The influence of the sacrificial anode nature on the mechanism of electrochemical arylation and alkylation of white phosphorus

Article abstract of DOI:10.1023/A:1021611926712

The material of the sacrificial anode has a substantial effect on the nature and yield of the target products of electrochemical phosphorylation of organic halides by white phosphorus in the presence of the nickel complexes with 2,2′-bipyridine. The use of the zinc anode results in the products with tricoordinated phosphorus, viz., triorganylphosphines, the reaction on the aluminum anode affords triorganylphosphine oxides, and the presence of Mg ²⁺ ions in the reaction mixture provides the transformation of white phosphorus into cyclic phosphines (PhP)₅.

Full text of DOI:10.1023/A:1021611926712

Russian Chemical Bulletin, International Edition, Vol. 51, No. 11, pp. 2059—2064, November, 2002
2059
The influence of the sacrificial anode nature on the mechanism
of electrochemical arylation and alkylation of white phosphorus
D. G. Yakhvarov,a Yu. H. Budnikova,a,bꢀ D. I. Tazeev,a,b 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 2) 75 2253. Eꢀmail: yulia@iopc.knc.ru
bKazan State University,
18 ul. Kremlevskaya, 420008 Kazan, Russian Federation.
Fax: +7 (843 2) 31 5416
The material of the sacrificial anode has a substantial effect on the nature and yield of the
target products of electrochemical phosphorylation of organic halides by white phosphorus in
the presence of the nickel complexes with 2,2´ꢀbipyridine. The use of the zinc anode results in
the products with tricoordinated phosphorus, viz., triorganylphosphines, the reaction on the
aluminum anode affords triorganylphosphine oxides, and the presence of Mg2+ ions in the
reaction mixture provides the transformation of white phosphorus into cyclic phosphines (PhP)5.
Key words: white phosphorus, nickel, zinc, 2,2´ꢀbipyridine, organic halide, electrochemiꢀ
cal catalysis, sacrificial anode.
on a PIꢀ50ꢀ1 potentiostat with a PRꢀ49 programmer and an
electrochemical cell connected by the threeꢀelectrode scheme.
The curves were detected with linear potential scan sweeps of
50 mV s–1 on a twoꢀcoordinate recorder. An Ag/0.01 М AgNO3
system in MeCN served as a reference electrode. A Pt wire 1 mm
in diameter was used as an auxiliary electrode. Measurements
were performed in a cell with a constant temperature (25 °С) in
an argon atmosphere.
Preparative electrolyses were carried out in a threeꢀelecꢀ
trode 40ꢀmL cell using a B5ꢀ49 constantꢀcurrent power source.
The potential of the working electrode was detected by a
Shch50ꢀ1 constantꢀcurrent voltmeter with respect to a reference
electrode, Ag/0.01 М AgNO3 in MeCN. The working surface of
a cylindrical Pt cathode was 20.0 cm2. Zinc, aluminum, and
magnesium rods, whose working surfaces were thoroughly
cleaned with an emery paper before electrolysis, were used as
anodes. During electrolysis the electrolyte was stirred with a
magnetic stirrer in an argon flow.
31Р NMR spectra were recorded on a Bruker СХРꢀ100 highꢀ
resolution spectrometer (Germany) at a frequency of 40.5 MHz
relatively to the external standard (85% H3PO4) with positive
downfield chemical shifts. 1Н NMR spectra were obtained on a
Varian Тꢀ60 instrument (60 MHz) using Me4Si as the internal
standard. ESR spectra were detected on a Radiopan SE/Xꢀ2544
Xꢀrange electronic spectrometer (Poland) using diphenylꢀ
picrylhydrazyl (DPPH, g = 2.0036) as the external standard.
The solvent MeCN was purified by triple fractional distillaꢀ
tion above Р2О5 with an addition of KMnO4. The concentration
of residual water was 1•10–3 mol L–1. Dimethylformamide was
purified by triple vacuum distillation with intermediate drying
above calcined K2CO3 and molecular sieves. In order to prepare
the supporting electrolyte, twice recrystallized salts (Et4NBr, from
MeCN and Et4NBF4, from EtOH) were used, which were dried
for 2 days in a vacuum desiccator at 100 °С. Benzene and diethyl
The problem of selective tetrahedron opening in white
phosphorus (P4) and its direct functionalization gains inꢀ
creasing significance due to a search for new ecologically
safe routes of syntheses of organophosphorus compounds.
