Reactions of activated organonickel σ-complexes with elemental (white) phosphorus

Article abstract of DOI:10.1007/s11172-013-0358-9

The reactivity of organonickel σ-complexes of the type [NiBr(Ar)(bpy)] (Ar is 2,4,6-tri-methylphenyl (Mes) or 2,4,6-triisopropylphenyl (Tipp); bpy is 2,2′-bipyridine) toward elemental (white) phosphorus was studied. For the reaction to occur, the complexe

Full text of DOI:10.1007/s11172-013-0358-9

Russian Chemical Bulletin, International Edition, Vol. 62, No. 11, pp. 2472—2476, November, 2013
2472
Reactions of activated organonickel ꢀcomplexes
with elemental (white) phosphorus*
D. G. Yakhvarov,a,b S. V. Kvashennikova,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. Eꢀmail: yakhvar@iopc.ru
bKazan Federal University,
18 ul. Kremlyovskaya, 420008 Kazan, Russian Federation
The reactivity of organonickel ꢀcomplexes of the type [NiBr(Ar)(bpy)] (Ar is 2,4,6ꢀtriꢀ
methylphenyl (Mes) or 2,4,6ꢀtriisopropylphenyl (Tipp); bpy is 2,2´ꢀbipyridine) toward eleꢀ
mental (white) phosphorus was studied. For the reaction to occur, the complexes must be
activated by removal of the bromide anion from the coordination sphere of nickel. This can be
achieved either in the presence of halogen scavengers or by electrochemical reduction. The
arylphosphinic acids ArP(O)(OH)H formed by hydrolysis of organic nickel phosphides are the
major reaction products of the overall process.
Key words: arylphosphinic acids, white phosphorus, organonickel ꢀcomplexes, organic
phosphides, electrochemical activation.
Organometallic ꢀcomplexes (i.e., compounds conꢀ
taining a metal—carbon ꢀbond) are key intermediates in
various catalytic processes involving organic and organoꢀ
element compounds.1—5 Compounds of this class are also
formed in electrocatalytic reactions of organic halides with
complexes of transition metals such as nickel, palladium,
and some6—9 other Period IV metals. At this point, howꢀ
ever, the world scientific literature provides limited data
on the properties and reactivities of organonickel ꢀcomꢀ
plexes formed in homoꢀ and crossꢀcoupling of organic
halides, chlorophosphines, and white phosphorus. Moreꢀ
over, while the basics of the electrochemical phosphorylaꢀ
tion of organic halides with white phosphorus under elecꢀ
trocatalytic conditions in the presence of nickel complexꢀ
es have been already developed, the mechanism of activaꢀ
tion and transformation of the P4 tetrahedron as well as
the mechanism of P—C bond formation remain poorly
understood. It should be noted that known techniques for
the synthesis of organophosphorus compounds from eleꢀ
mental (white) phosphorus are based on powerꢀconsumꢀ
ing and environmentally unsafe "chlorine" procedures inꢀ
volving the formation of phosphorus acid chlorides and
large amounts of toxic compounds (HCl, POCl3, PCl5,
etc.).10,11 The use of transition metal complexes12,13 and
electrochemical methods14,15 offers an alternative to the
existing routes to organophosphorus compounds.
The goal of the present work was to study the reactivity
of organonickel ꢀcomplexes formed in electrocatalytic
dehalogenation of organic halides in the presence of
nickel complexes with 2,2´ꢀbipyridine toward elemental
(white) phosphorus.
Results and Discussion
We employed the organonickel ꢀcomplexes
[NiBr(Ar)(bpy)]16—18 (Ar is 2,4,6ꢀtrimethylphenyl (Mes) (1)
and 2,4,6ꢀtriisopropylphenyl (Tipp) (2); bpy is 2,2´ꢀbiꢀ
pyridine) as model compounds in reactions with white
phosphorus (Scheme 1). Note that the use of organonickel
ꢀcomplexes containing an unsubstituted phenyl group is
not possible due to they low stability.
