Activation of white phosphorus in the coordination sphere of nickel complexes with σ-donor ligands

Article abstract of DOI:10.1007/s11172-005-0338-9

Routes of white phosphorus activation in the coordination sphere of the nickel complexes with different ligands are shown. The first route is based on the coordination of a P₄ molecule with the metal, resulting in the deformation of the P₄ tetrahedron without destruction. This case is characteristic of the NiX₂L complexes, which are reduced at higher cathodic potentials (|E_red| > 0.9 V) (X = BF₄, Br, and Cl; L is bpy in DMF, MeCN, and acetone; 2,9-dimethyl-1,10-phenanthroline (phen) and PPh₃ in DMF and acetone). To cleave the P-P bonds in the P ₄ molecule, this complex should be reduced on the electrode. The second route is the oxidation of white phosphorus in the coordination sphere of the Ni^II complex. It occurs when the complex has a sufficiently high oxidizing ability and is reduced rather easily (|E_red| < 0.9 V) (X = BF₄, L is 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) in acetone; 1,1′,5,5′-bis[methylenedi(p-phenylene)]di(3,7-diphenyl-1,5- diaza-3,7-diphosphacyclooctane) (n²p²) in DMF; phen and PPh₃ in MeCN). The P₄ molecule opening is observed to form a new Ni^I complex containing the (P₃) fragment, for example, [(triphos)Ni(P₃)Ni(triphos)](BF₄)₂.

Full text of DOI:10.1007/s11172-005-0338-9

942
Russian Chemical Bulletin, International Edition, Vol. 54, No. 4, pp. 942—947, April, 2005
Activation of white phosphorus in the coordination sphere
of nickel complexes with σꢀdonor ligands*
a
a
a
Yu. G. Budnikova,a D. I. Tazeev, A. G. Kafiyatullina, D. G. Yakhvarov,
ꢀ
V. I. Morozov,a N. K. Gusarova,b B. A. Trofimov,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. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843 2) 75 2253. Eꢀmail: yulia@iopc.knc.ru
bA. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences,
1 ul. Favorskogo, 664033 Irkutsk, Russian Federation.
Fax: +7 (395 2) 39 6046
Routes of white phosphorus activation in the coordination sphere of the nickel complexes
with different ligands are shown. The first route is based on the coordination of a P4 molecule
with the metal, resulting in the deformation of the P4 tetrahedron without destruction. This
case is characteristic of the NiX2L complexes, which are reduced at higher cathodic potentials
(|Ered| > 0.9 V) (X = BF4, Br, and Cl; L is bpy in DMF, MeCN, and acetone; 2,9ꢀdimethylꢀ
1,10ꢀphenanthroline (phen) and PPh3 in DMF and acetone). To cleave the P—P bonds in the
P4 molecule, this complex should be reduced on the electrode. The second route is the
oxidation of white phosphorus in the coordination sphere of the NiII complex. It occurs when
the complex has a sufficiently high oxidizing ability and is reduced rather easily (|Ered| < 0.9 V)
(X
= BF4, L is 1,1,1ꢀtris(diphenylphosphinomethyl)ethane (triphos) in acetone;
1,1´,5,5´ꢀbis[methylenedi(pꢀphenylene)]di(3,7ꢀdiphenylꢀ1,5ꢀdiazaꢀ3,7ꢀdiphosphacyclooctane)
(n2p2) in DMF; phen and PPh3 in MeCN). The P4 molecule opening is observed to form a new
NiI complex containing the (P3) fragment, for example, [(triphos)Ni(P3)Ni(triphos)](BF4)2.
Key words: white phosphorus, nickel complexes, activation, cyclic voltammetry, electroꢀ
chemistry.
The electrochemical activation of reagents in processes
related basis organophosphorus compounds, i.e., the main
task of the elemental phosphorus chemistry is the direct
transformation of phosphorus into organophosphorus
compounds (OPC), excluding traditional steps of its chloꢀ
rination. At the same time, metal complexes with polyꢀ
phosphorus ligands can possess a set of useful properties:
semiconductivity, corrosion resistance, and others7 and
act as stable intermediates in various reactions, which are
of independent interest.
