NICKEL PHENYL COMPLEXES WITH CHELATING KAPPA-2-P,O LIGANDS AS CATALYSTS FOR THE OLIGOMERIZATION OF ETHYLENE INTO LINEAR ALPHA-OLEFINS

Starting from [Ni(COD)(2)] and the phosphorus ylide Ph3P(o-C6H4O), the complexes [NiPh{Ph2P(o-C6H4O)}-(PR3)] [PR3 = PMe3 (2a), PMe2Ph (2b), PMePh2 (2c), PCy3 (2d), PPh3 (2e), PTol(3) (2f), P(p-C6H4OMe)(3) (2g), P(OMe)(3) (2h), P(p-C6H4Cl)(3) (2i), P(p-C6H4F)(3) (2j), P(p-C6H4CF3) (3) (2k)] were synthesized in the presence of the corresponding phosph ine. The bis-chelate complex cis-[Ni{Ph2P(o-C6H4O)}(2)] (3) was formed as a minor by-product during these reactions, but was the only isolab le compound when the reactions were conducted at temperatures above 60 degrees C. Oxidative addition of a P-Ph bond to the Ni-0 centre was a lso used to synthesize [NiPh{Ph2PCH - C(- O)Ph}(PMe3)] (1a) from the a lpha-ketophosphorus ylide Ph3P=CHC(=O)Ph and PMe3. Reaction of [Ph3P(o -C6H4NH2)]Br with [Ni(COD)(2)] and PTol(3) yielded the expected compou nd [NiPh{Ph2P(o-C6H4NH)}(PTol(3))] (6) via deprotonation of the NH2 fu nction by an excess of PTol(3). Experiments to study the potential of these nickel complexes as catalysts for ethylene oligomerization into linear alpha-olefins (> 95%) showed widely varying activities [500-180 000 mol C2H4 (mol catalyst h)(-1)] and mass distributions of the alpha -olefins. In contrast to the nickel phosphino enolate complexes of the type [NiPh{Ph2PCH - C(- O)Ph}(PR3)] [PR3 = PMe3 (1a), PCy3, (1b), PPh 3 (1c)], the corresponding nickel phosphino phenolates [NiPh{Ph2P(o-C6 H4O)}(PR3)] (2) generally showed a marked tendency to oligomerize ethy lene into alpha-olefins of higher molecular weight: C-4= to C-30= for 1 versus C-4= to C-90= for 2. The complex[NiPr{Ph6P(o-C6H4NH)}(PTol(3) )] (6), on the other hand, showed no activity for ethylene oligomeriza tion.