Nickel-catalysed electrochemical coupling between mono- or di-chlorophenylphosphines and aryl or heteroaryl halides

Article abstract of DOI:10.1016/S0022-328X(98)00963-2

Nickel-catalysed electrochemical cross-coupling between aryl- or heteroaryl-halides and chlorodiphenylphosphine or dichlorophenylphosphine affords tertiary phosphines in good to high yields.

Full text of DOI:10.1016/S0022-328X(98)00963-2

Journal of Organometallic Chemistry 575 (1999) 63–66
Nickel-catalysed electrochemical coupling between mono- or
di-chlorophenylphosphines and aryl or heteroaryl halides
Yulia Budnikova a, Yuri Kargin b, Jean-Yves Ne´de´lec a,*, Jacques Pe´richon a
a Laboratoire d’Electrochimie, Catalyse et Synthe`se Organique (UMR 7582) CNRS-Uni6ersite´ Paris 12-Val de Marne, 2 Rue Henri-Dunant,
F-94320 Thiais, France
b Institute of Organic and Physical Chemistry of RAS, Arbuzo6 street, 8, Kazan 420061, Russia
Received 5 June 1998; received in revised form 20 August 1998
Abstract
Nickel-catalysed electrochemical cross-coupling between aryl- or heteroaryl-halides and chlorodiphenylphosphine or
dichlorophenylphosphine affords tertiary phosphines in good to high yields. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Tertiary phosphines; Electroreductive cross-coupling; Nickel complex catalysis
1. Introduction
Na or K) undergo direct substitution with 2- or 4-
halopyridines and also with aryl halides or sulfonates
which are not reactive with strong nucleophiles. Palla-
dium catalyses the reaction between trimethylstannyl-
diphenylphosphine or trimethylsilyl-diphenylphosphine
and various aromatic halides [2]. Nickel has been used
also to catalyse the formation of BINAP from Ph2PH
and 1,1%-binaphtyltriflate [3]. Recently, the direct cou-
pling between Ph2PCl and various ortho-substituted
aryl triflates or aryl halides has been reported to occur
in good yields in the presence of nickel as catalyst and
zinc as reductant, in DMF at 100–110°C [4].
We have described previously an electrochemical
method of synthesis of alkyl- or benzyl-diphenylphos-
phines by reduction of a mixture of the alkylhalide and
Ph2PCl in DMF or NMP in the presence of a sacrificial
magnesium anode [5]. This electrochemical coupling is
not convenient however for the arylation of
chlorophosphines because the electrogenerated phos-
phide does not react with aryl halides. In the course of
our research on cross-coupling reactions between aryl
Aryl and heteroaryl tertiary phosphines are useful
ligands in homogeneous catalysis. The presence of
phenyl groups substituted with various functionalities is
of great interest to modify the electronic properties of
the ligand and then modulate the reactivity of the
metallic centre associated with it, or to give access to
precursors of hydrosoluble complexes, or to prepare
ligands which can be immobilised easily. Also mixed
aryl-heteroaryl phosphines combining the complexing
properties of the phosphorus atom and of the het-
eroatom, specially nitrogen, can display useful new
properties [1].
The chemical methods involving the reaction between
halophosphines and organometallic reagents are not
convenient to prepare arylphosphines bearing electron-
withdrawing groups. Phosphides (Ph2PM, with M=Li,
* Corresponding author. Tel.: +33-1-49781143; fax: +33-1-
49781148; e-mail: nedelec@glvt-cnrs.fr.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00963-2