It is known1—3 that organometallic compounds, e.g.,
RMgX and PhLi, cleave the Р—Р bond of the Р4 tetraꢀ
hedron to form a mixture of organophosphorus products
in 5—70% yields.
Undivided processes using easily oxidized metals, such
as Mg, Al, or Zn, as anodes well recommended themꢀ
selves for electrosyntheses, including electrocatalytic
functionalization of organic halides (RX). In these proꢀ
cesses, the nature of sacrificial anodes plays an important
role and often determines the selectivity and mechanism
of the process.4 Studies of routes of electrocatalytic transꢀ
formation of substrates involving sacrificial anodes have
been started rather recently. Understanding of mechaꢀ
nisms of these reactions is necessary for the development
of new methods for syntheses of various organic and
organoelement derivatives.
This work is aimed at studying the route of Р4 transforꢀ
mation and the influence of the sacrificial anode nature
on the mechanism of electrochemical arylation and alkyꢀ
lation of Р4 by electrochemically generated Ni0 complexes
in the presence of RX or related σꢀorganyl complexes.
Experimental
In cyclic voltammetric (CV) studies, a stationary diskꢀshaped
glassyꢀcarbon electrode with a working surface area of 3.14 mm2
was used as a working electrode. Voltammograms were recorded
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1903—1909, November, 2002.
1066ꢀ5285/02/5111ꢀ2059 $27.00 © 2002 Plenum Publishing Corporation

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Yakhvarov et al.
ether were dehydrated by distillation above Na, and CHCl3 was
dehydrated by boiling above P2О5 followed by distillation.
White phosphorus was purified using the following proceꢀ
dure: Р4 (10 g) was placed in a flask containing a mixture of
benzene (10 g) and Py (10 g), and the resulting mixture was
refluxed for 2 h in a box in an argon atmosphere. Then the
procedure was repeated with the next portion of solvents, after
which P4 was refluxed for 2 h more in distilled water (20 g). For
convenience, purified P4 was molded from a melt using a glass
syringe to form small rods with a weight of ∼1 g each. Prior to the
reaction, P4 was twice successively washed with anhydrous acꢀ
etone, EtOH, and Et2O.
The NiBr2bpy and Ni(BF4)2bpy3 complexes were syntheꢀ
sized from the corresponding nickel salt and a required amount
of 2,2´ꢀbipyridine in EtOH. Organic halides used as substrates
were commercial reagents (reagent grade) purified by distillaꢀ
tion to unchanged physicochemical constants. The purification
of (BuO)3РО used as a label was carried out by heating to 100 °С
with Na for 4 h followed by triple vacuum distillation.
Electrochemical reduction of NiIIbpy3 in the presence of white
phosphorus and organyl halide. A working solution 40 mL in
volume was prepared by dissolution of Ni(BF4)2bpy3 (0.35 g,
5•10ћ–4 mol), organyl halide (RX, 0.03 mol), and Еt4NBF4
(0.87 g, 4•10–3 mol) in DMF (or MeCN). Phosphorus (0.186 g,
6•10–3 mol) was emulgated to the resulting solution on heating
to 50 °C in an argon atmosphere. Electrolysis was carried out in
an undivided electrochemical cell with the Mg, Al, or Zn anode
under thermostatic conditions with a current density on the cathꢀ
ode of 5—10 mA cm–2 and a controlled cathodic potential of
–1.60 V (vs. Ag/0.01 M AgNO3 in MeCN) corresponding to the
reduction of the NiIIbpy3 complex to the Ni0bpy2 complex. An
amount of electricity of 1 A h (6 e per P atom) was passed through
the electrolyte. After the end of electrolysis, the reaction mixture
was treated with a 2 М solution of HCl; electrolysis products
were extracted with ether, and the ether was evaporated. In some
experiments with the Mg anode, the treatment of the reaction
mixture with a 2 М solution of HCl resulted in the formation of a
precipitate, which was filtered off and analyzed by elemental
analysis and spectroscopy. The relative content of organophosꢀ
phorus compounds in the ether extract was estimated from the
integral intensity of 31Р NMR spectral signals relatively to the
(BuO)3РО label. The percentage yield of each compound was
calculated from the overall preparative yield of the products.
