Electrocatalytic reduction of aryldichlorophosphines with the (2,2′-bipyridine)nickel complexes

Article abstract of DOI:10.1007/s11172-007-0142-9

The reduction of aryldichlorophosphines in organic solvents was studied by cyclic voltammetry, preparative electrolysis, and chemical reduction. The reaction of the electrochemically generated (2,2′-bipyridine)nickel(0) complexes with aryldichlorophosphines PhPCl₂ and tippPCl₂ (tipp is 2,4,6-triisopropylphenyl) proceeds through the formation of highly reactive organophosphorus intermediates, whose reactions with diphenylacetylene and hex-1-ene afford phosphirene and phosphirane heterocycles, respectively.

Full text of DOI:10.1007/s11172-007-0142-9

Russian Chemical Bulletin, International Edition, Vol. 56, No. 5, pp. 935—942, May, 2007
935
Electrocatalytic reduction of aryldichlorophosphines
with the (2,2´ꢀbipyridine)nickel complexes
D. G. Yakhvarov,aꢀ E. HeyꢀHawkins,b R. M. Kagirov,a Yu. H. Budnikova,a
Yu. S. Ganushevich,a and O. G. Sinyashina
aA. E. Arbuzov Institute of Organic and Physical Chemistry,
Kazan Research Center of the Russian Academy of Sciences,
8 ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843) 273 2253. Еꢀmail: yakhvar@iopc.knc.ru
bInstitute of Inorganic Chemistry, Leipzig University,
29 Johannisallee, Dꢀ04103 Leipzig, Germany.*
Fax: +49 (034) 973 9319. Eꢀmail: hey@rz.uniꢀleipzig.de
The reduction of aryldichlorophosphines in organic solvents was studied by cyclic
voltammetry, preparative electrolysis, and chemical reduction. The reaction of the electroꢀ
chemically generated (2,2´ꢀbipyridine)nickel(0) complexes with aryldichlorophosphines PhPCl2
and tippPCl2 (tipp is 2,4,6ꢀtriisopropylphenyl) proceeds through the formation of highly reacꢀ
tive organophosphorus intermediates, whose reactions with diphenylacetylene and hexꢀ1ꢀene
afford phosphirene and phosphirane heterocycles, respectively.
Key words: phosphines, nickel complexes, phosphinidenes, cyclic voltammetry, electroꢀ
reduction, reduction.
The search for new highly efficient synthetic methods
is one of the principal trends of the chemistry of organoꢀ
metallic and organophosphorus compounds.1 The formaꢀ
tion of element—carbon bonds, especially phosphoꢀ
rus—carbon bond, is an important goal of the modern
organoelement chemistry.2,3 In this context, special atꢀ
tention is given to the development of novel approaches
to the target synthesis of chemical compounds from highly
reactive organophosphorus intermediates. Examples of
such intermediates are derivatives of lowꢀcoordinate phosꢀ
phorus, viz., phosphinidenes [RP:] (phosphorus analogs
of carbenes), which play a significant role in the synthesis
of earlier unknown organophosphorus and heterocyclic
compounds.3—5 In preparative synthesis these shortꢀlived
species are used, as a rule, as transition metal complexes.
Presently the main and most appropriate method for their
generation is the thermal decomposition of the correꢀ
sponding tungsten and molybdenum 7ꢀphosphanorbornaꢀ
diene complexes.6
center attracted attention of researchers to the practical
use of the nickel complexes in organic and organophosꢀ
phorus synthesis9—11 and made it possible to improve the
methods for synthesis of biologically active compounds
and useful ligands. An alternative method using the
[R—P—W(CO)5] intermediates (R = Ar, Alk) and inꢀ
cluding the step of subsequent demetallation of the obꢀ
tained organophosphorus product4,5,12 is less convenient.