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Y. Budniko6a et al. / Journal of Organometallic Chemistry 575 (1999) 63–66
or heteroaryl halides and various halo compounds [6–
8] catalysed by electrogenerated Ni(0) complexes we
have investigated also the reactions involving Ph2PCl
and PhPCl2 reported here (Eq. (1)).
−1.1 and −1.5 V/SCE; this indicates that the coupling
may not require the reduction of |-arylnickel(II) into
|-arylnickel(I). Indeed, we have shown that a |-aryl-
(1)
nickel(II)–bpy complex reacts rapidly with Ph2PCl in
the following experiment: a stable |-arylnickel(II) com-
plex can be obtained by electroreduction of NiBr2bpy
in DMF in the presence of ortho-substituted phenyl
bromides like o-bromotoluene; on the addition of
Ph2PCl (one equivalent) the red colour typical for
|-arylnickel(II)bpy quite rapidly turned into the green
of NiX2bpy, and the tertiary phosphine was obtained.
We cannot, however, exclude the occurrence, at the
high current intensity (0.2–0.5 A) used in this process,
of the formation of arylNi(I)bpy and its reaction with
the chlorophosphine. These two routes are shown on
Scheme 1.
In the same reaction conditions, the use of PCl3 in
place of Ph2PCl or PhPCl2 and PhBr or PhI led to the
formation of PPh3 but in quite a low yield and only at
the beginning of the electrolysis. We first thought of a
possible side reaction of PCl3 with DMF and we thus
used acetonitrile as the solvent, but we obtained the
same results. PCl3 is probably two reactive towards the
electrogenerated zerovalent nickel and the species
derived do not react with the aromatic halides.
This methodology offers a simple and efficient ap-
proach to the preparation of various tertiary phosphi-
nes. It can be a useful alternative to the chemical
procedure reported in Ref. [4] as it does not rely on the
reactivity of zinc powder, and can be controlled more
easily in large scale experiments than procedures using
reactive metals.
2. Results and discussion
We have reported previously on the efficient elec-
troreductive coupling of arylhalides [6] or of halothio-
phenes [7] with h-halo-esters or -ketones in the presence
of Ni-2,2%-bypiridine (bpy) as a catalyst and a sacrificial
anode. We have used the same procedure for the elec-
trochemical synthesis of tertiary phosphines. The reac-
tions were carried out in an undivided electrolysis cell
flushed with argon and fitted with a magnesium rod as
the anode and a nickel foam as the cathode, at room
temperature under a constant current intensity of 0.2–
0.5 A. The aryl or heteroaryl halide (one equivalent)
and NiBr2bpy (0.1 equivalent) were added to a solution
of DMF containing NBu4BF4 as the supporting elec-
trolyte. Ph2PCl or PhPCl2 was added portionwise, i.e.
0.1 equivalents of Ph2PCl, or 0.05 equivalents of
PPhCl2, for every 0.2 Faraday passed per mole of ArX,
until the concentration of the tertiary phosphine, as
determined by GC analysis, was constant, which
amounted to 0.5–0.75 equivalents of Ph2PCl and 0.2–
0.3 equivalents of PhPCl2. When the reaction was con-
ducted with a stoichiometric mixture of the aryl halide
and Ph2PCl, no cross-coupling occurred; Ph2PCl was
converted into Ph2PH and Ph2PPPh2 due to the faster
reaction of the chlorophosphine with Ni(0) as com-
pared with most aryl halides.
Results are reported in Table 1. In most cases moder-
ate to good yields of tertiary phosphines were obtained
and this simple method is notably very convenient to
prepare various tertiary phosphines containing het-
eroaryl groups (Table 1, entries 9, 10, 11, 12, 14, 15), or
aryl groups bearing electronwithdrawing substituents
(Table 1, entries 6, 7, 8). For these last compounds the
use of a zinc sacrificial anode gave better results than a
magnesium one. The presence of zinc ions generated by
the oxidation of the anode buffers the potential of the
solution at a value higher than for the reduction of the
arylhalide. The main side products are a reduction of
the aryl halide and the chlorophosphine.
3. Experimental
The single-compartment cell was fitted with a rod of
magnesium or zinc as the anode, surrounded by a
cylindrical nickel grid as the cathode. To the solution of
Bu4NBF4 (0.5 mmol), NiBr2bpy (1 mmol), the aryl or
heteroarylhalide (15 mmol) in DMF (40 ml) was added
dropwise the appropriate phosphine at a rate of 1 mol
of Ph2PCl per 2 F of electricity or 1 mol of PhPCl2 per
4 F of electricity while a current of 0.5 A was applied
until ArX was consumed. The solution was then hy-
drolysed using 0.1 N NH4Cl and extracted with Et2O.
The organic layers were washed with H2O, dried, and
the solvent was evaporated. The products were purified
by column chromatography on silica gel with pentane/
Et2O mixtures as the eluents. Most tertiary phosphines
are known, and they were characterised on the basis of
In our previous studies on the coupling reactions
between aryl halides and activated halides [6,7] or 2-
halo-pyridine [8] we have shown that the coupling
occurs via a |-arylnickel(I) complex formed by elec-
troreduction of |-arylnickel(II) obtained first by oxida-
tive addition of the aryl halide to the electrogenerated
zerovalent nickel. For the electrosynthesis of the ter-
tiary phosphines the cathode potential was between

