Anthony KERMAGORET - THESES ET MEMOIRES DE L'UDS

12
PPh 2
N
O
N
PPh 2
O
N
13
P
14 15
N
O
PPh 2
Chapitre IV
For the synthesis of 2-methyl-oxy-(di-tert-butylphosphino) pyridine 16, 2-(pyridine)ethanol
had first to be deprotonated and reacted with di-tert-butyl(chloro)phosphine (eq 1), because
the phosphine is not electrophilic enough to react directly with a pyridine-alcohol owing to
the electron donor effect of the two tert-butyl substituents.
OH
N
+ n-BuLi
- n-BuH
Li
O
N
+ P(t-Bu) 2Cl
- LiCl
16
O
N
P(t-Bu) 2
All the ligands have been characterized by 1 H, 13 C{ 1 H}, 31 P{ 1 H}, COSY, HMBC and HMQC
NMR spectroscopy. We note the high 31 P{ 1 H} chemical shifts of 16 (δ 166.3 ppm) compared
to that of the phosphinite 14 (δ 117.7 ppm) which results from the steric effect of the tert-
butyl substituents.
2.2 Synthesis of the Ni(II) complexes
To examine the possible influence of the nature of the spacer link between the P and
N donor atoms, we compared ligand 13, which contains a CH2-CH2 spacer, with 14 and 16
which have a isosteric CH2-O spacer. The Ni(II) phosphinopyridine complexes 17 and 18
were prepared by reaction of one equivalent of the corresponding phosphine with NiCl2 in
methanol. The immediate color change, from green to red, indicated a fast reaction. After
work-up, grey and green powders of 17 and 18 were obtained in 83% and 80% yields,
respectively. Slow diffusion of pentane into a CH2Cl2 solution of 18 afforded single crystals
suitable for X-ray diffraction, which established its dinuclear structure (see below). A red-
violet complex has been reported from the reaction of 13 with NiCl2 in refluxing n-butanol. 57
(1)
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