A possibility of the direct synthesis of free phosphiranes
and phosphirenes has been demonstrated for the first time
using as an example the relatively stable nickelphosphinꢀ
idene complex9 containing the sterically hindered ligand
and the substituent at the phosphorus atom.10,11 Howꢀ
ever, the synthesis of this complex is difficult and consists
of several steps: the formation of primary phosphine
[(dtbpe)Ni(P(H)dmp)] (dtbpe is 1,2ꢀbis(diꢀtertꢀbutylꢀ
phosphino)ethane, and dmp is 2,6ꢀdimesitylphenyl), its
subsequent oxidation with tropilium hexafluorophosphate,
and further deprotonation with NaN(SiMe3)2.9 Thus, this
method is more complicated than the known method for
synthesis of phosphanorbornadiene, which prevents its
wide propagation in the synthetic practice.
Many publications are focused to the direct synthesis
of various stable metal phosphinidene complexes7,8 and
investigation of their reactivity toward various organic
and organoelement compounds.8,9 Recently discovered
reactions of metalꢀphosphinidene species of the new type
related to the phosphinidene group transfer from the metal
In the recent time, we are developing a new approach
based on the electrochemical generation of phosphinidene
particles in the system containing the nickel complex with
2,2´ꢀbipyridine (bpy) and aryldichlorophosphines. These
complexes are known as highly efficient catalysts of variꢀ
ous electrochemical coupling processes that allow one to
* Institut für anorganische Chemie der Universität Leipzig,
29 Johannisallee, Dꢀ04103 Leipzig, Germany.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 901—907, May, 2007.
1066ꢀ5285/07/5605ꢀ0935 © 2007 Springer Science+Business Media, Inc.

936
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
Yakhvarov et al.
Table 1. Potentials (Ep) and currents (Ip) of the reduction (C)
and reꢀoxidation (A) peaks in the CV curves of the [NiCl2(bpy)]
complex and dichlorophosphines (GC electrode, DMF/0.1 M
Bu4NBF4)
synthesize organic and organophosphorus compounds of
various types.13—15 In some cases, the formation of
phosphinidene particles, which act as intermediates of
electrocatalytic processes involving organophosphorus reꢀ
actants and white phosphorus, is detected in situ.13,14
In the present work, we describe the reduction of
aryldichlorophosphines PhPCl2 and tippPCl2 (tipp is
2,4,6ꢀtriisopropylphenyl) by the electrochemically genꢀ
erated [Ni(bpy)n] complexes (n = 1, 2), affording highly
reactive phosphorusꢀcontaining intermediates that maniꢀ
fest the properties of the phosphinidene complexes.
Comꢀ
pound
Peak
–Ep
/V
Ip
/µA
Theoretical
number of electrons
[NiCl2(bpy)] C1
1.47
1.30
2.18
2.08
1.62
—
–44
41
–20
17
–32
—
–22
—
2
2
1
1
2
—
2
—
A1
C2
A2
PhPCl2
C3
A3
C4
A4
Results and Discussion
tippPCl2
1.68
—
Cyclic voltammetry (CV). The electrochemical reducꢀ
tion (ER) of the [NiCl2(bpy)] complex occurs via a reꢀ
versible twoꢀstep transfer of three electrons (Fig. 1,
Table 1, Eqs (1) and (2)).
Note. The CV data obtained without IRꢀcompensation are preꢀ
sented here and in Table 2.
process, which agrees with published data.17 Several
mechanisms of the ER of substituted phosphines under
various conditions have been proposed previously.18—20
In some cases, the formation of a free phosphinidene
species as an intermediate of the electrochemical process
was postulated.17,18 It was also shown19 that the cathodic
reduction can generate cyclic polyphosphines of the
(RP)n type (R = Ar, Alk; n = 4—6).