Triorganylphosphines and triorganylphosphine oxides were sepaꢀ
rated by recrystallization from EtOH. The yields of the isolated
products are presented in Table 1. The physicochemical characꢀ
teristics of the obtained compounds correspond to published data.
Electrochemical reduction of the nickel complexes in the presꢀ
ence of white phosphorus. A working solution (catholyte) 30 mL
in volume was prepared by the dissolution in DMF of the
nickel complex (5•10–4 mol) with 2,2´ꢀbipyridine (0.1875 g of
NiBr2bpy or 0.35 g of Ni(BF4)2bpy3) and a supporting electrolyte
(5•10–3 mol), viz., 1.05 g of Et4NBr (in the case of Ni(BF4)2bpy3,
1.085 g of Et4NBF4). In the resulting solution, phosphorus
(0.062 g, 2•10–3 mol) was emulgated in an argon atmosphere at
50 °С. Electrolysis was carried out in a divided cell in the
potentiostatic regime at –1.52 or –1.60 V (vs. Ag/0.01 М AgNО3
in MeCN) at 50 °С in an argon atmosphere. During electrolysis
the catholyte was stirred with a magnetic stirrer. A saturated
DMF solution of the supporting electrolyte, which was used in
the catholyte, served as an anolyte. After the end of electrolysis
Table 1. Products of electrochemical functionalization of white
phosphorus by the Ni0 complexes with bpy obtained from
Ni(BF4)2bpy3
RX
Anode/solvent
Zn/DMF
Product
Yield by P (%)
PhI
Ph3P
65
12
10
50
10
40
18
50
10
9
60
15
38
10
8
Ph2PH
PhPH2
Ph3P
Ph3PO
Ph3P
Ph3PO
Ph3P
Ph3PO
Ph2PH
(PhP)5
Ph3P
Ph3P
Ph3PO
Ph3P
Ph3PO
Bu3P
Bu3PO
Bu3PO
Hex3PO
Mg/DMF
Al/DMF
Zn/DMF
PhBr
Mg/DMF
Al/DMF
Al/MeCN
Mg/DMF
60
11
55
38
46
BuBr
Al/MeCN
Al/MeCN
HexI*
* Hex is nꢀC6H13.
(2 е electricity per Ni atom corresponding to 27 mA h passed
through the solution), the precipitate was filtered off, washed
with diethyl ether, and dried in a vacuum desiccator at 30 °С.
The [NiP3Nibpy]Br2 complex (0.11 g) was obtained from
NiBr2bpy in 84% yield, m.p. 154 °С (decomp.). Found (%):
C, 21.69; H, 2.03; Br, 31.78; N, 4.52; Ni, 21.90; P, 16.65.
C10H8Br2N2Ni2P3. Calculated (%): C, 22.79; H, 1.52; Br, 30.40;
1
N, 5.32; Ni, 22.29; P, 17.67. 31Р NMR, δ: –335.8. H NMR
(CDCl3), δ: 6.63—8.82 (m, 8 H, 2,2´ꢀbipyridine).
The [NiP3Nibpy](BF4)2 complex (0.12 g) was obtained from
Ni(BF4)2bpy3 in 88% yield, m.p. 148 °С (decomp.). Found (%):
C, 21.50; H, 1.98; B (was not determined); F, 27.2; N, 6.01;
Ni, 19.34; P, 17.60. С10H8B2F8N2Ni2P3. Calculated (%):
C, 22.22; H, 1.48; B, 4.01; F, 28.15; N, 5.19; Ni, 21.74; P, 17.22.
31Р NMR, δ: –334.6. 1H NMR (CDCl3), δ: 6.63—8.82 (m, 8 H,
2,2´ꢀbipyridine).
Results and Discussion
Electrolyses of solutions of RX in DMF or MeCN in
the presence of the NiIIbpy3 complex and an emulsion of
Р4 showed that the electrochemically generated catalysts
(the Ni0 complexes with bpy) can transform Р4 into comꢀ
pounds bearing P—C bonds, that is, phosphines and phosꢀ
phine oxides (see Table 1). The following reactions are
known4,5 to occur at the electrodes during electrolysis
(Scheme 1).
