes of nickel, produced in a multi-stage
process, depends in many cases upon their key charac-
ter, and by their ability to determine the further course
of electrochemical and chemical transformations as a
whole.
As the model o-Br-toluene is involved in all reactions
of cross-coupling and as a result of oxidative addition
forms a stable s-complex, TolNiIIBrbipy. This was used
to study the mechanism of electrocatalytic reactions.
Thus, the course of a catalytic cycle for the cross-cou-
pling process of aromatic and heteroaromatic halides
was established [12–16]. The mechanism of this process
includes the stages of oxidative Ni(0) addition to or-
ganic halide with the formation of s-complex,
Ar1NiXbipy, its reduction to Ar1NiIbipy, and the reac-
tion of the latter with another Ar2X molecule yielding
Ar1Ar2NiXbipy and the reductive elimination to the
cross-coupling product (in some cases induced by elec-
tron transfer):
Ar1X+Ar2XNi bipy, e
Fig. 5. Cyclic voltammograms for NiBr2bipy (10−2 M) with MesBr
(10−2 M) before electrolysis (1) and after 2e per molecule of Ni
complex (2). Ni2+:MesBr=1:1.
II
“
Ar1ꢀAr2, 58–78%
The complex of NiI is always an active form of the
nickel s-complex, resulting in the target product.
Thus, the use of model nickel s-aryl complexes,
TolNiBrbipy and MesNiBrbipy, synthesized by electro-
chemical methods, allows to establish the key stage
resulting in the products of cross-coupling (ArꢀR), i.e.
the interaction of ArNiIbipy with RX and also to
estimate the value of the rate constant for this process.
These investigations allowed to expand the range of
reactions of organometallic synthesis with organonickel
s-complexes and to elaborate a convenient method for
electrosynthesis of tertiary phosphines from organic
Fig. 6. Cyclic voltammograms for NiBr2bipy (10−2 M) with MesBr
(2×10−2M) before electrolysis (1); after 2e per molecule of Ni
complex (2); and 4e per molecule of Ni complex (3). Ni2+:MesBr=
1:2.

Y.H. Budniko6a et al. / Journal of Organometallic Chemistry 630 (2001) 185–192
189
ArNiX+e“ArNiIbipy+X− (−1.65 V)
ArNibipy+Ph2PCl“ArPh2PNibipy
Table 1
Electrochemical functionalization of P4 by alkyl and aryl halides
catalysed by Ni(0)bipy {from Ni(BF4)2bipy3}
’
ArPh2PNiClbipy+e“[ArPh2PNiClbipy]−
“ArPh2P+Ni(0)+Cl−
RꢀX
PhꢀI
Anode/solvent
Zn/DMF
Products
Yield (%)
Ph3P
65
12
10
50
10
12
52
Ph2PH
PhPH2
Ph3P
Ph3PO
Ph3P
(−1.8 to −1.9 V)
Mg/DMF
Al/DMF
The proposed method of triorganyl phosphine syn-
thesis is efficient both for aromatic halides with accep-
tor and donor substituents in the ring and for
heteroaromatic halides (pyridine, thiophene, pyrimidine
and pyrazole halides). The advantages are the single-
stage character and mild conditions (room temperature)
of the process performance. Electrocatalytic cycle is
presented in the following scheme:
Ph3PO
PhꢀBr
Zn/DMF
Ph3P
50
10
9
60
15
8
30
15
31
Ph3PO
Ph2PH
(PhP)5
Ph3P
Ph3P
Ph3PO
Ph3P
Mg/DMF
Al/MeCN
Al/DMF
Ph3PO
BuꢀBr
HexꢀI
Mg/DMF
Al/MeCN
Bu3P
Bu3PO
11
55
Hex3PO
47
halides and chlorophosphines catalysed by nickel com-
plexes [17–20]. We suggested a new universal and sim-
ple method for the synthesis of unsymmetrical tertiary
phosphines in mild conditions with rather high yields
[17–20]. Some of these compounds are not easily acces-
sible and/or are expensive when obtained by usual
classical methods (including ligands for heterobinuclear
and water-soluble complexes). The method involves the
electroreduction of organic halide in the presence of
mono- or dichlorophenyl phosphine added gradually
using a Ni–bipy catalytic system in an undivided cell:
One of the problems in our investigations involves
the study of the possibility of obtaining compounds
with PꢀC bonds directly from white phosphorus and
organic halides under the action of electrochemically
generated Ni(0) complexes or organyl s-complexes,
obtained on their basis [21,22]. For this purpose, elec-
trolyses of solutions of organic halides in DMF or
acetonitrile in the presence of tetraphosphorus emulsion
and Ni–bipy complex as a catalyst were performed.