The CV curve of a mixture of the [NiCl2(bpy)] comꢀ
plex with PhPCl2 (1 : 1 molar ratio) exhibits the appearꢀ
ance of a new irreversible reduction peak (C3) at more
anodic values than the potential of the first reduction
peak of the starting nickel complex (Fig. 2, Table 2). In
this case, based on the CV data (appearance of the
preꢀpeak C3) and earlier conclusions,20 one can judge
about the interaction of phenyldichlorophosphine with
the nickel(II) complex. The absence of the reduction peak
of the free ligand (see Table 1, Ep(C3) = –1.62 V) and
unchanged C1/A1 and C2/A2 peaks indicate the quantitaꢀ
tive reduction of coordinated PhPCl2 at potentials of the
C3 preꢀpeak (see Fig. 2). In addition, it can be assumed
[NiCl2(bpy)] + 2 e
[Ni(bpy)] + 2 Cl–
[Ni(bpy)]•–
(1)
(2)
[Ni(bpy)] + e
The first reversible reduction peak (C1) corresponds to
the twoꢀelectron reduction step of transformation of
the [NiCl2(bpy)] complex into the [Ni(bpy)] complex
(see Eq. (1)). The second peak (C2) is attributed to the
oneꢀelectron reversible reduction of [Ni(bpy)] to the
[Ni(bpy)]•– radical anion complex (see Eq. (2)). The
data obtained by ESR spectroscopy (g = 2.007)16 show
that in this particle the electron is predominantly localꢀ
ized on the ligand. As a whole, the electrochemical beꢀ
havior of this complex is similar to that of the earlier
described16 [NiBr2(bpy)] complex under similar electroꢀ
chemical conditions.
As can be seen from the presented results (see Table 1),
the ER of the aryldichlorophosphines considered occurs
at more negative potentials (see Fig. 1) than the potential
of the NiII/Ni0 system and is an irreversible twoꢀelectron
I/µA
C1
I/µA
C2
C3
–40
–20
0
C1
1 e
–60
C2
1 e
C4
C3
–40
–20
0
A2
20
A2
A1
A1
–1.5
–1.0
–1.5
–2.0
E/V
–1.0
–2.0
E/V
Fig. 1. CV curve of the [NiCl2(bpy)] complex (5•10–3 mol L–1
)
in DMF in the presence of Bu4NBF4 (10–1 mol L–1); dash line
shows the CV curve of PhPCl2 (5•10–3 mol L–1) in the same
solution.
Fig. 2. CV curve of the [NiCl2(bpy)] complex (5•10–3 mol L–1
)
in DMF in the presence of PhPCl2 (5•10–3 mol L–1) and
Bu4NBF4 (10–1 mol L–1).

Electroreduction of aryldichlorophosphines
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
937
Table 2. Potentials (Ep) and currents (Ip) of the reduction (C)
and reꢀoxidation (A) peaks in the CV curves of the [NiCl2(bpy)]
complex (5•10–3 mol L–1) in the presence of ArPCl2 (5•10–3
mol L–1) (GC electrode, DMF/0.1 M Bu4NBF4)
I/µA
C3
–60
C2
1 e
–40
ArPCl2
PhPCl2
Peak
–Ep
/V
Ip
/µA
Theoretical
number of electrons
C1
–20
0
C1
A1
C2
A2
C3
C4
C1
A1
C2
A2
C3
A3
1.47
1.37
2.18
2.08
1.21
1.88
1.44
1.36
2.18
2.09
1.88
0.72
–41
21
–20
11
–36
–4
–31
20
–6
4
2
—
1
—
2
—
2
—
1
A2
A1
A3
–1.0
–1.5
–2.0
E/V
tippPCl2
Fig. 3. CV curve of the [NiCl2(bpy)] complex (5•10–3 mol L–1
in the presence of tippPCl2 (5•10–3 mol L–1) and Bu4NBF4
(10–1 mol L–1).
