Influence of intramolecular N-H...O-Ni hydrogen bonding in nickel(II) diphenylphosphinoenolate phenyl complexes on the catalytic oligomerization of ethylene

Nickel(II) diphenylphosphinoenolate complexes have been prepared from (ortho-HX-substituted benzoylmethylene)triphenyl phosphoranes (X = NMe, NPh) and [Ni(1,5-cod)(2)] in the presence of a tertiary phosphine (PPh3 or P(p-C6H4F)(3)). An X-ray diffraction study of the complexes [NiPh{Ph2CH...C(...O)(o-C6H4NHMe)}(PPh3)] 10 and [NiPh{Ph2PCH...C(...O)(o-C6H4NHPh)}P(p-C6H4F)(3)}] 16 establishes the presence of strong intramolecular hydrogen bonding between the enolate oxygen and the N-H function, as originally found in [NiPh{Ph2PCH...C(...O)(o-C6H4NHPh)}(PPh3)] 11. This feature favours the formation of the desired shorter-chain-length products in the catalytic oligomerisation of ethylene.