Y. Budniko6a et al. / Journal of Organometallic Chemistry 575 (1999) 63–66
65
Table 1
Nickel-catalyzed electrochemical coupling of aryl or heteroaryl halides and chlorophosphines
Entry
1
PhnPCl3−n
Ph2PCl
ArX
Product
Yield %a
87
PhBr
1
2
2
2-BrC6H4CH3
54
3
4-BrC6H4CH3
3
56
4
5
6
7
4-CH3O–C4H5Br
4-Me2N–C6H4Br
4-CO2Et–C6H4Br
3-CO2Et–C6H4Br
4
5
6
7
52
70
63b
66b
8
9
2-Cl–C5H4N
3-Cl–C5H4N
8
9
80
63
10
11
2-Cl–C4H3S
10
11
65
66
2-Cl–6-CH3O–C5H3N
12
13
2-Cl–C4H3N2
3-CN–C6H4Br
12
13
50
45b
14
14
25
15
16
PhPCl2
PhBr
1
72
68
2-Cl–C5H4N
15
a Experimental conditions: see text; isolate yields % vs chlorophosphine.
b Anode of Zn.

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Y. Budniko6a et al. / Journal of Organometallic Chemistry 575 (1999) 63–66
Scheme 1.
spectroscopic data and melting point by comparison to
1.23 (t, 3H, J=7.5 Hz); 31P-NMR (81 MHz,CDCl3):
−7.0; m.p. 100–101°C. Anal. Calc. for C2lH19PO2: C,
75.45; H, 5.69; P, 9.28; Found: C, 75.60; H, 5.80; P,
9.31.
literature data. Compounds 6, 7, and 12 are new.
1
Product analysis: H- and 13C-NMR (ref. TMS), and
31P-NMR (ref. 85% H3PO4) were recorded on an AC
200 Bruker spectrometer; GC-MS spectra were
recorded on a Finnigan ITD 800 spectrometer.
3.3. 2-diphenylphosphinopyrimidine 12
Mass., m/z (rel. intensity): 264 (M+, 100); 184(27),
107(28); 13C-NMR (50 Mhz, CDCl3): 156.49 (d, J=7
Hz), 134.58 (d, J=20 Hz), 129.24; 128.52; 128.37;
3.1. (4-Ethoxycarbonylphenyl)diphenylphosphine 6
Mass., m/z (rel. intensity): 334 (M+, 100); 306 (9);
183 (22); 152 (6); 107 (8); 77 (5); 13C NMR (50 MHz,
CDCl3): 166.17; 143.70 (d, J=14.9 Hz, C–P); 136.05
(d, J=10.7 Hz); 133.97; 133.57; 133.17; 132.77; 131.77;
130.22; 129.17; 129.03; 128.95; 128.58; 128.43; 60.84;
14.16; 1H-NMR (200 MHz, CDCl3): 7.19–7.34 (m,
10H); 7.43 (d, 2H), 7.77 (d, 2H), 4.25 (q, 2H, J=21.5
Hz); 1.27 (t, 3H, J=14.3 Hz); 31P-NMR (81 MHz,
CDCl3): −6.7; m.p. 99–100°C. Anal. Calc. for
C2lHl9PO2: C, 75.45; H, 5.69; P, 9.28; Found: C, 75.34;
H, 5.93; P, 9.28.
1
118.81; H-NMR (200 Mhz, CDCl3): 8.59 (d, 2H, J=
4.87 Hz), 7.26–7.48 (m, 10H); 6.98–7.03 (m, 1H);
31P-NMR (81 MHz, CDCl3): −0.2; m.p. 118–119°C.
Anal. Calc. for C16H13N2P: C, 72.73; H, 4.92; P,11.74;
N, 10.61; Found: C, 72.65; H, 4.98; P, 11.61;N, 10.21.
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