By analogy to the previously studied functionalizations
of Р4 by the Grignard reagents, we can assume that the
key step of the process is the interaction of Р4 with the

Sacrificial anodes in electrochemistry
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 11, November, 2002 2061
Scheme 1
оꢀMeC6H4Br the reaction of оꢀMeC6H4NiBrbpy or
MesNiBrbpy with Р4 in DMF affords one compound
probably containing lowꢀcoordination phosphorus:
ArP=Nibpy (δР 204), which was not isolated, however,
because of its low stability. A similar compound forms by
the electroreduction of PhPCl2 in the presence of NiIIbpy3
(from Ni(BF4)2bpy3) (δР 206). The attempt to isolate this
compound from a solution results in its decomposition to
ArP(O)(OH)H (δР 20, JP,H = 531 Hz).
Cathode: NiIIL3 + 2 e
Anode: M – n e
Ni0L2 + L, L = bpy
Mn+, n = 2, 3; M = Mg, Zn, Al
P4 + RX
>P—R
organonickel compound RNiIIXbpyn (n = 1, 2), which
includes the sequence of reactions (Scheme 2).
The P4 tetrahedron opening and the cleavage of other
Р—Р bonds occur, most probably, by the Ni0 (or NiII)
complexes to form nickel phosphides and polyphosphides.
For example, it is known6 that the [NiL]2+ complex (L is
MeC(CH2PPh2)3) is a sufficiently strong base to substiꢀ
tute one of the P atoms in the tetrahedral cluster of P4 to
form the [LNi(P3)NiL](BF4)2 complex (1) stable in the
air and containing the δꢀР3 cyclotriphosphorus group
(Scheme 3).
Scheme 2
Ni0bpyn + RX
RNiIIbpyn–1
X
>P—R + NiIIbpyX
n = 1, 2
Depending on the RX nature and experimental condiꢀ
tions, the nickel(II) complex is completely or partially
regenerated during preparative electrolysis. For example,
when the Al anode is used, a portion of nickel removes
from the reaction due to the formation of insoluble nickel
phosphides, whose elemental composition is close to
Ph2PNiBr•NiBr2. The treatment with concentrated acids
can completely transfer these precipitates to a solution to
form diorganylphosphinic acid.
Scheme 3
2 Ni(BF4)2 + P4 + L
•
Ph2PNiBr(NiBr2) + HCl + O2
→
→ Ph2P(O)OH + 2 NiII + 3 Br– + Cl–.
In this study, we have chosen PhBr, oꢀBrC6H4Me
(oꢀBrTol), and Me3C6H2Br (MesBr) as model ArX. The
use of such a series of substrates makes it possible to
model and compare the reaction routes involving interꢀ
mediates (Ni0 complexes), which differ in stability due
to the presence or absence of the Me group in the
orthoꢀposition of the benzene ring.
Subsequent reactions of Р—С bond formation should
occur similarly , as in the case of the primary attack to Р4
of the organonickel compound PhNiIIXbpyn (n = 1, 2).
In order to consider other possible routes of appearꢀ
ance of the Р—R bonds, we studied the interaction of Р4
with the NiII and Ni0 complexes in the absence of RX.
It is known that the nonpolar tetrahedral molecule Р4
is characterized by a weak nucleophilicity (due to the lone
electron pairs at the P atoms) and a weak electrophilicity
(due to the vacant lowꢀlying dꢀorbitals7). It was estabꢀ
lished8,9 that Р4 can act as the η1ꢀ or η2ꢀligand. A tetraꢀ
hedral molecule is activated during η1ꢀcoordination to
transform into a trigonal pyramid, whose vertex is diꢀ
rected toward the metal atom. As a result of η2ꢀcoordinaꢀ
tion, the edge bound to the metal elongates by ∼0.25 Å
compared to the Р—Р bond in the free molecule (2.21 Å).
The bidentate coordination of Р4 favors a stronger activaꢀ
tion of the molecule than the monodentate coordination
does. For bidentate bonding of Р4 the Р—Р distance is
0.14 Å longer than that for monodentate bonding, proꢀ
viding a considerable loosening of the Р4 tetrahedron.
