Mendeleev Commun., 2002, 12(5), 175–176
Selective monoarylation of phosphorus trichloride by the electrochemically
generated organonickel σ-complex MesNiBrbpy
Dmitry G. Yakhvarov, Yulia H. Budnikova* and Oleg G. Sinyashin
A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre of the Russian Academy of Sciences,
4
1
0.1070/MC2002v012n05ABEH001632
The use of the electrochemically generated organonickel σ-complex MesNiBrbpy enables the selective monoarylation of phos-
phorus trichloride to be achieved under mild conditions.
The development of ecologically safe and resource-saving chem-
ical and engineering processes has become an important strategic
objective for science and technology. In this context, homo-
geneous catalysis has many attractions, notably in terms of
selectivity and efficiency. For this reason, increasing attention is
being given to the combination of organic electrosynthesis and
catalysis with the participation of various transition metal com-
plexes. So far, highly effective catalytic processes have been
developed1 involving the formation of new carbon–carbon or
carbon–heteroatom bonds using organic and inorganic com-
pounds as precursors. The selective electrosynthesis of specific
organic compounds containing functional groups and chemically
active centres is of particular interest.
MesNiBrbpy in DMF only one reversible one-electronic wave
at –1.80 V was present.
Note that the electrochemically synthesised σ-complex
MesNiBrbpy is an analogue of a Grignard reagent and, con-
sequently, the investigation of its activity in reactions pro-
†
General Procedures. All manipulations and reactions were carried out
in a dry argon atmosphere. All solvents were purified and dried prior
to use. Acetonitrile was purified by triple fractional distillation over
–2
phosphorus anhydride in the presence of KMnO . The concentration of
4
–3
–3
residual water was 10 mol dm . DMF was purified using a published
procedure8 to achieve a residual water content of 0.01–0.005 wt%. The
supporting salts were twice recrystallised (Et NBr from MeCN and
4
Et4NBF4 from ethanol) and dried in a vacuum at 70 °C for two days.
Alcohols were refluxed with BaO for 5 h and then distilled. NiBr bpy
The selective monoarylation of phosphorus trichloride is one
of the key aspects in preparing new organophosphorus ligands
for catalytic systems, since they are useful precursors of various
organophosphorus compounds. The traditional syntheses of
dichloroarylphosphines using Grignard or organolithium reagents
usually do not give high yields and are associated with the need
for severe conditions and flammable media, complicating the
industrial synthesis of this class of compounds and requiring
2
9
was prepared according to the reported method. Preparative electrolysis
1
3
1
at a constant current density, C and H NMR spectroscopy, elemental
analysis and ESR spectroscopy were used to establish the structure and
yields of the electrosynthesis products.
Cyclic voltammograms were recorded at a glassy carbon electrode
with 1.0 mm diameter in a thermostatically controlled cell in an argon
–3
atmosphere. A silver electrode Ag/AgNO3 (0.01 mol dm solution in
MeCN) served as a reference electrode and a platinum wire served as an
3
serious safety measures. Among the dichloroarylphosphines the
auxiliary electrode. The curve was recorded on a PI-50-1 potentiostat.
–
1
phosphines having bulky aromatic fragments [e.g., 2,4,6-tri-
methylphenyl or 2,4,6-tris(tert-butyl)phenyl] occupy a special
place. The mesitylphosphoric derivatives are useful precursors
The scan rate was 50 mV s . Preparative electrolysis was performed
using a B5-49 dc source in a thermostatically controlled cylindrical
3
undivided electrolyser (a three-electrode cell) with 40 cm volume. A
–
3
4
silver electrode Ag/AgNO (0.01 mol dm solution in MeCN) served as
of homo- and heteropolynuclear compounds, and it is known
3
2
a reference electrode. Platinum with a surface area of 20 cm was used
that the greater the steric capacity around the phosphorus atom
in the ligand, the greater the selectivity of the catalytic pro-
as a cathode. A flow of argon was bubbled through the electrolyte in the
course of electrolysis. During electrolysis, the electrolyte was stirred
5
cesses involving the corresponding metal complexes. Apart from
with a magnetic stirrer. A saturated solution of Et NCl in MeCN was
4
the above drawbacks, a characteristic of all bulky dichloroaryl-
phosphines syntheses (e.g., for dichloromesitylphosphine and
similar bulky derivatives) is that there are special difficulties
connected, firstly, with preparing the initial Grignard reagents
used as the anolyte, and the membrane was made from paper.
