2‐Dialkyl‐ and 2‐tert‐Butylphenylphosphinophenol(ate) Nickel and Palladium Complexes: Control of E/Z‐Configuration in Bis(P∩O—‐chelates) and Activation of the Nickel Complexes for Polymerization of Ethylene

Nickel bis(2‐dialkylphosphinophenolates), detected as the spent form of organonickel 2‐dialkylphosphinophenolate catalysts for the polymerization of ethylene, were studied. In contrast to the impact of the P‐basicity on the catalyst properties, the configuration of bis(2‐dialkylphosphinophenolate) nickel is controlled only by steric effects. Small alkyl substituents favor, as do phenyl groups, square planar cis‐bis(P∩O—‐chelates) while more bulky alkyl groups lead to trans‐isomers. Dicyclohexyl‐ and tert‐butylphenylphosphino groups give rise to borderline cases. Analogous palladium complexes show a slightly smaller effect of the metal size on the cis/trans‐control. Intermediates on the way to PdII bis(P∩O—‐chelates), trans‐dichloro‐bis(phosphinophenol)‐ and chloro‐phosphinophenol phosphinophenolate palladium(II) complexes could be isolated; the crystal structure of one of the latter was determined. The nickel bis(2‐dialkylphosphinophenolates) can be activated as polymerization catalysts, to a limited extent by NiBr2·DME and sodium hydride or triethylsilane in THF, more efficiently by nBuLi or nBuLi / NiBr2·DME.