Therefore, the coordinationally saturated metal complexes
(in our case, nickel complexes) incapable of η2ꢀcoordinaꢀ
tion of Р4 are characterized by a lower catalytic activity
In order to confirm the sequence of reactions (see
Scheme 2), the step of electrochemical formation of the
organonickel compound RNiIIXbpyn (n = 1, 2) and the
step of functionalization of Р4 by the latter were sepaꢀ
rated. It was found that the products of phosphorus
arylation formed by the treatment of Р4 with a minor
excess of PhNiIIXbpyn (obtained by the twoꢀelectron reꢀ
duction of the NiIIbpy complex from NiBr2bpy in the
presence of PhBr with a Ni : PhBr molar ratio of 1 : 2). In
particular, the products with three Р—С bonds, viz., a
mixture of Ph3P and Ph3PO (1 : 1), and a small amount
on insoluble nickel phosphides with the elemental comꢀ
position close to that given above are formed. However,
PhNiIIXbpyn decomposes rapidly, and its concentraꢀ
tion in a solution cannot be monitored. Rather stable
σꢀcomplexes obtained from оꢀMeC6H4Br and MesBr
are more convenient for studying. A mixture of phosꢀ
phines and phosphine oxides was also obtained when
оꢀMeC6H4NiBrbpy and MesNiBrbpy were used as model
compounds. It is of interest that in the absence of

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Yakhvarov et al.
i/µA
than the coordinationally unsaturated complexes, which
are capable of both η1ꢀ and η2ꢀcoordination.9 According
to the quantumꢀchemical calculations,10 the nonpolar
molecule is activated due to coordination: the energy of
the Р—Р bonds decreases nonuniformly, and effective
charges appear on the P atoms. Coordinated Р4 (unlike
free P4) becomes a stronger electron acceptor and is readily
reduced by the Ni0 complexes.
–75
–50
–25
0
C2
2
C1
3
1
The behavior of NiBr2bpy and Ni(BF4)2bpy3 in the
presence of Р4 was studied to evaluate the complexꢀformꢀ
ing properties of the Р4 molecule and its reactivity toward
the bipyridine complexes of nickel in different oxidation
states. On adding a saturated solution of P4 in benzene to a
solution of the NiIIbpy complex in DMF, the second reꢀ
versible peak (Е = –2.2 V) disappears and the first peak of
reduction of the nickel complex is divided into two peaks.
25
A2
A1
1
2
–E/V
Fig. 1. Cyclic voltammetry of the electrochemical reduction of
NiBr2bpy (0.01 mol L–1) in DMF with Et4NBF4 (0.1 mol L–1
as a supporting electrolyte in the absence (1) and presence of Р4
(0.01 mol L–1) (2) and of the latter solution after its storage in
an argon atmosphere for 1 day (3).
)
C
1
The potential of the first of them Ер = –1.38 V shifts to
The solution blackens rapidly upon the preparative
electrochemical reduction of NiIIbpy (from NiBr2bpy) to
Ni0bpy in the presence of Р4. After exhaustive electrolysis
(2 e per NiII complex molecule), a black amorphous preꢀ
cipitate forms in an electrolyte solution. This precipitate
is poorly soluble in organic solvents and has the elemental
composition C10H8Br2N2Ni2P3. We believe that it repreꢀ
sents binuclear complex 2.
–1.29 V on storing the solution for 1 day. The second peak
C
2
Ер = –1.52 V corresponds to the reduction of the initial
NiBr2bpy complex (Fig. 1). An increase in the P4 concenꢀ
tration in a solution results in an increase in the current at
potentials of the electrochemically irreversible first caꢀ
thodic peak (C1) and a proprotional decrease in the curꢀ
rent of the second peak (C2) with a simultaneous decrease
in its anodic component (А2). However, a new anodic
A
1
peak appears at Ер = –0.35 V. The change in the morꢀ
phology of the voltammetric curves can be explained as
follows. In the general case, if both the initial compound
and reduction product are complexes of nickel in different
oxidation states and the overall reduction process is close
to reversible or quasiꢀreversible, the direction and value of
the shift of the peak should depend on the relative stability
of components of this redox pair, the difference in their
coordination numbers, and the equilibrium constant. It is
known11,12 that in the presence of organophosphorus
ligands the reduction peaks of the NiII complex shift toꢀ
ward negative potentials. This is assumed to indicate that
the reduced form of the metal produces a stronger comꢀ
plex than the oxidized form does. The reversible process
Compound 2 was characterized by the 31Р (δР –335)
and 1Н NMR spectra in CDCl3 (the spectrum consists of
a complicated multiplet in the region of signals from aroꢀ
matic protons δH 6.8—8.9). The ESR spectrum of this
complex shows that this compound is paramagnetic: the
signal has a broad maximum.