1
H NMR spectra were obtained in CDCl on a Varian T-60 spectrometer
3
with the working frequency 60 MHz using tetramethylsilane (TMS) as
an internal standard. 31P NMR spectra were recorded using a CXP-100
(
the reaction of MesCl with magnesium metal does not readily
Bruker spectrometer (with 85% H PO as an external standard) both
3
4
proceed using the traditional procedures) and, secondly, MesMgBr
with and without proton decoupling.
undergoes slow reaction with PCl to give a mixture of pro-
Electrochemical synthesis of MesNiBrbpy. The working solution
3
–
4
(
catolyte) was made by dissolving 0.1875 g (5×10 mol) of NiBr bpy,
2
ducts (MesPCl , MesPClBr and MesPBr ) which is difficult to
2
2
–
3
–4
separate.6
,7
1.05 g (5×10 mol) of Et NBr and 0.075 ml (5×10 mol) of MesBr in
4
3
0 ml of DMF. The electrolysis was carried out under potentiostatic
The aim of this study was to consider the possibility of
selectively monoarylating phosphorus trichloride under the action
of the electrochemically synthesised organonickel σ-complex
MesNiBrbpy.
conditions at the working electrode potential –1.52 V (reference electrode:
Ag/0.01 M AgNO in MeCN); 27 mAh of electricity were passed through
3
the electrolyte. After the electrolysis the solvent was evaporated, and the
products were extracted using diethyl ether. The ether was then evaporated
and the product dried in vacuum at 30 °C to give 0.18 g of the σ-complex
2
It is known that the first and limiting stage in the electro-
catalytic dehalogenation process is the oxidative addition of
organic halides to an electrochemically generated complex
MesNiBrbpy (yield 87%).
Mesityl-nickel(II)-bromide-2,2'-bipyridine: mp 149 °C (decomp.). 1H
0
Ni bpy:
NMR (CDCl ) d: 8.56–8.57 (m, 2H, bpy), 8.33–8.37 (d, 2H, bpy), 7.79–
3
7
6
1
.82 (m, 2H, bpy), 7.28–7.31 (m, 2H, bpy), 6.45 (m, 2H, C H ), 2.59 (s,
6 2
II
0
Ni bpy + 2e
Ni bpy
H, Me), 2.17 (s, 3H, Me). Found (%): C, 55.03; H, 4.60; N, 6.03; Ni,
4.16; Br, 18.90. Calc. for C H N NiBr (%): C, 55.14; H, 4.59; N,
0
Ni bpy + RX
RNiXbpy
1
9
19
2
II
6.77; Ni, 14.18; Br, 19.31.
In case of MesBr the electrochemical reduction of Ni bpy to
Synthesis of MesPCl . A solution of 0.2 g (0.5 mmol) of MesNiBrbpy
0
2
Ni bpy in the presence of MesBr leads to the selective forma-
tion of the organonickel σ-complex MesNiBrbpy as the product
of an oxidative addition of MesBr to the electrochemically
in 40 ml of diethyl ether was added to a solution of 0.7 g (5 mmol) of
phosphorus trichloride in 40 ml of diethyl ether at –70 °C (cooling bath
with acetone and liquid nitrogen) with stirring for 10 min. After stirring
for 2 h, the reaction mixture was slowly heated to room temperature. The
ether and the excess of phosphorus trichloride were evaporated, and the
residue was distilled in a vacuum to give 0.07 g of a very viscous liquid
0
generated Ni bpy.
0
Ni bpy + MesBr
MesNiBrbpy
This σ-complex was extracted and characterised by different
physico-chemical methods. In the cyclic voltammogram of
(d31P = +168.35 ppm, bp 47–49 °C/0.1 Torr). The yield of MesPCl
was 68%.
2
†
–
175 –