Anthony KERMAGORET - THESES ET MEMOIRES DE L'UDS

Chapitre VI
bulky phosphorus substituents tend to retard chain transfer and produce high molecular
weight polyethylenes. 50,51
R 2
P
O
H
Ni
R = Ph, Cy
SbF 6
Ph
R R'
P
O
M
B(Ar F) 4
5
M = Ni, Pd
R = R' = t-Bu, Ph, 2,4,6-Me3C6H2 R = Ph, R'= 2,4,6-Me3C6H2 ArF = 3,5-(CF3) 2C6H3 Scheme 2 Cationic phosphino-phenol and keto-phosphine catalysts
Since fewer studies have appeared on the influence of electron-donating and steric
properties of the phosphorus substituents in neutral SHOP-type catalysts on the oligomer
distribution, 52 and encouraged by the positive effect on catalytic activity of donor substituents
in the phosphino-phenolate systems, 44-47 we decided to synthesize new β-keto phosphorus
ylids with alkyl substituents on the phosphorus atom and to evaluate their corresponding
nickel complexes in the catalytic oligomerization of ethylene.
2. Results and discussion
2.1 Synthesis of the β-keto phosphorus ylids
The ylids were prepared in two steps: synthesis of the phosphonium salt followed by its
deprotonation. 53 The reaction of tri(n-butyl)phosphine with α-bromoacetophenone in toluene
at room temperature afforded the phosphonium salt which, after dissolution in a mixture
MeOH/H2O (1/1) containing NaOH, afforded the corresponding β-keto phosphorus ylid 6,
which was characterized by 1 H, 13 C{ 1 H} and 31 P{ 1 H} NMR spectroscopy [eqn (2)].
Ph
O
Br + PR2R' 1) toluene
2) NaOH/MeOH/H 2O
or NaH/toluene
- HBr
Ph
O
PR 2R'
6 R = R' = n-Bu
7 R = t-Bu, R' = Ph
8 R = Ph, R' = t-Bu
9 R = n-Bu, R' = Ph
10 R = Ph, R' = n-Bu
11 R=Me,R'=Ph
However, reaction of 6 to [Ni(COD)2] in the presence of PPh3 did not yield the expected
complex and only decomposition to nickel metal was observed. There was no indication for
the migration of a n-butyl substituent from the phosphorus atom to the metal centre. 54
(2)
5