When acted upon by electrochemically generated
nickel complexes as catalysts (Table 1), it is possible to
convert white phosphorus to compounds with PꢀC
bonds, phosphines and phosphine oxides, according the
following scheme:
NiBr bipy, e
2
ArX+PhnPC3−n
“
Ar3−nPhnP,
DMF, anode−Mg, Zn
n=1,2 Yields 50−87%
P4+RXNi“(0)L ꢁPꢀR
2
-
−X
Cathode: Ni(II)L+2e X Ni(0)L, L=bipy
Anode: M−ne“Mn+ M=Mg, Zn
The product of cross-coupling with the PꢀC bond is
formed by the following substitution reaction: ArNiBr-
bipy+PhnPCl3−n“Ar3−nPhnP+NiBrClbipy (at the
initial stages of electrolysis with magnesium anode
when the reaction proceeds only at the potential of the
Ni(II)/Ni(0) system). After passing of one half of the
calculated amount of electricity through the electrolyte,
there is no initial form of the catalyst, NiBr2bipy, in the
solution, and electrolysis is carried out at larger ca-
thodic potentials (−1.8 to −1.9 V, depending on the
nature of Ar), but the product of cross-coupling is
formed even more vigorously than at the initial stages
of the electrolysis.
The interaction of organonickel compound,
RNiIIXLm, with white phosphorus was a key stage
P
Ni(0)L+RX“RNiXL“4 ꢁPꢀR+Ni(II)
It should be noted that in the absence of o-TolBr the
reaction of s-complex with P4 results only in com-
pounds of, probably, low-coordinated phosphorus,
ArPꢂNibipy:
P+ArNiBr“[ArPꢂNibipy] (lP=204 ppm).
Upon attempted isolation it proved unstable. We stud-
ied the possibility of white phosphorus interacting di-

190
Y.H. Budniko6a et al. / Journal of Organometallic Chemistry 630 (2001) 185–192
rectly with Ni(II) and Ni(0) complexes, in order to
consider other ways of formation of PꢀAr bonds.
Some theoretical approaches to the activation of
white phosphorus tetrahedron in complex formation
have been considered. The non-polar tetrahedral
molecule of P4 is characterized by weak nucleophilicity,
due to the unshared electron pairs of the phosphorus
atoms, and weak electrophilicity, caused by the lowest
unoccupied anti-bonding d orbitals. According to the
data obtained recently, P4 is liable to show itself as an
h1- or as an h2-ligand. Coordinated P4, contrary to free
phosphorus, becomes more stronger acceptor of elec-
trons and is easily reduced under the action of Ni(0)
complexes.
Consequently, such a path to the PꢀPh bond forma-
tion is competitive with the interaction of the s-aryl
complex, PhNiXbipy, with P4. Thus, white phosphorus
functionalization can be carried out by an electrochem-
ical method with formation of compounds with PꢀC
bonds under mild conditions.
It should be noted that electrochemical methods al-
low not only to carry out these processes under mild
conditions at a high rate, but in many cases also to
control them with a high selectivity.
The use of electrochemical approach to generate
Ni(0) and s-organonickel complexes appears to have
considerable promise. Firstly, it provides the possibility
to use a catalytic quantity of complex which will be
regenerated on the electrode and, in such a way, will
recycle significant amounts of various substrates. Sec-
ondly, it is possible to quantitatively estimate the rate
of catalytic reaction using an electrochemical approach,
and, in some instances, to divide the over-all process
into separate stages and to evaluate the reactivity of
intermediates and the stability of various forms of a
metal complex.