Direct reactions of organonickel complexes 1 and 2
with white phosphorus were carried out by mixing a soluꢀ
tion of either complex with a solution of white phosphoꢀ
rus in different solvents (DMF, benzene, toluene, and
THF). However, we found that organonickel ꢀcomplexꢀ
es are absolutely inert to the P4 molecule. No reacꢀ
tion occurred when the resulting mixtures were stirred
at room temperature or at 60 C. A 31P NMR study of
the mixtures revealed that a white phosphorus moleꢀ
cule cannot coordinate to the metal center or displace
the ligands from organonickel ꢀcomplexes 1 and 2.
Moreover, no products resulting from the coordination
or transformation of the P4 molecule were detected
(31P NMR data).
* Dedicated to Academician of the Russian Academy of Sciences
M. P. Egorov on the occasion of his 60th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2472—2476, Novemer, 2013.
1066ꢀ5285/13/6211ꢀ2472 © 2013 Springer Science+Business Media, Inc.

Reactions of organonickel ꢀcomplexes with P4
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013 2473
1
Scheme 1
natant sample shows a weak signal at  –87.9 (d, JPH
=
= 233 Hz) corresponding to the secondary phosphine
Mes2PH. This suggests that white phosphorus tetrahedron
undergoes opening to form a P—C bond. Note that the
primary phosphine MesPH2, which is also formed, has the
stronger ability to coordinate with transition metals because
of its less pronounced (compared to Mes2PH) steric effects
and is completely bound in nickel phosphide complexes,
so free MesPH2 is not detected in the 31P NMR spectrum.
Stirring of the reaction mixture with a small amount
of degassed water for 6 h does not make changes in the
31P NMR spectrum. Addition of a small amount of conꢀ
centrated HCl (37% w/w) was also not effective. However,
paramagnetic nickel(II) can be detected in the solution
after five days, which is reflected in the morphology of the
31P NMR spectrum. As a result, the sixthꢀday spectrum
contains two very broad signals at  6.2 and 22.9. Subseꢀ
quent concentration of the reaction mixture and extracꢀ
tion of organophosphorus products with toluene gave mesꢀ
itylphosphinic acid (MesP(O)(OH)H) as a major reaction
product in moderate yield (32%).
It should be noted that the precipitate containing inꢀ
soluble nickel complexes can be dissolved by addition of
concentrated HNO3. This procedure allows recovering the
major part of nickel involved in the reaction.
A similar reaction procedure with complex 2 gave
2,4,6ꢀtriisopropylphenylphosphinic acid (TippP(O)(OH)H),
though in a lower yield (24%). The secondary phosphine
Tipp2PH was not detected in the reaction mixture. Apparꢀ
ently, its formation is limited by steric hindrances, which
make it difficult to attach a second sterically hindered
aromatic fragment to the phosphorus atom during the
opening of the P4 tetrahedron.
The aforesaid behavior of organonickel ꢀcomplexes
can be associated with the absence of vacant coordination
site at the Ni atom for the P4 molecule to be coordinated
(this usually occurs in the coordination spheres of metal
complexes19—21).
To obtain coordinatively unsaturated organonickel
ꢀcomplexes, we removed the bromide anion from the
coordination sphere in a reaction with thallium hexaꢀ
fluorophosphate. It should be noted that the use of silver
salts as halogen scavengers is not possible under the chosen
conditions because Ag+ ions react with DMF and white
phosphorus to give various polyphosphorus oligomers.
When solid TlPF6 is added to a solution of white phosꢀ
phorus and nickel complex 1, the originally red (due to
[NiBr(Mes)(bpy)]) reaction mixture turns orangeꢀyellow.
This color is characteristic of oligophosphorus intermediꢀ
ates formed by transformations of the coordinated P4 molꢀ
ecule (complex 3) in the coordination sphere of nickel
(Scheme 2).