)
1
2
—
–33
5
the presence of tippPCl2 taken in a molar ratio of 1 : 1
showed that the substrates considered reacted according
to a mechanism different from that of PhPCl2. This folꢀ
lows from a comparison of the character of the CV curves
(Fig. 3, Table 2). The absence of the preꢀpeak indicates
that no coordination of phosphine with the nickel comꢀ
plex occurs in this case. However, an irreversible reducꢀ
tion peak (C3) appears at –1.88 V in the CV curve of the
nickel complex in the presence of tippPCl2 (see Figs 2
and 3). In this case, the peaks of reduction and reꢀoxidaꢀ
tion of the [NiCl2(bpy)] complex are retained but an adꢀ
ditional reꢀoxidation peak А3 appears (Ep(А3) = –0.72 V).
Evidently, the twoꢀelectron irreversible reduction of
tippPCl2 occurs at a potential of –1.88 V.
The rise of the С3 peak (see Fig. 3) can also be due to
the reduction of a new compound (probably, an organoꢀ
nickel intermediate) containing the nickel—phosphorus
σꢀbond, as it was exemplified for some organic halides.13,14
This peak corresponds, most likely, to the reduction of
σꢀorganonickel complex 1 formed via the oxidative addiꢀ
tion of tippPCl2 to the [Ni(bpy)] complex at one of the
P—Cl bonds (Scheme 2).
that the phosphorusꢀcontaining product of PhPCl2 reꢀ
duction rapidly escapes from the coordination sphere of
the metal to regenerate the initial complex. However, it is
very difficult to make any conclusions about the mechaꢀ
nism of the process (electron transfer to PhPCl2 via
the metal ion or directly from the electrode) and the
nature of the formed product (phosphinidene [RP:] or
R(Cl)P—P(Cl)R, or other coupling species).
It was established that the ER of PhPCl2 can occur
not only in the coordination sphere of the nickel complex
at the potential of the C3 peak but also as an interaction in
the solution bulk with the electrochemically generꢀ
ated [Ni(bpy)] complex at the potential of the C1 peak
(Scheme 1).
Scheme 1
Scheme 2
Sterically hindered aryldichlorophosphine containing
the bulky 2,4,6ꢀtriisopropylphenyl substituent at the phosꢀ
phorus atom has been used in an attempt to stabilize the
organophosphorus intermediate in the coordination sphere
of the nickel complex. The voltammetric study of the
electrochemical behavior of the [NiCl2(bpy)] complex in
tipp is 2,4,6ꢀtriisopropylphenyl (2,4,6ꢀPri3C6H2)
Possibly, the twoꢀelectron reduction of species 1 at a
potential of –1.88 V or by [Ni(bpy)] could result in the

938
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Yakhvarov et al.
elimination of two chloride anions to form nickelꢀ
phosphinidene complex 2 as an intermediate of the proꢀ
cess (Scheme 3).
The fourꢀelectron preparative ER of tippPCl2 was carꢀ
ried out at the controlled potential of the working elecꢀ
trode from –1.3 to –1.4 V (Ag/AgNO3 (0.01 mol L–1)) in
the galvanostatic regime. When 4 F electricity were
passed, the reaction mixture contained primary phosphine
tippPH2 and compound 4 containing coordinated diꢀ
phosphene, whose yield was 46 and 21%, respectively.
Probably, primary phosphine is also the reaction product
of the organophosphorus intermediate with molecules of
the supporting electrolyte and protonꢀdonor admixtures.
The formation of complex 4 can be presented as a result
of the interaction of two nickelphosphinidene particles
of 2 (see Scheme 3) followed by the elimination of the
[Ni(bpy)] complex (Scheme 5) by analogy to the formaꢀ
tion and dimerization of similar electrophilic phosphinꢀ
idene iron complexes formed by the reduction of the corꢀ
responding dichlorophosphines.22
Scheme 3
Thus, four electrons per one tippPCl2 molecule or two
molecules of the [Ni(bpy)] complex should be consumed
for the generation of the phosphinidene complex from
[NiCl2(bpy)].
Macroscale electrolysis. The preparative ER of PhPCl2
and the [NiCl2(bpy)] complex in a molar ratio of 1 : 1 in
DMF in the presence of Bu4NBF4 (0.1 M) affords priꢀ
mary phosphine PhPH2 and diphosphene unit coordiꢀ
nated to the nickel center21 (3) (Scheme 4).
