Mechanism of Heterolysis of H2 by an Unsaturated d8 Nickel Center: via Tetravalent Nickel?

摘要

It is reasonable to generalize that the initial interaction of H2nwith any metal center is to form an η2n-H2 complex.n1 4nHowever,nthe vast majority of isolated examples of this type5nhave the d6nelectronic configuration, while we will deal here with a d8nspecies.nWhen the o erall observed reaction is the heterolytic splitting ofnH2, to form H and H , cationic η2n-H2 complexes are the mostnBrønsted acidic, thus showing the greatest tendency for suchnsplitting of H2. Generally this heterolysis requires a Brønsted basento receive the H , and a series of papers on H2 heterolysis by NinIInshowed6 8nthat this is greatly facilitated when the base is ancomponent of some ligand, so that the proton transfer is intramo-nlecular; this is also the core of known polar multiple bondnhydrogenation catalysis where one ligand is an amide.