To obtain reactive species from organonickel ꢀcomꢀ
plexes without using toxic thallium salts as halogen scavꢀ
engers, we applied electrochemical activation. Klein et al.23
have demonstrated, with the organonickel ꢀcomplex
[NiBr(Mes)(bpy)] as an example, that transfer of an elecꢀ
tron to the complex molecule is accompanied by eliminaꢀ
tion of the bromide anion from the coordination sphere of
nickel, thus producing coordinatively unsaturated neutral
complex radical 4 (Scheme 3).
Scheme 2
Scheme 3
The reaction mixture contains only residual amounts
of white phosphorus (31P NMR,  525.8). Upon 24ꢀh stirꢀ
ring, the reaction mixture turns black and, in agreement
with published data22 on activation of nickel bromide comꢀ
plexes, a large amount of TlBr is formed as a colorless
crystalline precipitate (the bromide anions are bound to
the thallium cations). The 31P NMR spectrum of a superꢀ
The sign " " stands for a vacant coordination site.

2474
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013
Yakhvarov et al.
Table 1. Peak potentials* and currents on the cyclic voltammograms of organonickel ꢀcomplexes 1
and 2 at glassy carbon electrode (cathodic potential scan)
Complex
Reduction peaks
Reoxidation peaks
Peak
–E/V
I/A
Peak
–E/V
I/A
[NiBr(Mes)(bpy)] (1)
[NiBr(Tipp)(bpy)] (2)
C1
C2
C3
1.80
2.15
2.62
4.8
4.7
0.4
A1
A2
A3
1.64
2.05
2.50
1.2
4.6
0.4
C1
C2
C3
1.75
2.03
2.33
5.9
2.0
1.3
A1
A2
A3
1.54
1.97
2.20
0.6
4.2
1.0
* The CV curves were recorded without IRꢀcompensation; the potentials are given versus the referꢀ
ence electrode Ag/AgNO3, 0.01 M in MeCN (E(Fc/Fc+) = 0.20 V).
Scheme 4
Following this approach, we tried to activate organoꢀ
nickel ꢀcomplexes 1 and 2 for the preparation of organoꢀ
metallic species that would be reactive toward a white
phosphorus molecule. We found that electron transfer to
the molecules of organonickel complexes 1 and 2 producꢀ
es reactive species capable of transforming a white phosꢀ
phorus molecule into organic nickel phosphides. Note that
the organonickel ꢀcomplexes can be activated in situ in
the presence of white phosphorus because the first cathodꢀ
ic reduction potentials C1 of the organonickel ꢀcomplexꢀ
es (Table 1) are less negative than the electrochemical
reduction of P4 molecule (E = –2.25 V (vs. Ag/AgNO3,
0.01 M in MeCN).15,16
Electrochemical activation of organonickel ꢀcomꢀ
plexes 1 and 2 was carried out in a divided electrochemical
cell in DMF in the presence of 0.1 M Bu4NBF4 as a supꢀ
porting electrolyte. After an electricity quantity of 1 F
(1 e per Ni atom) was passed through the working solution, its
originally red color turned black. This was accompanied
by the formation of black precipitate of organic nickel
phosphides. The 31P NMR spectrum of the supernatant is
featureless, thus suggesting that the consumed phosphoꢀ
rus and derived phosphorusꢀcontaining products are bound
in organic phosphides. After vigorous stirring of the reacꢀ
tion mixture for 6 h, its 31P NMR spectrum shows a signal
at  –87.5 (d, 1JPH = 233 Hz) for the secondary phosphine
Mes2PH. The 31P NMR spectrum of the reaction mixture
obtained from organonickel complex 2 under the same
electrochemical conditions bears no evidence for the presꢀ
ence of a secondary phosphine. This nicely fits the data we
obtained with TlPF6 as a halogen scavenger.
Interestingly, when the organonickel ꢀcomplexes are
activated in the absence of white phosphorus, coordinaꢀ
tively unsaturated intermediate organonickel ꢀcomplexꢀ
es dimerize to give diꢀ and polynuclear organometallic
compounds and clusters. Our investigations of their strucꢀ
tures are in progress.