Scheme 5
Scheme 4
Chemical reduction. We carried out the chemical reꢀ
duction of tippPCl2 with the [Ni(bpy)2] complex, and the
results obtained were compared with those for the ER
(i.e., in the presence of the supporting electrolyte). As
shown above, the ER of dichlorophosphine tippPCl2 reꢀ
quires two equivalents of the [Ni(bpy)] complex generꢀ
ated in situ (see Schemes 2 and 3). The [Ni(bpy)2] comꢀ
plex was synthesized using the electrochemical technique
to perform chemical reduction (Scheme 6).
Perhaps, primary phosphine is formed by the reaction
of the product of twoꢀelectron reduction of PhPCl2,
namely, phosphinidene particle [PhP:] (Eq. (3)), with the
cations of the supporting electrolyte or protonꢀdonor adꢀ
mixtures (Eq. (4)), as it has been described earlier.18
Scheme 6
PhPCl2 + 2 e
[PhP:] + 2 Cl–
(3)
The electrochemical method makes it possible to synꢀ
thesize and isolate in good yield the highly reactive
[Ni(bpy)2] complex from the simple nickel salts (for
example, NiCl2). This method is efficient and conveꢀ
nient and finely supplements the earlier described proꢀ
cedures of synthesis of the nickel(0) complexes with
2,2´ꢀbipyridine including the use of K4Ni(CN)4 in liquid
nitrogen23 or the ligand exchange reaction in the correꢀ
sponding [Ni(cod)2] complex (cod is cyclooctaꢀ1,5ꢀ
diene).24
+
[PhP:] + 2 NBu4
2 Bu3N + PhPH2 + 2 EtCH=CH2
(4)
The presence of butꢀ1ꢀene and tributylamine in the
reaction medium was found by GLC.
It should be mentioned that diphosphene complex 3
can be formed by the dimerization of the phosphinidene
complexes. Similar examples have also been described
earlier.21

Electroreduction of aryldichlorophosphines
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
939
The use of two equivalents of bipyridine is necessary
to stabilize the nickel atom in the low oxidation state in
order to level the possible disproportionation between two
[Ni(bpy)] complexes coordinately unsaturated with reꢀ
spect to bipyridine16 (Eq. (5)).
and acetylene afford phosphaketene, phosphiranes,
and phosphirenes, respectively, and the nickel(0) comꢀ
plexes.10,11 However, the chemical properties of the
nickelphosphinidene complex considered and the mechaꢀ
nism of interaction have been studied only partially up to
presently.11
It seemed of interest to study the formation of
phosphinidene species in the coordination sphere of
the nickel complexes using scavengers. In the experiꢀ
ments carried out, the phosphorusꢀcontaining interꢀ
mediates were generated in situ by the reaction of the
electrochemically synthesized [Ni(bpy)2] complex with
tippPCl2 (molar ratio 2 : 1) in the presence of 10ꢀfold
excess diphenylacetylene as the scavenger. As a result,
products 6 and 7 were obtained in a molar ratio of ~1 : 1
(Scheme 9).
2 [Ni(bpy)]
[Ni(bpy)2] + Ni
(5)
After tippPCl2 was added to a solution of the [Ni(bpy)2]
complex in toluene at –70 °С in the absence of ions of the
supporting electrolyte, the reaction mixture was slowly
warmed to ~20 °C with continuous stirring. In this
case, virtually no primary phosphine is formed and only
small amounts of diphosphine (tippHP)2 and threeꢀmemꢀ
bered phosphorus cyclic compound (tippP)3 were found
(Scheme 7).
Scheme 7
Scheme 9
The presence of small amounts of the homocoupling
product, namely 1,2ꢀdichlorodiphosphine, compound 5,
can be due to the intermediate formation of complex 1 by
oxidative addition and its subsequent reaction with
tippPCl2 (Scheme 8).
