INSERTION INTO THE NICKEL-CARBON BOND OF N-O CHELATED ARYLNICKEL(II) COMPLEXES - THE DEVELOPMENT OF SINGLE-COMPONENT CATALYSTS FOR THE OLIGOMERIZATION OF ETHYLENE

A series of arylnickel phosphine complexes containing chelating N-O li gands, of the type [NiAr(N-O)L] [N-O=pyridine carboxylate (pyca); Ar = o-tolyl; L = PPh(3), P(CH(2)Ph)(3), PMePh(2), PMe(2)Ph, PCy(3): R = p -tolyl; L = PPh(3): Ar = phenyl; L = PPh(3): R - mesityl; L = PMePh(2) : N-O = pyridine acetate (pyac); Ar = mesityl; L = PMePh(2)] have been prepared, providing complexes with chelate ring sizes of five and six . Crystal structures for the complexes indicate that both complexes ha ve ''square planar'' coordination about the nickel centre, with the ni trogen of the pyridine being trans to the phosphine in each case. Wher eas significant bending and buckling of the six-membered chelate ring is evident for [Ni(mesityl)(pyac)PMePh(2)], the five-membered ring of [Ni(mesityl)(pyca)PMePh(2)] is essentially planar. On warming the comp lexes readily insert ethylene into the Ni-aryl bond, forming single co mponent catalysts for the conversion of ethylene into higher oligomers with low to moderate activity. Products are linear with generally 60- 80% having the double bond in the alpha-position. Catalyst activities and product distributions are markedly dependent on the phosphine pres ent, Addition of excess PPh(3) to the catalyst [Ni(o-tolyl)(pyca)PPh(3 )] leads to a marked change in the product distribution with a less dr amatic change in catalyst activity. A possible mechanism in which ethy lene insertion occurs via an associative pathway from a five coordinat e intermediate, [NiAr(CH2=CH2)(pyca)PR(3)], is suggested.