A
voltammetric study of NiBr2bipy and
Ni(BF4)2bipy3 behaviour in the presence of white phos-
phorus demonstrated that tetraphosphorus is coordi-
nated with nickel complexes, and a reduced form of the
metal yields a more stable complex than an oxidative
form. The irreversibility of the process as a whole
Ni2+(P4)bipy+2e− ? Ni0(P4)bip
may be caused by the fast subsequent chemical reaction
of P4 reduction under the action of Ni(0) complex as an
electron donor, for example
3. Experimental
Ni0(P4)bipy“Nin+(P4)n−bip
3.1. General procedures
The fast subsequent reaction leads to a shift of the
reduction curve of NiBr2bipy from the standard Nernst
potential to less negative potentials (Fig. 7). It was
found that Ni(0)bipy reacts with tetraphosphorus,
probably with the formation of binuclear complex (I),
which reacts fast with organic halides, leading to the
functionalization of cyclo-P3-fragment and formation
of mononuclear complex with Ph3P3 ligand [23]
All manipulations and reactions were carried out
under dry Ar atmosphere. All solvents employed were
purified and dried prior to use. Acetonitrile was purified
by triple fractionation distillation over phosphorus an-
hydride with the addition of KMnO4. The concentra-
tion of residual water was 10−3 M. N,N-Dimethyl-
formamide was purified according to the method in
Ref. [24], enabling to reach the residual water content
of 0.01–0.005% (weight). Supporting salts were recrys-
tallized twice: Et4NBr from MeCN, Et4NBF4 from
EtOH and were dried in vacuum at 70 °C for 2 days.
Alcohols were refluxed with BaO for 5 h and then
distilled. The white phosphorus was purified by recrys-
tallization from benzene and pyridine mixtures and
later it was washed out of absolute Me2CO and EtOH
and by ether. NiBr2bipy and Ni(BF4)2bipy3 were pre-
pared according to the method in Ref. [25]. Preparative
electrolysis at a constant current density, NMR spec-
1
troscopy of 31C, H, chromatographic analysis, elemen-
tal analysis and ESR were used for the establishment of
structure and yields of electrosynthesis products.
Cyclic voltammograms were recorded at glassy car-
bon electrode with a 1.5 mm diameter in a thermostat-
ically controlled cell in argon atmosphere. Silver
electrode Ag/AgNO3 (0.01 mol l−1 solution in MeCN)
served as a reference electrode and platinum wire served
Fig. 7. Voltammograms for NiBr2bipy (10−2 M) without (1) and
with (2) white phosphorus (10−2 M). The same solution after keeping
in argon atmosphere for 1 day (3).

Y.H. Budniko6a et al. / Journal of Organometallic Chemistry 630 (2001) 185–192
191
as an auxiliary electrode. Curve registration was per-
formed with potentiostat PI-50-1 (USSR). Scan rate
3.2.1.1. Bis-ortho-tolyl-nickel-bromide-2,2%-bipyridine.
1H-NMR (CDCl3, ppm): l 8.56–8.57 (m, 2H), 8.33–
8.37 (d, 2H), 7.79–7.82 (m, 2H), 7.28–7.31 (m, 2H),
7.10–7.14 (m, 6H, C6H4), 6.92–6.92 (m, 2H, C6H4),
1.91 (s, 6H, CH3). Anal. Found: C, 60.34; H, 5.23; Br,
16.58; N, 6.03; Ni, 12.37. Calc. for C24H22NiN2Br: C,
60.38; H, 4.61; Br, 16.77; N, 5.87; Ni, 12.37%. M.p.
(dec.) 145 °C; yield 90%.
was 50 mV s−1
.
Preparative electrolyses were performed by means of
the direct current source B5-49 in thermostatically con-
trolled cylindrical undivided electrolyser (a three-elec-
trode cell) with a 40 cm3 volume. Silver electrode
Ag/AgNO3 (0.01 mol l−1 solution in MeCN) served as
a reference electrode. Platinum with surface areas of 20
cm2 was used as a cathode. The argon flow was bub-
bled through the electrolyte in the course of electrolysis.