Minor amounts of (tippPCl)2 and (tippP)3 were also
found. The formation of diphosphetene 7 can be due to
the insertion of the phosphinidene fragment at one of the
Р—С bonds of primarily formed phosphirene 6. This type
of interaction is possible for the electrophilic phosphinꢀ
idene complexes. It is known25,26 that similar 1,2ꢀdiꢀ
phosphetenes can be obtained according to the mechaꢀ
nism including the insertion of the phosphinidene interꢀ
mediate into the phosphirene heterocycle.
Scheme 8
The formation of phosphirane 8 is observed under
similar conditions for the reaction in the presence of hexꢀ
1ꢀene (Scheme 10).
Scheme 10
Reactions of the phosphorus intermediates with scavenꢀ
gers. It has been found rather recently10 for the unique
nickelphosphinidene complex [(dtbpe)Ni=P(dmp)] that
this type of complexes is prone to the phosphinidene group
transfer in the reactions with various reactants. The reacꢀ
tions of this complex with carbon monoxide, ethylene,

940
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Yakhvarov et al.
The working electrode for preparative syntheses was the
GC electrode with a working surface of 60 cm2. NMR spectra
were recorded on a Bruker 400 highꢀresolution spectrometer.
ESR spectra were measured on an SE/Xꢀ2544 Xꢀrange electron
spectrometer (RADIOPAN). Melting points were determined
on an Electrothermal IA9000 SERIES Digital Melting Point
Apparatus instrument in capillaries under nitrogen. The nickel
content in selected samples was determined by atomic adsorpꢀ
tion analysis on a Carl Zeiss AAS1 spectrometer.
Synthesis of [NiCl2(bpy)] complex. A solution of bpy (1.97 g,
12.6 mmol) in EtOH (15 mL) was added to a solution of
NiCl2•6H2O (3 g, 12.6 mmol) in EtOH (25 mL) at ~20 °C.
After stirring for 6 h, a pale green precipitate formed was filtered
off, washed with EtOH (3×20 mL), and dried in vacuo for 8 h.
The yield was 3.02 g (84%). Found (%): C, 41.85; H, 2.63;
Cl, 24.54; N, 9.58; Ni, 21.02. C10H8Cl2N2Ni. Calculated (%):
C, 41.97; H, 2.79; Cl, 24.83; N, 9.79; Ni, 20.64.
2,4,6ꢀTriisopropylphenyldichlorophosphine. Magnesium turnꢀ
ings (11.4 g, 0.45 mol) were placed in a roundꢀbottom flask
(1000 mL), and the content of the flask was three times evacuꢀ
ated on heating followed by filling with argon. Then freshly
distilled diethyl ether (350 mL) was poured and 1ꢀbromoꢀ2,4,6ꢀ
triisopropylbenzene (120 g, 0.42 mol) was dropped at ~20 °C.
The reaction start was determined from boiling of the ether
on the surface of the magnesium turnings. Several drops of
1,2ꢀdibromoethane were added to the reaction medium to actiꢀ
vate magnesium. The mixture was stirred for 14 h, after which it
became turbid and gray. The resulting solution was carefully
filtered and transferred to a dropping funnel and then added
dropwise to a solution of PCl3 (62 g, 0.45 mol) in diethyl ether
(100 mL). After stirring for 14 h, the precipitate formed was
filtered off and the filtrate was left for 10 h at –4 °C. The
obtained yellowish needleꢀlike crystals of tippPCl2 were filtered
off and dried in vacuo. The yield was 97.4 g (76%), m.p. 85—95 °C
(cf. Ref. 29: m.p. 90—100 °C). 31Р NMR (C6D6), δ: 165.2. The
spectrum also contained an admixture signal at δ 160.0 correꢀ
sponding to tippPClBr.