In this work, we attempted to estimate the reactivity of
several nickel complexes with σꢀdonor ligands toward
white phosphorus using cyclic voltammetry (CV), preꢀ
parative electrolysis, and 31P NMR spectroscopy. The
nickel complexes were chosen, because they are catalysts
of some reactions of white phosphorus functionalization,
for instance, arylation8,9 and alkoxylation.10
involving organometallic compounds is very efficient.1—4
This approach combines advantages of catalysis by metal
complexes and activation by means of electrochemical
electron transfer. The activation of white phosphorus is a
practically important task because of the necessity to
search for new routes of direct syntheses of organophosꢀ
phorus compounds. Numerous reactions of P4 tetrahedron
transformation were described, which resulted in various
polyphosphorus structures among which metal complexes
with cyclic P3, P5, and P6 ligands,4 as well as the P4
ligand,5,6 seem to be most interesting. The P4 molecule is
activated due to the deformation of the P4 tetrahedron
and, as a consequence, the P—P bond length changes. In
ultimate cases, these bonds can cleave to form new
polyphosphorus structures. Until now, P4 transformation
was studied only by NMR spectroscopy, and very stable
compounds were examined. Evidently, the more stable
these structures, the more difficult is the preparation of
To establish the mechanism of activation of the P4
molecule in the coordination sphere of the nickel comꢀ
plexes, we estimated changes in the electrochemical paꢀ
rameters (reduction potential and current) of the comꢀ
plexes upon the addition of white phosphorus. Compounds
capable of stabilizing nickel in low oxidation states (+1, 0),
* Dedicated to the Academician V. I. Minkin on the occasion of
his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 919—924, April, 2005.
1066ꢀ5285/05/5404ꢀ0942 © 2005 Springer Science+Business Media, Inc.

Electrochemical activation of white phosphorus
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
943
Table 1. 31P NMR chemical shifts for solutions of Ni(BF4)2Ln in
DMF in the presence of white phosphorus (1 : 1) for L = bpy,
phen, and PPh3 (n = 3) and [NiL(P3)NiL](BF4)2 for L = triphos
and n2p2
such as bpy, PPh3, phen, 1,1,1ꢀ(trisdiphenylphosphinoꢀ
methyl)ethane (triphos), and n2p2, were chosen as ligands.
Experimental
31
Stationary disk glassyꢀcarbon electrode with the efficient
surface area of 3.14 mm2 was used as the working electrode in
electrochemical studies (CV). Voltammograms were detected
using a PIꢀ50ꢀ1 potentiostat with a PRꢀ49 programmer and an
electrochemical cell switchedꢀon via a threeꢀelectrode scheme.
Curves were recorded at a linear potential sweep of 50 mV s–1 on
a twoꢀcoordinate recorder. An Ag/0.01 M AgNO3 system in
MeCN served as the reference electrode. A platinum wire 1 mm
in diameter was used as the auxiliary electrode. Measurements
were carried out in a cell at the temperature kept constant at
25 °C under argon.
Ln
δ P NMR
free
I
II
[LNi(P3)NiL] (BF4)2
P4
phen
PPh3
bpy
triphos
n2p2
–323.8
–347.2
–363.1
—
–463.4
–487.2
–490
—
—
—
—
–523
–290
–375
—
—
Note. I —
, II —
.
31P NMR spectra were obtained with a Bruker MSLꢀ400
NMR Fourier spectrometer (Germany) at a frequency of
161 MHz relatively to the external standard (85% orthophosꢀ
phoric acid).
Electrochemical reduction of the NiIILnBr2 complexes (L =
bpy (n = 1), phen (n = 1), and PPh3 (n = 3)) in the presence of
white phosphorus. The working solution (40 mL) was prepared
by the dissolution of 10–3 moles of the nickel complex (0.36 g of
NiBr2bpy; 0.42 g of NiBr2phen; or 0.48 g of NiBr2(PPh3)3) and
5•10–3 moles of the supporting electrolyte (1.05 g of Et4NBr) in
DMF. White phosphorus (0.062 g, 5•10–4 mol) was suspended
with stirring of the solution under argon at 50 °C. Electrolysis
was carried out in a divided cell in the potentiostatic regime
(–1.60 V) vs. Ag/0.01 M AgNO3 in CH3CN at 50 °C under
argon. The catholyte was magnetically stirred during electrolyꢀ
sis. A saturated DMF solution of the supporting electrolyte served
as the anolyte. After the end of electrolysis (after the electricity
equal to 2e/(nickel atom) corresponding to 27 mA h passed
through the solution), a dark precipitate was filtered off, washed
with ether, and dried in a vacuum desiccator at 30 °C.