Ni2+(P4)bpy + 2 e
Ni0(P4)bpy
The single irreversible cathodic peak in the CV curve
of a saturated solution of the isolated [NiP3Nibpy]Br2
complex in DMF (∼3•10–4 mol L–1) (Fig. 2) at
ЕрC = –1.67 V (Ер – Ер/2 = 250 mV) lies in the region of
reduction potentials of the NiII and NiI complex with
bpy. The reverse potential scan results in the appearance
of a small poorly reproducible anodic peak at –0.9 V.
Since the reduction potential of compound 2 is someꢀ
what more negative than that of NiBr2bpy and its solubilꢀ
ity in DMF is low (a considerable portion of compound 2
precipitates during electrolysis), high yields of the nickel
complex with cyclotriphosphorus can be achieved in the
reaction of the Ni0 complex with Р4. This complex reacts
rapidly with RX. For example, the treatment with PhI
affords a new orangeꢀbrown complex (δР –293), which is
becomes irreversible (the disappearance of the anodic
component of the peak), probably, due to the fast subseꢀ
quent chemical reduction of P4 coordinated to Ni0, which
acts as the electron donor
Ni0(P4)bpy → Nin+[P4]n–bpy.
This fast reaction shifts the reduction potential of the
NiIIbpy complex from its standard reduction potential
toward less negative potentials. As shown below, the preꢀ
parative reduction of Р4 by the electrochemically generꢀ
ated Ni0bpy complexes corroborated this assumption. The
products of Р4 cathodic reduction, [P4]n–, are oxidized
probably at a potential of –0.35 V (see Fig. 1).

Sacrificial anodes in electrochemistry
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 11, November, 2002 2063
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the reaction of dihalophosphines with metallic Mg afꢀ
fords14 cyclic structures [R—P<]n, and the chemical
functionalization of P4 by the Grignard reagents in the
presence of RX (see Refs. 2 and 15) also gives polycyclic
phosphines (R—P)n, the most stable of which are the
compounds with five P atoms (Scheme 4).
–20
–15
C
–10
–5
0
Scheme 4
P4 + R—MgBr + R—Br
(R—P)n
A
5
1
2
–E/V
When PhI is used (see Table 1), phosphine (PhP)5
does not form as the final product. Cyclic polyphosphines
probably form in this case as well. However, due to a
higher reactivity of PhI (compared to PhBr), the intermeꢀ
diate products are further functionalized to form addiꢀ
tional two Р—С bonds at the P atom.
Thus, the experimental data point to the important
role of metal ions in the mechanism of phosphorus tetraꢀ
hedron opening and transformation of phosphorus oligoꢀ
mers into the final products. Let us consider in which
steps of the overall process (Scheme 5) the anodically
generated Zn2+, Mg2+, and Al3+ ions can be involved. It
can be assumed that the metal ions act as electrophilic
reagents, thus stabilizing phosphide anions 4 formed by
the Р—Р bond cleavage (Eqs. (1)—(4)). This reaction
competes with the reactions of phosphide anion 4 with the
Ni2+ ions or organic halide ArX (see Scheme 5, Eq. (5)).
The Ni2+ ions are present in minor amounts and, hence,
their role is substantial mainly at the initial steps of elecꢀ
Fig. 2. Cyclic voltammetry of a saturated solution of
[NiP3Nibpy]Br2 (3•10–4 mol L–1) in DMF with Et4NBF4
(0.1 mol L–1) as a supporting electrolyte.
also poorly soluble in organic solvents and, being isolated
from a solution, decomposes to form PhP(O)(OH)H
(δР 27, JP,H = 530 Hz). This fact confirms indirectly
that the reaction of complex 2 with PhI involves the
phenylation of the cyclotriphosphorus fragment with a
probable formation of mononuclear complex 3.
