Influence of a diimine ligand and an activator on the processes taking place in Brookhart-type nickel catalytic systems

Brookhart-type catalytic systems based on zero-valent nickel complexes Ni(COD) 2 and Ni(COD)L [where COD is cyclooctadiene and L is bis-2,6-diisopropylphenyl-diazabutadiene (DPP-DAB) or N , N ′-bis-2,6- diisopropylphenyl-bis-iminoacenaphthene (DPP-BIAN)] activated with Lewis acids such as methylaluminoxane (MAO) and boron trifluoride etherate BF 3 ·OEt 2 were investigated via electron spin resonance (ESR) spectrometry, revealing that presence of diimine ligand results in Lewis acids, formally oxidating Ni(0) to Ni(I). An oxidation mechanism is proposed.