ESR spectra were recorded using a Radiopan SE/Xꢀ2544
spectrometer (Poland) with diphenylpicrylhydrazyl (DPPH,
g = 2.0036) used as the external standard. IR spectra were reꢀ
corded with a Bruker Vector 22 instrument. UV spectra were
obtained using a Specord UV VIS instrument.
Xꢀray powder diffraction analysis was carried out on a
D8 ADVANCE diffractometer with the CuꢀKα radiation (waveꢀ
length 1.5406 E; 40 kV, 30 mA) and a graphite monochromator.
A sample was scanned within 2θ = 3—70° with a scan increment
of 0.02°. The exposure time in a point was 1 s.
The elemental composition of nickel phosphides was deterꢀ
mined using an EMAL 2 laserꢀionization mass spectrometer.
Acetonitrile purified by triple fractional distillation above
P2O5 with an addition of KMnO4 was used. Dimethylformamide
was purified by triple vacuum distillation with intermediate dryꢀ
ing above molecular sieves. Acetone was distilled above KMnO4
and then above anhydrous CaCl2. To prepare the supporting
electrolyte, twice recrystallized salts were used: Et4NBr, Et4NCl
(from MeCN), and Et4NBF4 (from EtOH), which were dried in
a vacuum desiccator at 100 °C for 2 days. Benzene was distilled
above sodium. White phosphorus was recrystallized from a pyriꢀ
dine—benzene mixture.
A solution of white phosphorus was prepared by the dissoluꢀ
tion of the calculated amount of P4 in benzene in such a way
that the addition of 0.1 mL of this solution to the electrochemiꢀ
cal cell containing 5 mL of a solution of the studied metal
complex provided the P4 concentration in the cell equal to
5•10–3 mol L–1, i.e., the 1 : 1 stoichiometry with respect to the
metal complex concentration.
The complexes NiX2L were synthesized by the mixing of
equivalent amounts of a nickel salt and the corresponding ligand
in hot ethanol followed by the filtration of the complex and
drying in vacuo for a day.
The complexes Ni3P2bpy·3•H2O, Ni3P2phen•3 H2O, and
Ni3P2(CH3)2NCHO were synthesized.
Complex Ni3P2bpy·3•H2O. The yield was 0.35 g (89% calcuꢀ
lated based on P), m.p. 154 °C (decomp.). IR (Vaseline), ν/cm–1
:
769, 1382, 1468, 1662 (bpy). Found (%): C, 26.52; N, 6.43;
Ni, 39.64; P, 13.89. Calculated (%): C, 26.73; N, 6.23; Ni, 39.42;
P, 13.81. MS (Irel (%)): 449 [M]+ (100), 369 (30), 340 (28),
156 (52). XRD: d = 18 E (br.).
Complex Ni3P2phen•3 H2O. The yield was 0.23 g (46% calꢀ
culated based on P), m.p. 188 °C (decomp.). IR (Vaseline),
ν/cm–1: 747, 835, 841, 1417, 1524 (phen). Found (%): C, 28.17;
N, 5.72; Ni, 35.11; P, 12.51. C14H18N2Ni3P2O. Calculated (%):
C, 27.94; N, 5.59; Ni, 35.33; P, 12.37.
NiBr2, NiCl2, and Ni(BF4)2•6 H2O (reagent grade) and
PPh3, bpy, phen, and triphos were used as received. The n2p2
ligand was synthesized by a known procedure.11
Complex Ni3P2(CH3)2NCHO. The yield was 0.21 g (67%
calculated based on P), m.p. 258 °C (decomp.). Found (%):
C, 11.87; N, 4.57; Ni, 53.18; P, 22.36. C3H7NONi3P2. Calcuꢀ
lated (%): C, 11.54; N, 4.49; Ni, 56.73; P, 19.87.
Bis[1,1,1ꢀtris(diphenylphosphinomethyl)ethane]phosꢀ
phiridinonickel(II) bistetrafluoroborate [Ni2P3(triphos)2](BF4)2
and 1,1´,5,5´ꢀbis[methylenedi(pꢀphenylene)]di(3,7ꢀdiphenylꢀ
1,5ꢀdiazaꢀ3,7ꢀdiphosphacyclooctane)phosphiridinonickel(II)
bistetrafluoroborate [Ni2P3(n2p2)](BF4)2 were synthesized by a
previously described procedure.12
Results and Discussion
The data of 31P NMR spectroscopy of 5•10–2 M solutions of
Ni(BF4)2L in DMF in the presence of white phosphorus are
presented in Table 1.