During electrolysis, the electrolyte was stirred with a
magnetic stirrer. The saturated solution of Et4NCl in
MeCN was used as anolyte, and the membrane was
made of paper.
Chromatographic analysis of the reaction mixtures
and synthesized compounds was carried out on a
Chrom-4 gas-liquid chromatograph using helium as a
carrier gas and a flame ionization sensor-detector. Glass
columns filled with a 5% Silicone SE-30 packing on
chromaton N-AW (0.0125–0.160) were used. NMR
spectra were registered in CDCl3 using a Varian T-60
spectrometer with the working frequency 60 MHz and
Me4Si was used as the internal standard. The 31P-NMR
spectra were recorded using a CXP-100 Bruker spec-
trometer (85% H3PO4 as an external standard) with and
without decoupling of protons. ESR signals were
recorded using the RADIOPAN (Polish electronic spec-
trometer of a X-range SE/X-2544) and calculated ac-
cording to the method in Ref. [26]; 1,1-diphenyl-2-
picrylhydrazyle (g=2.0036) was used as the external
standard.
3.2.1.2. Mesityl-nickel(II)-bromide-2,2%-bipyridine. 1H-
NMR (CDCl3, ppm): l 8.56–8.57 (m, 2H), 8.33–8.37
(d, 2H), 7.79–7.82 (m, 2H), 7.28–7.31 (m, 2H), 6.45
(m, 2H, C6H2), 2.59 (s, 6H, CH3), 2.17 (s, 3H, CH3).
Anal. Found: C, 55.03; H, 4.60; Br, 18.90; N, 6.03; Ni,
14.16. Calc. for C19H19NiN2Br: C, 55.14; H, 4.59; Br,
19.31; N, 6.77; Ni, 14.18%. M.p. (dec.) 149 °C; yield
85%.
3.2.1.3. Bis-mesityl-nickel-2,2%-bipyridine. 1H-NMR
(CDCl3, ppm): l 8.56–8.57 (m, 2H), 8.33–8.37 (d, 2H),
7.79–7.82 (m, 2H), 7.28–7.31 (m, 2H), 6.45 (m, 4H,
C6H2), 2.59 (s, 12H, CH3), 2.17 (s, 6H, CH3). Anal.
Found: C, 74.08; H, 6.83; N, 6.28; Ni, 12.37. Calc. for
C28H30NiN2: C, 74.19; H, 6.62; N, 6.18; Ni, 12.96%.
M.p. (dec.) 215 °C; yield 81%.
3.2.2. Nickel catalysed electrosynthesis of triorganyl
phosphines from organic halides and chlorophosphines
The anode was a magnesium or zinc cylindrical rod
(diameter 1.3 cm) surrounded by a cylindrical nickel
grid. The electrosyntheses were carried out according to
the following procedure. The solution of Bu4NBF4
(0.005 mmol), NiBr2bipy (1 mmol), aryl or heteroaryl
halide (15 mmol) in DMF (40 ml) was electrolysed at
i=500 mA under argon until the whole ArX was
consumed. During the electrolysis the chlorophosphine
was continuously added dropwise with the rate of 1 mol
of phosphine per 2F of electricity (Ph2PCl) or 1 mol of
phosphine per 4F of electricity (PhPCl2). The progress
of the reaction was checked by GC analysis of samples.
The solution was hydrolysed using 0.1 N NH4Cl and
extracted with ether; the organic layer was washed with
water and dried; and the solvent was evaporated. The
products were purified by column chromatography on
silica gel with pentane–ether mixtures as eluent.