To sum up, we experimentally proved that the reacꢀ
tions of coordinatively unsaturated organonickel ꢀcomꢀ
plexes with white phosphorus yield organophosphorus
compounds, viz., the arylphosphinic acids ArP(O)(OH)H,
which can be widely used in magnetochemistry as effiꢀ
cient exchange channels24 for novel electronic devices
based on molecular magnetics.
Experimental
Acid hydrolysis and concentration of the resulting
reaction mixtures followed by extraction of the electrolyꢀ
sis products with toluene gave mesitylphosphinic and
2,4,6ꢀtriisopropylphenylphosphinic acids in moderate
yields (53 and 42%, respectively). This confirms that
the P—C bond formation under electrochemical condiꢀ
tions involves the reactions of the activated organonickel
ꢀcomplexes with white phosphorus (Scheme 4).
All experiments were carried out under dry nitrogen using
standard Schlenk equipment. Solvents were purified by distillaꢀ
tion prior to use. Dimethylformamide was purified by threefold
vacuum distillation with intervening desiccation over calcined
K2CO3 and molecular sieves. White phosphorus was treated with
a solution of K2Cr2O7 in conc. H2SO4 and recrystallized from
DMF; then phosphorus was melted (50 C), rolled into beads
while stirring it with a magnetic bar, and cooled. The complexes

Reactions of organonickel ꢀcomplexes with P4
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013 2475
[NiBr(Mes)(bpy)] and [NiBr(Tipp)(bpy)] were prepared as deꢀ
scribed earlier.16,17 The salt Bu4NBF4 (Acros Organics) used as
a supporting electrolyte and TlPF6 (Alfa Aesar) were used as
purchased.
tric current (I = 26.8 mA, electrolysis time 1 h) was passed at the
working electrode potential varying from –1.6 to –1.8 V (vs. Ag/
AgNO3, 0.01 M in MeCN). After the electrolysis was completꢀ
ed, the resulting suspension was treated with 2 M HCl (10 mL)
and the reaction mixture was stirred at room temperature for
120 h and concentrated. The organophosphorus products were
extracted with toluene (3×50 mL) and recrystallized. The yields
of mesitylphosphinic (MesP(O)(OH)H) and 2,4,6ꢀtriisopropylꢀ
phenylphosphinic acids (TippP(O)(OH)H) were 0.098 (53%)
and 0.112 g (42%). Their physicochemical characteristics are in
full agreement with the literature data.24,25
For CV measurements, a stationary glassy carbon disk elecꢀ
trode (active surface area 3.14 mm2) was used as a working elecꢀ
trode. Cyclic voltammograms were recorded on an Epsilon Elecꢀ
trochemical Workstation analytical unit (BASi, USA) in a temꢀ
peratureꢀcontrolled (20 C) threeꢀelectrode cell (linear scan rate
50 mV s–1) in DMF with 0.1 M Bu4NBF4 as a supporting elecꢀ
trolyte. The system Ag/AgNO3, 0.01 M in MeCN (E(Fc/Fc+) =
= 0.20 V) served as a reference electrode. A platinum wire 1 mm
in diameter was used as an auxiliary electrode. The concentraꢀ
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 09ꢀ03ꢀ00933ꢀa
and 12ꢀ03ꢀ97067ꢀr_povolzh´e_a).
D. G. Yakhvarov is grateful to the German Research
Society (DFG, Project RE 771/4ꢀ1), the German Acaꢀ
demic Exchange Service (DAAD, Project A/13/71281),
and the Government of the Tatarstan Republic (the Proꢀ
gram "Algarysh") for financial support of his scientific stay
at the Leibniz Institute for SolidꢀState and Materials
Research (Dresden, Germany).
tion of the substrate was 5•10–3 mol L–1
.