Let us consider the electrochemical reduction (CV) of
the coordinately unsaturated complexes NiX2Ln (X = Br,

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Budnikova et al.
Table 2. Electrochemical characteristics of the reduction of the
ERed
NiX2L nickel complexes in the absence (EC ) and presence (EC ´
)
1
1
of P4 (Ni : P4 = 1 : 1)
P
4
ERed
–2
–1
0
Complex
(solvent)
Ligand
EС
EС ´
∆E
I
С ´/IС
1
1
1
1
/V
[Ni – P ]
NiBr2
(DMF)
—
bpy
–1.72
–1.35
–1.18
–1.03
–1.13
–0.97
–1.52
–0.62
–1.24
–0.47
–0.94
–0.30
–1.14
–1.26
–1.34
–1.17
–1.40
–0.81
–1.36
0.54
0.32
0.63
0.15
0.08
0.48
0.11
0
0.1
0.8
1.7
1.8
2.0
1.8
1.3
1.4
2.1
1.0
1.0
0.8
1.4
1.0
1.0
1.4
1.1
0.4
0.7
0.5
1.0
1.0
1.3
1.0
1.0
1.0
2.0
0.7
1.3
4
ERed
(PPh3)3 –1.76
Phen –1.12
triphos –1.60
—
bpy
(PPh3)3 –0.48
Phen –1.01
triphos –0.30
—
bpy
(PPh3)3 –1.75
Phen –1.44
triphos –1.63
—
bpy
(PPh3)3 –0.93
Phen –0.72
triphos –0.22
—
bpy
NiBr2
(MeCN)
–1.10
–1.35
0.07
0
[Ni – P ]
4
EOx
1
P
4
Ni(BF4)2
(DMF)
–1.77
–1.56
0.63
0.30
0.41
0.27
0.23
0.68
0.12
EOx
EOx
Fig. 1. Comparison of the reduction and oxidation potentials of
free white phosphorus and white phosphorus in the coordinaꢀ
tion sphere of the nickel complex.
Ni(BF4)2
(MeCN)
–1.49
–1.48
–1.25 –0.32
–1.20 –0.48
–0.41 –0.19
Nickel complexes NiX2Ln (Ln is bpy in DMF, MeCN,
and acetone; Ln is phen or (PPh3)3 in DMF and acetone).
A free P4 molecule is rather poorly polarized: the electroꢀ
chemical energetic gap ∆G 13 (the difference between the
reduction and oxidation potentials) is significant, being
3.79 V in MeCN and 3.30 V in DMF. The considerable
negative reduction potential of white phosphorus contribꢀ
utes greatly to the ∆G value (Fig. 1). Complex formation
is accompanied by a sharp decrease in ∆G and, hence, an
increase in the polarizability of the P4 molecule and its
ability to accept and donate electrons. The P4 ligand in
the coordination sphere of nickel is reduced and oxidized
much more easily, i.e., its reactivity increases.
When P4 is gradually added to a solution of the chosen
metal complex, the [Ni] : P4 ratio changes from 10 : 1 to
1 : 1 and the initial reduction peak decreases, while at less
negative potentials a peak appears. This peak corresponds
to the irreversible reduction of a new complex containing
the P4 molecule as a ligand (Fig. 2). For the ratio
[Ni] : P4 = 1 : 1, the initial peak disappears, and the new
peak reaches a maximum. The observed processes can be
described by Scheme 1.
NiCl2
(DMF)
–1.42
–1.55
–1.03
–1.43
–1.44
–1.08
–0.91
–0.87
–1.01
–0.91
0.39
0.12
0.15
0.04
0.19
0.48
0.64
0.19
(PPh3)3 –1.59
Phen
—
–1.12
–1.10
–1.35
Ni(BF4)2
(acetone)
bpy
(PPh3)3 –1.65
Phen –1.10
triphos –0.32
–0.81 –0.49
Cl, BF4, L = PPh3 (n = 3), bpy, phen, triphos, and n2p2
(n = 1)) in CH3CN, DMF, and acetone. The reversibility
of the process depends on the solvent: in MeCN the ratio
of heights of the oxidation to reduction currents (Ia/Ic) is
somewhat higher, i.e., Ni0L is more stable in solution.