3.2. Preparati6e electrolyses
3.2.1. Electrochemical reduction of NiBr2bipy in
presence of aromatic bromides
A solution for electrolysis was prepared by mixing
0.1875 g (0.5 mmol) NiBr2bipy and 1 mol of aromatic
bromide in DMF. 2-BrTol (0.12 ml, 1 mmol) and
MesBr (0.075 ml, 0.5 mol or 0.15 ml, 1 mmol) were
used for the preparation of Tol2NiBrbipy, MesNiBr-
bipy and Mes2Nibipy, respectively. Electrolysis was car-
ried out in an electrochemical cell both with separation,
and without separation of anode and cathode compart-
ments at ambient temperature at the potential of a
working electrode −1.52 V. The amounts of electricity
passed through the electrolyte were 3e, 2e or 4e per
molecule of nickel complex for the preparation of
Tol2NiBrbipy, MesNiBrbipy and Mes2Nibipy, respec-
tively. After completing the electrolysis, the solution
was hydrolysed and extracted with ether; the organic
layer was washed with water and dried; and the solvent
was evaporated.
3.2.3. Nickel catalysed electrosynthesis of
organophosphorus compounds with PꢀC bonds from
white phosphorus and organic halides
The single-compartment cell was fitted with a cylin-
drical magnesium, zinc or aluminium rod (diameter 1.3
cm) as an anode, surrounded by a platinum cylinder as
a cathode. The solution of Bu4NBF4 (0.005 mmol),
NiBr2bipy or Ni(BF4)2bipy (0.5 mmol), organic halide
(35 mmol) and 7 mmol of white phosphorus dispersed
in DMF (100 ml) was electrolysed at 0.5 mA cm−2

192
Y.H. Budniko6a et al. / Journal of Organometallic Chemistry 630 (2001) 185–192
cathodic current density in an atmosphere of argon
until the whole RX was consumed. The solution was
hydrolysed using 0.1 N NH4Cl and extracted with
ether; the organic layer was washed with water and
dried; and the solvent was evaporated. Individual prod-
ucts were isolated from the mixture by column chro-
matography on silica gel and were identified by
measuring physical constants and spectra according to
appropriate literature data. In some experiments the
relative content of organophosphorus compounds was
estimated according to the integral intensity of the
31P-NMR spectrum.
Acknowledgements
This work was supported by the INTAS program,
grant 00-0018.
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3.2.4. Electrochemical reduction of nickel complexes in
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of 30 ml was prepared by dissolving 0.5 mmol of a
nickel complex (0.1875
g NiBr2bipy or 0.35 g
Ni(BF4)2bipy3) and 0.5 mol of supporting electrolyte
1.05 g Et4NBr (in the case of NiBr2bipy) or 1.085 g
Et4NBF4 (in the case of Ni(BF4)2bipy3) in DMF. In the
resulting solution, 0.062g (2 mmol) of white phospho-
rus was dispersed under argon when heated to 50 °C.
The electrolysis has been carried out in a two-compart-
ment electrochemical cell in potentiostatic regime (−
1.52 or −1.60 V). The amounts of electricity passed
through the electrolyte were 2e per molecule of nickel
complex. After completing the electrolysis, the precipi-
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vacuum at a temperature of 30 °C.
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3.2.4.1. Complex [NiP3Nibipy]Br2. Anal. Found: C,
21.69; H, 2.03; Br, 31.78; N, 4.52; Ni, 21.90; P, 16.65.
Calc. for C10H8N2Ni2P3Br2: C, 22.79; H, 1.52; Br,
30.40; N, 5.32; Ni, 22.29; P, 17.67%. 31P-NMR: −
335.8 (s). H-NMR (CDCl3, ppm): l 6.63–8.82 (m, 8H,
2,2%-bipy). M.p. (dec.) 154° C; yield 0.11 g (84%).
1
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3.2.4.2. Complex [NiP3Nibipy](BF4)2. Anal. Found: C,
21.50; H, 1.98; B, not determined; F, 27.2; N, 6.01; Ni,
19.34; P, 17.60. Calc. for C10H8N2Ni2P3B2F8: C, 22.22;
H, 1.48; B, 4.01; F, 28.15; N, 5.19; Ni, 21.74; P, 17.22%.
1
31P-NMR 31P: −334.6 (s). H-NMR (CDCl3, ppm): l
6.63–8.82 (m, 8H, 2,2%-bipy). M.p. (dec.) 148 °C; yield
0.12 g (89%).
.