It should be mentioned that the phosphorusꢀcontainꢀ
ing intermediates formed in the reaction medium are abꢀ
solutely inert toward electrophilic reagents (DMF, acꢀ
etone). Only the (tippP)3 triphosphorus cycle is formed in
the reaction mixture, whereas no products of the Wittig
reaction or [2+2]ꢀcycloaddition characteristic of the nuꢀ
cleophilic phosphinidene complexes are observed.
It should be emphasized that the formation of
phosphiranes, phosphirenes, and triphosphorus cycles can
be a result of the interaction of a free phosphinidene
species with unsaturated organic substrates. Similar inꢀ
termediates were proposed earlier27 for the reactions
of aryldichlorophosphines bearing substituents in the
orthoꢀposition of the aromatic ring. We performed the
chemical reduction of tippPCl2 with sodium or magneꢀ
sium to prove the formation of the phosphinidene interꢀ
mediate in the coordination sphere of nickel. The major
product was (tippP)3. There were several attempts to trap
and introduce the free phosphinidene species into the
reaction using chemical reagents, including unsaturated
compounds.27,28 However, no formation of phosphiranes
and phosphirenes was observed under these conditions.
In summary, the results obtained and respective conꢀ
clusions illustrate new possibilities for using the electroꢀ
chemical methods to generate highly reactive phosꢀ
phorusꢀcontaining intermediates. The formation of the
phosphirane and phosphirene heterocycles as the reacꢀ
tion products of these intermediates with scavengers can
be highly valuable from the viewpoint of development of
new methods for the synthesis of organophosphorus comꢀ
pounds.
Experimental
Electrochemical reduction of [NiCl2(bpy)] in the presence of
ArPCl2. Solutions containing the [NiCl2(bpy)] complex (65 mg,
0.23 mmol), ArPCl2 (0.23 mmol) (70 mg of tippPCl2 or 41 mg of
PhPCl2), and Bu4NBF4 as the supporting electrolyte (659 mg,
2.0 mmol) in DMF (20 mL) were prepared for electrolysis.
Electrochemical reduction was carried out in the galvanostatic
regime in a divided cell at ~20 °C. The potential of the working
electrode ranged from –1.3 to –1.4 V (Ag/0.01 M AgNO3).
A direct current of 24.7 mA was passed through the working
solution for 1 h. After the end of electrolysis, the solvent was
removed in vacuo and the reaction products were extracted from
the residue with toluene (5×20 mL). Toluene was evaporated in
part from the extract, and the toluene layer was decanted from
the residues of DMF and the supporting electrolyte. After the
toluene extract was concentrated, organophosphorus products
All experiments were carried out under dry nitrogen. Solꢀ
vents were purified by distillation prior to use. Dimethylꢀ
formamide was dried over calcium hydride followed by distillaꢀ
tion in vacuo. The supporting electrolyte salt Bu4NBF4 was dried
by melting in vacuo and stored under dry nitrogen. Phenylꢀ
dichlorophosphine and 2,2´ꢀbipyridine were purchased from
Aldrich.
In CV studies, a stationary glassy carbon (GC) disc elecꢀ
trode with a working surface of 3.14 mm2 was used as the workꢀ
ing electrode. The CV curves were recorded with switching on
the electrochemical cell according to the threeꢀelectrode scheme.
The curves were detected in DMF against a 0.1 M solution of
Bu4NBF4 on an EG&G Princeton Applied Research, model
273A potentiostat and a LINSEIS LY 1400 twoꢀcoordinate reꢀ
corder with a potential sweep of 50 mV s–1. The reference elecꢀ
trode was an Ag/0.01 M AgNO3 system in MeCN (Е°(Fc/Fc+) =
+0.20 V). A Pt wire with a diameter of 1 mm served as the
auxiliary electrode. Measurements were carried out in a temꢀ
peratureꢀcontrolled (20 °С) cell under nitrogen. Preparative elecꢀ
trolysis was carried out at 20 °С on the same electrochemical
setup in a 30ꢀmL threeꢀelectrode cell under divided electrolysis
conditions in DMF containing a 0.1 M solution of Bu4NBF4.
were extracted from the residue with pentane. As a result,
1
PhPH2
(
31Р NMR (C6D6), δ: –124.8 (t, JP,H = 200 Hz)) and
diphosphene complex 3 (31Р NMR (C6D6), δ: +14.0 (s)) were
obtained in 52 and 17% yields, respectively.