The reduction potentials (EC1) of the complexes are preꢀ
sented in Table 2.
The addition of white phosphorus to solutions of the
chosen metal complexes shifts the potentials of the obꢀ
served reduction peaks to the region of less negative poꢀ
tentials or to the more cathodic region, which indicates
the formation of new complexes with different electroꢀ
chemical characteristics. As will be shown further, the
change in these characteristics along with the data of
preparative electrolysis and 31P NMR spectroscopy can
suggest the character of interaction of P4 with the metal
complexes under study.
Scheme 1
Let us divide all the studied complexes, which behave
differently in the presence of white phosphorus, into
groups.

Electrochemical activation of white phosphorus
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
945
C3
ligand, then the nickel(II) complex with P4 would be charꢀ
acterized by the reversible reduction peak, whose potenꢀ
tial is somewhat shifted relatively to that of the initial
complex. The observed irreversibility is related to the fast
subsequent transformation of white phosphorus in the
coordination sphere of the Ni0 complex.
C2
–I
C1´
C1
4
3
2
The data of 31P NMR spectroscopy indicate that in
polar aprotic solvents, e.g., DMF, white phosphorus exꢀ
ists as both the free P4 molecule (δP = –523) and the
η1ꢀcoordinated complex with the nickel atom. A similar
situation is observed for the Ni complexes with bpy,
PPh3, and phen (see Table 1). The broad signals with
δP = –320—–365 are attributed to the phosphorus atom
linked to nickel.4 The signals with δP at –460—–490 corꢀ
respond to three other phosphorus atoms in the coordiꢀ
1
C2
–E
A1
5
A2
–E
Fig. 2. Schematic cyclic voltammograms of the NiX2L nickel
complex with the σꢀdonor ligand in the absence (1) and presꢀ
ence of white phosphorus (2—4): P4 : Ni 1 : 2 (2), 1 : 1 (3), 2 : 1
and (4); 5, CV of solution 3 after passing 2 F electricity.
4
nated P4 molecule.
When P4 is added, the reduction of NiII to Ni0
becomes irreversible, which can be explained by the
fast subsequent chemical transformation of phosphorus
(route i, Scheme 1) in the coordination sphere of the Ni0
complex. A new C2 peak appears in the CV (see Fig. 2) at
more negative potentials with respect to the C1 peaks and
corresponds, most likely, to the reduction of the product
of the reaction between Ni0 and P4. Thus, P4 acts as both
the ligand and a substrate (reactant). The reduction poꢀ
tentials of the nickel salts and complexes in the presence
and absence of white phosphorus are presented in Table 2.
An increase in the P4 concentration over the stoichioꢀ
metric value, the reduction peak (C3) of the P4 itself
(E = –2.20 V in DMF) appears in the voltammogram,
and its height is proportional to the P4 concentration
(see Fig. 2).
The decrease in the reduction potential of the
NiX2(P4)L complex formed (see Fig. 2) as compared to
the initial one indicates a decrease in the LUMO due to
the donorꢀacceptor interaction in the NiLnX2—P4 pair,
where unoccupied dꢀorbitals of phosphorus can withdraw
a part of the electron density of the metal complex. It is
known that the addition of some substrates capable of
coordinating with metal to solutions of metal complexes
results in a change in the shape of the voltammetric curve,
namely, the disappearance of the reduction peak of the
initial metal complex and the appearance of and a gradual
increase in a new peak at less negative potentials. This is
observed, for instance, when acrylonitrile was added to
14
NiII—PPh3 or different phosphine ligands were added
In all cases considered for the NiX2Ln complexes with
bpy in DMF, MeCN, and acetone and with phen and
PPh3 in DMF and acetone, the P4 molecule is coordiꢀ
nated with the nickel atom acting as a ligand. White phosꢀ
phorus can be regenerated, most likely, in the unchanged
state from these systems.
In these cases, the only coordination of the phosphoꢀ
rus atom with metal is insufficient to cleave one or several
P—P bonds in P4. The NiIIL—P4 complex should be reꢀ
duced electrochemically to Ni0L—P4. It has previously9
been shown for NiBr2bpy that the P4 molecule is transꢀ
formed into the cycloꢀP3 ligand under the action of elecꢀ
trochemically generated Ni0. The reduction potential of
the [bpyNi(P3)Ni]Br2 complex formed by electrolysis
to the nickel salt.15 The saturation of the coordination
sphere of NiII with highꢀfield ligands (for example, comꢀ
pounds of tricoordinated phosphorus PIII) increases the
electron density on the metal atom. As a result, the HOMO
of NiII and LUMO of the ligand are brought together,
thus facilitating the removal of the ligand as an anion.