This is another possible route for the formation of the
Р—Ph bonds, which is alternative to the reaction of the
σꢀaryl PhNiXbpyn complex with Р4.
Scheme 5
Anode: Zn – 2 e
ZnII
(1)
(2)
(3)
The results of preparative electrosyntheses show that
the nature of the sacrificial anode substantially affects the
nature of organophosphorus compounds (OPC). The use
of the Zn anode results in the complete conversion of P4
to soluble phosphorus compounds, mainly to tertiary
phosphines (R3P) and, to a less extent, to diarylꢀ and
monoarylphosphines (see Table 1). In the case of the Al
anode, the general yield of soluble OPC is lower and a
considerable part of them is presented by phosphine oxꢀ
ides. Such an occurrence of the process is probably assoꢀ
ciated with the possibility of formation in the solution of
strong Lewis acids. In this case, the anodically generated
Al3+ ions can act as strong Lewis acids (as shown13 for the
reaction of ButCl with Р4 in the presence of AlCl3). The
magnesium anode, like the zinc anode, favors the formaꢀ
tion of tricoordinated phosphorus compounds in a high
yield. However, in the presence of PhBr, the cyclic
polyphosphorus compound (PhP)5 with the less strained
cycle is mainly formed. It is known2,14,15 that the Mg2+
ions favor the formation of the (PhP)5 fragments due to
the stabilization of cyclic polyphosphines. For example,
Cathode: NiIIbpy + 2 e
Ni0bpy
Ni0bpy + ArX
ArNiXbpy
+ ArNiXbpy
+ Ni2+Xbpy (4)
(5)

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Yakhvarov et al.
trolysis when the concentration of the Zn2+ (Mg2+, Al3+
)
with Р4 should result in the cleavage of the Р—Р bonds
and in further transformations similar to those described
above involving RNiXbpy.
Thus, the electrolysis in an undivided electrochemical
cell with the sacrificial anode of Mg, Al, or Zn allows the
functionalization of Р4 under mild conditions to form comꢀ
pounds with the Р—С bonds. The purposeful choice of the
material of the sacrificial anode makes it possible to influꢀ
ence, to some extent, on the nature and yield of the final
products of electrochemical arylation and alkylation of Р4.
ions is low. The reaction of the phosphide anion with RX
([RX] >> [M2+]) affords products with the P—C bonds
and is one of the main routes of P4 functionalization.
Among known metal phosphides, only phosphides of
Zn and alkaline metals react16 efficiently with RX. Nickel
phosphides, as well as Al and Mg phosphides, are much
less reactive. Therefore, the contribution of formation of
nickel phosphide 6 to the P4 tetrahedron opening is likely
rather small. Zinc phosphides 5 react readily with various
RX via nucleophilic substitution (Scheme 6). This results
in the successive cleavage of the P—P bonds in phosphoꢀ
rus oligomers to afford aryl(alkyl)phosphines as the final
products.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos. 01ꢀ03ꢀ
33210a and 01ꢀ15ꢀ99353), the Joint Program of the CRDF
Foundation and the Ministry of Education of the Russian
Federation "Fundamental Research and High Education"
(Research and Educational Center of KSU, REC 007),
the Complex Program of the Russian Academy of Sciꢀ
ences "New Principles and Methods of Development and
Target Synthesis of Substances with Specified Properꢀ
ties," and INTAS (Grant 00ꢀ0018).
Scheme 6
5 + ArX
+ ZnX2
Another possibility of participation of the Zn2+, Mg2+
,
and Al3+ ions generated at the anode in the catalytic
transformation of P4 is transmetallation, i.e., substitution
of nickel in σꢀorganyl complexes. For example, crossꢀ
coupling reactions of RX involving the stage of catalytic
formation of organozinc compounds were described17:
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will be described in detail elsewhere. Here we would like
to note that we proposed the mechanism of formation of
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voltammetry and preparative electrolysis (Scheme 7).
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Scheme 7
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The Ni0bpy complex can react with RX in the bulk
solution to yield RNiXbpy and thus close the catalytic
cycle. The reaction of the organozinc complex RZnXbpy
Received June 20, 2001;
in revised form April 12, 2002