Preparative electrolyses were carried out under potentiostatꢀ
ic conditions using a B5ꢀ71/1 U dc power supply. The potential
of the working electrode (cathode) was measured with a Shch50ꢀ1 dc
voltmeter versus the reference electrode Ag/AgNO3, 0.01 M in
MeCN (E(Fc/Fc+) = 0.20 V). The working surface of the cathꢀ
ode (glassy carbon, Pt) was 32 cm2. After the electrolysis was
completed, the resulting solution was concentrated and organoꢀ
phosphorus products were extracted with toluene and dried
in vacuo at room temperature for 3 h.
31P NMR spectra were recorded on a highꢀresolution Avance
400 spectrometer (Bruker, 161.9 MHz) in DMF at room temꢀ
perature. IR spectra (KBr pellets) were recorded on a Vectorꢀ22
spectrometer (Bruker) in the 4000—400 cm–1 range (resolution
4 cm–1). A GCꢀMS study (EI, 70 eV, ion source temperature
290 C) was carried out on a DFS Thermo Electron Corporation
instrument (Germany). The GC facilities included an IDꢀBP5X
capillary column (50 m × 0.32 mm × 0.25 m; an analog of
DBꢀ5MS) and helium as a carrier gas. The data obtained were
processed with the Xcalibur program. Test samples (the starting
compounds) were infused into the instrument as solutions
(~10–3 g L–1) in HPLCꢀgrade acetonitrile.
Reactions of the complexes [NiBr(Ar)(bpy)] with white phosꢀ
phorus in the presence of TlPF6 (general procedure). Thallium
hexafluorophosphate (0.349 g, 1.0 mmol) was added to a vigorꢀ
ously stirred solution of an organonickel ꢀcomplex (1.0 mmol,
0.414 (1) or 0.498 g (2)) and white phosphorus (0.124 g) in DMF
(40 mL). The originally red (due to the starting organonickel
complex) reaction mixture turned orangeꢀyellow. This was acꢀ
companied by the formation of white precipitate of TlBr. The
resulting suspension was treated with 2 M HCl (10 mL), and
the reaction mixture was stirred at room temperature for 120 h.
The precipitate was filtered off, the filtrate was concentrated,
and organophosphorus products were extracted with toluene
(3×50 mL) and recrystallized. The yields of mesitylphosphinic
(MesP(O)(OH)H) and 2,4,6ꢀtriisopropylphenylphosphinic acꢀ
ids (TippP(O)(OH)H) were 0.059 (32%) and 0.064 g (24%),
respectively. Their physicochemical characteristics are in full
agreement with the literature data.24,25
References
1. Y. Tamaru, Modern Organonickel Chemistry, WileyꢀVCH Verꢀ
lag, Weinheim, 2005, 327 pp.
2. J. Cámpora, Nickel—Carbon ꢀBonded Complexes, in Comꢀ
prehensive Organometallic Chemistry III, Elsevier, Amsterꢀ
dam—Boston, 2007, 8, p. 27.
3. P. W. Jolly, G. Wilke, The Organic Chemistry of Nickel, Acaꢀ
demic Press, London—New York, 1975, Vol. 2, p. 94.
4. G. P. Chiusoli, P. M. Maitlis, Metal Catalysis in Industrial
Organic Processes, RSC Press, Cambridge, 2006, p. 290.
5. I. P. Beletskaya, L. M. Kustov, Russ. Chem. Rev., 2010,
79, 441.
6. Yu. H. Budnikova, Russ. Chem. Rev., 2002, 71, 111.
7. J.ꢀY. Nedelec, J. Perichon, M. Troupel, Organic Electroꢀ
reductive Coupling Reactions using Transition Metal Comꢀ
plexes as Catalysts, in Topics in Current Chemistry, Ed.
E. Steckhan, Springer Verlag, Berlin—Heidelberg, 1997,
Vol. 185, p. 141.
8. T. V. Magdesieva, Elektrokhimiya metalloorganicheskikh soꢀ
edinenii
i metallokompleksov [The Electrochemistry of
Organometallic Compounds and Metal Complexes], in
Elektrokhimiya organicheskikh soedinenii v nachale XXI veka
[The Electrochemistry of Organic Compounds in the Early
XXI Century], Eds V. P. Gul´tyai, A. G. Krivenko, A. P.