Due to the intramolecular oneꢀelectron transfer, the
hexacoordinated complex is completely ionized15
NiX2L3L´
NiL3L´2+ + 2X–.
The shift of equilibrium toward the cationic [NiL3L´]2+
complexes depends on the basicity of the σꢀdonor and its
volume and the nickel—ligand binding strength. The catꢀ
ionic [NiL3L´]2+ complexes are isostructural analogs of
coordinately saturated complexes of zeroꢀvalence nickel
[NiL3L´]0 with close bond lengths and bond angles. In
this pair of complexes, the activation energy of electron
transfer is very low, because no rearrangement of the coꢀ
ordination sphere is required and the electron transfer is
strictly reversible and occurs at a potential close to the
standard value for the NiII/Ni0 pair (with the correspondꢀ
ing ligands). If white phosphorus is a usual stable PIII
(EC = –1.72 V) (see Fig. 2, curve 5) corresponds to the
2
potential of the new peak, which was observed in the
voltammograms upon the addition of P4 to NiIIbpy (EC
–1.73 V) (see Fig. 2, curve 3).
=
2
It can be assumed that the formation of a black preꢀ
cipitate due to electrolysis is a consequence of a low staꢀ
bility of the primarily formed cycloꢀP3 complex, which
undergoes subsequent transformation into a more stable
form. On keeping the solution for 1 day after electrolysis,

946
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Budnikova et al.
the black colloidal solution coagulates gradually, and
nickel phosphide including bipyridine precipitates.16
Similar results are observed in the case of the electroꢀ
chemical reduction of the nickel complexes with phen
and PPh3 in the presence of white phosphorus.
It is of interest that in DMF the reduction current of
the nickel(II) complex with white phosphorus almost corꢀ
responds to the current of the initial NiX2L complex,
whereas in MeCN the height of the peak of the [Ni—P4]
complex often increases. This fact indicates an important
role of the solvent in the studied complexation and transꢀ
formation processes involving P4.
calculations18: the P—P bond energies change nonꢀ
uniformly and effective charges appear on the P atoms. It
can be assumed that a similar pattern would be observed
for several other nickel complexes with σꢀdonor ligands
when P4 is incorporated into the coordination sphere of
the metal. The results of quantumꢀchemical calculations
will be considered in more detail elsewhere.
Complexes
Ni(BF4)2(triphos)
in
acetone,
Ni(BF4)2(n2p2) in DMF, and Ni(BF4)2phen and
NiX2(PPh3)3 in MeCN (X = BF4, Br). The dynamics of
slow chemical transformations can be studied by a change
in the morphology of cyclic voltammograms of the NiII
complexes in the presence of P4. When the activation and
transformation of P4 in the coordination sphere of the
NiIIL complex occur easily in the absence of electroꢀ
chemical action, a gradual decrease in the concentration
of the initial NiIIL in solution is detected in the CV. This
process can be caused by a change in the oxidation state
of nickel due to phosphorus oxidation with NiII, which is
accompanied by the appearance of a more cathodic NiIC3
peak (Fig. 4). In the general form, the oxidation of white
phosphorus in the coordination sphere of nickel(II) can
be presented by Scheme 2.
It can be expected that the reduction potential of the
Ni complex determines its reactivity toward white phosꢀ
phorus (as the ligand and substrate) and certain regulariꢀ
ties will be found. We analyzed the dependence of the
shift of the reduction potential of the nickel complex
[NiL—P ]
4
upon white phosphorus addition (∆E = ERed
–
ERed[NiL]) on the reduction potential of the initial nickel
complex. The results are presented in Fig. 3. In several
[NiL]
cases, a satisfactory correlation between ∆E and ERed
is observed. The more negative the reduction potential of
the initial nickel complex (ERed[NiL]), the higher is the
potential shift in the presence of white phosphorus (∆E).
Although there is a certain scatter of points, we can estiꢀ
mate ERed at ∆E = 0 as a value close, in most cases, to
–0.8—–0.9 V. Although this regularity is approximate, it
indicates the determining role of white phosphorus as a
ligand, because its presence aligns the difference in
the redox properties of the initial NiX2Ln complexes.
