Spectral Studies of a Cr(PNP)–MAO System for Selective Ethylene Trimerization Catalysis: Searching for the Active Species

Variable temperature spectroscopic, kinetic, and chemical studies were performed on a soluble CrIIICl3(PNP) (PNP = bis(diarylphosphino)alkylamine) ethylene trimerization precatalyst to map out its methylaluminoxane (MAO) activation sequence. These studies indicate that treatment of CrIIICl3(PNP) with MAO leads first to replacement of chlorides with alkyl groups, followed by alkyl abstraction, and then reduction to lower–valent species. Reactivity studies demonstrate that the majority of the chromium species detected are not catalytically active.