Intramolecular O–H ⋯ O–Ni and N–H ⋯ O–Ni hydrogen bonding in nickel diphenylphosphinoenolate phenyl complexes: role in catalytic ethene oligomerisation; crystal structure of [NiPH{Ph 2 PCHC(O)(o-C 6 H 4 NHPh)}(PPh 3 )]

Nickel diphenylphosphinoenolate complexes are prepared from ortho-HX-substituted phenacylidenetriphenylphosphoranes (X = O, NMe, NPh) which display strong intramolecular hydrogen bonding between the enolate oxygen and the H–X function; this feature dramatically influences the molecular mass distribution of the oligomers obtained by catalytic oligomerisation of ethene.