The preliminary quantumꢀchemical calculations of the
NiIIbpy, Ni0bpy, NiIIbpy—P4, and Ni0bpy—P4 complexes
showed17 that their coordination with white phosphorus
decreases the HOMO energy of the complexes and afꢀ
fects, correspondingly, their reduction potentials, which
shift to less negative values compared to that of NiIIbpy.
The nonpolar P4 molecule is activated due to coordinaꢀ
tion, which is also confirmed by the quantumꢀchemical
Scheme 2
NiX2LS + P4
NiX2(P4)L
Ni+[(P4)+]X2L
The products of the reactions of P4 with NiIItriphos
and NiII(n2p2), which are binuclear NiI complexes with
the cycloꢀP3 ligand (Scheme 3), were isolated in the indiꢀ
vidual state. Their structures were determined by NMR
and ESR spectroscopies, elemental analysis, and cyclic
voltammetry.12
The cyclic voltammograms of complexes 1 and 2 show
reversible reduction corresponding to the NiI/Ni0 redox
transition (see Fig. 4, curve 2).
It is of interest that the reduction potential of the
nickel(II) complexes involved in the transformation of the
P4 molecules without electroreduction lies below the poꢀ
tential region in which the straight lines reflecting the
∆E/V
0.7
3
3
Ni(BF4)2—DMF
NiCl2—DMF
0.6
0.5
0.4
0.3
0.2
0.1
2
2
NiBr2—DMF
C2
C3
NiBr2—acetonitrile
Ni(BF4)2—acetone
3
C1
2
–I
1
1
2
A2
1
3
2
1
1
2
3
1
–E
A3
0.5
1.0
1.5
–ERed/V
A1
Fig. 3. Shifts of the reduction potential of NiIIL upon the addiꢀ
Fig. 4. Schematic cyclic voltammograms of the NiX2L nickel
complex with the σꢀdonor ligand in the absence (1) and presꢀ
ence (2) of white phosphorus (1 : 1) after 1—2 h (at different
ligands).
[NiL—P4]
[NiL]
tion of white phosphorus ∆E = ERed
ferent reduction potentials of the initial nickel complex ERed
– ERed
at difꢀ
[NiL]
:
1, bpy; 2, phen; and 3, PPh3.

Electrochemical activation of white phosphorus
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
947
Scheme 3
(Federal Target Scientific Technical Program "Investigaꢀ
tion and Developments on Priority Directions of Science
and Technology," theme "Highly Reactive Intermediates
in Chemical Reactions"), and the Russian Academy of
Sciences (Complex Programs of the Division of Chemisꢀ
try and Materials Sciences of the Russian Academy of
Sciences Nos 1 and 8).
References
L = triphos (1), n2p2 (2)
1. T. V. Magdesieva and K. P. Butin, Usp. Khim., 2002, 71, 255
[Russ. Chem. Rev., 2002, 71 (Engl. Trans.)].
2. A. E. Shilov and G. B. Shul´pin, Chem. Rev., 1997, 97, 2879.
3. J. Costamagna, G. Ferraudi, B. Matsuhino, M. Camposꢀ
Vallette, J. Canales, M. Villagran, J. Vargas, and M. F.
Aquirre, Coord. Chem. Rev., 2000, 196, 125.
dependence of ∆E on ERed[NiL] converge (see Fig. 3) upon
their extrapolation to ∆E = 0. It can be assumed that this
NiL
potential region is boundary, and at less negative Ep
4. M. Ehses, A. Romerosa, and M. Peruzzini, in Top. Cur.
Chem., 2002, 220, 107.
5. O. J. Scherer, Angew.Chem., 1990, 102, 1137.
6. M. Scheer and E. Herrman, Z. Chem., 1990, 30, 41.
7. H. L. Su, Y. Xie, B. Li, X. M. Liu, and Y. T. Qian, Solid
State Ionics, 1999, 122, 157.
8. Yu. H. Budnikova, J. Perichon, D. G. Yakhvarov, Yu. M.
Kargin, and O. G. Sinyashin, J. Organomet. Chem., 2001,
630, 185.