Electrochemical synthesis of the [Ni(bpy)2] complex. The
[NiCl2(bpy)] complex (338 mg, 1 mmol), bpy (156 mg, 1 mmol),
and the Bu4NBF4 supporting electrolyte (659 mg, 2.0 mmol)
were dissolved in DMF (20 mL). The electrolysis of the resulting
solution was carried out in the divided cell at the potential of the

Electroreduction of aryldichlorophosphines
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 5, May, 2007
941
working electrode from –1.48 to –1.52 V (Ag/0.01 M AgNO3).
A direct current of 26.8 mA was passed through the solution
for 2 h. After the end of electrolysis, the solvent was evaporated
in vacuo and a product, which crystallized from the solution on
cooling to –35 °C, was extracted from the dark violet residue
with toluene (5×20 mL). The crystals were filtered off and dried
in vacuo. The yield was 237 mg (64%), m.p. 154 °C (cf. Ref. 24:
m.p. 155 °C). Found (%): C, 64.68; H, 4.43; N, 15.14; Ni, 15.68.
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C
20H16N4Ni. Calculated (%): C, 64.74; H, 4.35; N, 15.09;
Ni, 15.90.
Reaction of [Ni(bpy)2] with tippPCl2. A solution of tippPCl2
(76 mg, 0.25 mmol) in toluene (15 mL) was added to a solution
of [Ni(bpy)2] (186 mg, 0.5 mmol) in toluene (25 mL) at –70 °C
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(C6D6), δ: –99.6 (d, 1JP,P = 178 Hz); –132.9 (t, 1JP,P = 178 Hz)),
1
tippPH2
(tippPH)2
(
31Р NMR (C6D6), δ: –158.9 (t, JP,H = 204 Hz)),
1
(
31Р NMR (C6D6), δ: –111.9 (dd, JP,H = 149 Hz,
1
2
2JP,H = 70 Hz); –116.4 (dd, JP,H = 149 Hz, JP,H = 70 Hz)),
and (tippPCl)2 (31Р NMR (C6D6), δ: +77.7, +75.4 (both s)).
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engers. A solution containing tippPCl2 (76 mg, 0.25 mmol) and
2.5 mmoles of the scavenger (444 mg of diphenylacetylene,
210 mg of hexꢀ1ꢀene, and 183 mg of DMF or 145 mg of acetone)
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cooled to –70 °C. The solution was slowly heated to ~20 °C.
The precipitate formed was filtered off, and the solvent
was removed in vacuo. The following products were obꢀ
tained: 1ꢀ(2,4,6ꢀtriisopropylphenyl)ꢀ2,3ꢀdiphenylphosphirene
(6) (31P NMR (C6D6), δ: –172.1 (s)), 1,2ꢀbis(2,4,6ꢀtriisopropylꢀ
phenyl)ꢀ3,4ꢀdiphenylꢀ1,2ꢀdiphosphetene (7) (31P NMR (C6D6),
δ: –42.6 (s)), and 1ꢀ(2,4,6ꢀtriisopropylphenyl)ꢀ2ꢀbutylphosꢀ
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This work was financially supported by the German
Research Society (DFG, Grant 436 RUS 17/53/03), Reꢀ
search and Educational Center "Materials and Technoloꢀ
gies of the 21st Century" of the Kazan State University
(Grant REC 007), INTAS (Grant YSF 03ꢀ55ꢀ2050), and
the Russian Foundation for Basic Research (Project
No. 06ꢀ03ꢀ32247ꢀa).

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Received April 17, 2006;
in revised form March 14, 2007