Tomilov, Kompaniya Sputnik+, Moscow, 2008, p. 250
(in Russian).
Electrochemical reactions of the complexes [NiBr(Ar)(bpy)]
with white phosphorus (general procedure). A working solution
for electrolysis was prepared by dissolving an organonickel
ꢀcomplex (1.0 mmol, 0.414 (1) or 0.498 g (2)), white phosphoꢀ
rus (0.124 g, 1.0 mmol), and Bu4NBF4 (0.987 g, 3.0 mmol) in
DMF (30 mL). The resulting solution was placed in the cathodic
compartment of a divided cell. The anodic compartment was
charged with a 0.1 M solution (10 mL) of Bu4NBF4 in DMF.
Then a constant voltage was applied to this system, and an elecꢀ
9. H. Lund, J. Electrochem. Soc., 2002, 149, No. 4, S21.
10. Technology Vision 2020. The U.S. Chemical Industry,
ACS Publisher, Washington, 1996, 75 pp.; http://
www1.eere.energy.gov/manufacturing/resources/chemicals/
pdfs/chem_vision.pdf.
11. Studies in Inorganic Chemistry, Vol. 20: Phosphorus. An Outꢀ
line of Its Chemistry, Biochemistry and Uses, 5th ed., Ed. D.
E. C. Corbridge, Elsevier, Amsterdam—Lausanne—New
York—Oxford—Shannon—Tokyo, 1995, 1208 pp.

2476
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 11, November, 2013
Yakhvarov et al.
12. V. A. Milyukov, Yu. H. Budnikova, O. G. Sinyashin, Russ.
Chem. Rev., 2005, 74, 781.
20. B. M. Cossairt, N. A. Piro, C. C. Cummins, Chem. Rev.,
2010, 110, 4164.
13. M. Peruzzini, L. Gonsalvi, A. Romerosa, Chem. Soc. Rev.,
2005, 34, 1038.
14. Yu. H. Budnikova, D. G. Yakhvarov, O. G. Sinyashin,
J. Organomet. Chem., 2005, 690, 2416.
21. M. Scheer, G. Balazs, A. Seitz, Chem. Rev., 2010, 110, 4236.
22. P. Butti, PhD Thesis, ETH Zürich, 2009, 238 pp.
23. A. Klein, A. Kaiser, B. Sarkar, M. Wanner, J. Fiedler, Eur.
J. Inorg. Chem., 2007, 965.
15. D. G. Yakhvarov, E. V. Gorbachuk, R. M. Kagirov, O. G.
Sinyashin, Russ. Chem. Bull. (Int. Ed.), 2012, 61, 1300 [Izv.
Akad. Nauk, Ser. Khim., 2012, 1285].
16. D. G. Yakhvarov, E. A. Trofimova, I. Kh. Rizvanov, O. S.
Fomina, O. G. Sinyashin, Elektrokhimiya, 2011, 47, 1180
[Russ. J. Electrochem. (Engl. Transl.), 2011, 47, 1100].
17. RF Pat. 2396375; Byull. Izobret. [Bulletin of Inventions], 2010,
No. 22 (in Russian); http://www.fips.ru.
24. D. Yakhvarov, E. Trofimova, O. Sinyashin, O. Kataeva,
P. Lönnecke, E. HeyꢀHawkins, A. Petr, Yu. Krupskaya,
V. Kataev, R. Klingeler, B. Büchner, Inorg. Chem., 2011,
50, 4553.
25. G. Keglevich, K. Ludanyi, L. D. Quin, Heteroat. Chem.,
1997, 8, 135.
18. RF Pat. 85903; Byull. Izobret. [Bulletin of Inventions], 2009,
No. 23 (in Russian); http://www.fips.ru.
19. M. Caporali, L. Gonsalvi, A. Rossin, M. Peruzzini, Chem.
Rev., 2010, 110, 4178.
Received June 6, 2013;
in revised form September 18, 2013