9. D. G. Yakhvarov, Yu. G. Budnikova, D. I. Tazeev, and
O. G. Sinyashin, Izv. Akad. Nauk, Ser. Khim., 2002, 1903
[Russ. Chem. Bull., Int. Ed., 2002, 51, 2059].
white phosphorus can be transformed in the coordination
sphere of the metal without electricity, i.e., it can spontaꢀ
neously be oxidized to the cycloꢀP3 ligands reducing
NiII to NiI.
Thus, the CV method is convenient for (1) the detecꢀ
tion of white phosphorus coordination with the nickel(II)
complexes by a change in the current and reduction poꢀ
tential of the latter and (2) the study of the innerꢀsphere
interaction between Ni0 and a white phosphorus molꢀ
ecule resulting in P4 transformation with the P—P bond
cleavage.
10. Yu. G. Budnikova, A. G. Kafiyatullina, O. G. Sinyashin,
and R. R. Abdreimova, Izv. Akad. Nauk, Ser. Khim., 2003,
882 [Russ. Chem. Bull., Int. Ed., 2003, 52, 929].
11. R. M. Kuznetsov, A. S. Balueva, I. S. Litvinov, A. T.
Gubaidullin, G. N. Nikonov, A. A. Karasik, and O. G.
Sinyashin, Izv. Akad. Nauk, Ser. Khim., 2002, 142 [Russ.
Chem. Bull., Int. Ed., 2002, 51, 151].
12. Yu. G. Budnikova, A. G. Kafiyatullina, A. S. Balueva, R. M.
Kuznetsov, V. I. Morozov, and O. G. Sinyashin, Izv. Akad.
Nauk, Ser. Khim., 2003, 2289 [Russ. Chem. Bull., Int. Ed.,
2003, 52, 2419].
13. K. P. Butin, V. V. Strelets, and O. A. Reutov, Metalloorg.
Khim., 1990, 3, 814 [J. Organomet. Chem. USSR, 1990, 3
(Engl. Transl.)].
14. G. Bontempelli, F. Magno, and S. Daniele, J. Electroanal.
Chem., 1983, 159, 117.
15. A. A. Pozdeeva, U. M. Dzhemilev, N. R. Popod´ko, R. I.
Khusnutdinov, S. I. Zhdanov, and G. A. Tolstikov,
J. Organomet. Chem., 1989, 367, 205.
16. Yu. H. Budnikova, D. I. Tazeev, B. A. Trofimov, and O. G.
Sinyashin, Electrochem.Commun., 2004, 6, 700.
17. I. Ya. Ogurtsov, V. Mirzac, M. Peruzzini, and Yu. H.
Budnikova, Proc. Int. Conf. "New Approaches in Organomeꢀ
tallic and Coordination Chemistry. Look from 21th Century"
(Nizhny Novgorod, June 1—6, 2002), Nizhny Novgorod,
2002, 126.
Thus, two routes of white phosphorus activation are
possible. The first route is the coordination with metal
resulting in the retention of the structure of the P4 molꢀ
ecule. As a result, the white phosphorus tetrahedron is
only deformed without its destruction. Donorꢀacceptor
interactions between the metal and ligands decrease the
LUMO energy of the complex and, correspondingly, the
reduction potential of NiII. This case is characteristic of
the complexes reducible at high negative potentials
|Ered|> ~0.9 V (L = bpy in DMF, MeCN, and acetone;
phen and PPh3 in DMF and acetone). This complex
should be reduced on the electrode to cleave the P—P
bonds.
The second route is the oxidation of white phosphorus
in the coordination sphere of the NiII complex. This proꢀ
cess occurs when the nickel(II) complex has a suffiꢀ
ciently high oxidizing ability and is rather easily reduced
(~0—0.9 V) (X = BF4, L = triphos in acetone; n2p2 in
DMF; phen and PPh3 in MeCN). This route produces a
new NiI complex, for example, Ni2triphos2(P3)(BF4)2.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 01ꢀ03ꢀ33210
and 04ꢀ03ꢀ32830), the INTAS (Grant 00ꢀ0018), the
Foundation of the President of the Russian Federation
(Grants 01ꢀ15ꢀ99353 and MDꢀ299.2003.03, the Program
for Support of the Leading Scientific Schools, Grant
NSh 1985.2003.3), the Ministry of Industry and Science
18. S. Kang, Th. A. Albright, and J. Silvestre, Croat. Chem. Acta,
1985, 57, 1355.
Received January 30, 2004;
in revised form September 20, 2004