Anthony KERMAGORET - THESES ET MEMOIRES DE L'UDS

Ph 2
P
N
Ni
17
Cl
Cl
Cl
N
Ni
PPh 2
Cl
Cl
18
Ph 2P
Ni
Cl
N
Chapitre IV
The complexation of NiCl2 by ligand 14 in methanol led to cleavage of the phosphinite P-O
bond and substituent exchange at the phosphorus to form [Ni(µ-Cl)2(2-pyridine ethanol)2]Cl2
19 and [NiCl2(PPh2OMe)2] (eq 2). The very low solubility of 19 in CH2Cl2 facilitated
separation of the Ni(II) complexes. This reaction is consistent with the sensitivity of
phosphonites to the presence of alcohols, 58 and the breaking of the P-O bond does not
necessarily requires the presence of a metal cation. Complex 19 has been obtained directly
from (pyridin-2-yl)methanol and NiCl2 and was shown by X-ray diffraction to have a
dinuclear structure. 59
4
14
O
N
PPh 2
+ 4 NiCl 2
MeOH
N
N
OH
Ni
OH
Cl
Cl
19
+
HO
Ni
HO
2 NiCl 2(PPh 2OMe) 2
The use of methanol for metal complexation with phosphinites 14 or 16 and phosphonite 15
should therefore be avoided but other solvents (MeCN, THF or CH2Cl2) led to poor yields
owing to the very low solubility of NiCl2. However, reaction of [NiCl2(DME)] or
[NiBr2(DME)] in CH2Cl2 with 14-16 led to the high yield formation of the Ni(II) complexes
20-23, respectively (up to 92%). Their colors in the solid state are respectively grey, green,
red or maroon but all complexes afforded red CH2Cl2 solutions. Red single crystals of 22
suitable for X-ray diffraction were obtained by slow diffusion of pentane into a solution of
the complex in chlorobenzene and 22 presented a mononuclear structure (see below).
O
N Ni
PPh 2
X
X
20 X = Cl
21 X = Br
O
N Ni
P(t-Bu) 2
Cl
Cl
O P
N
22 23
N
N
O
Ni
Cl
Cl
2+
2 Cl -
(2)
7