Well-Defined Cobalt(I) Dihydrogen Catalyst: Experimental Evidence for a Co(I)/Co(III) Redox Process in Olefin Hydrogenation

The
synthesis of a cobalt dihydrogen CoI-(H2) complex
prepared from a CoI-(N2) precursor
supported by a monoanionic pincer bis­(carbene) ligand, MesCCC (MesCCC = bis­(mesityl-benzimidazol-2-ylidene)­phenyl),
is described. This species is capable of H2/D2 scrambling and hydrogenating alkenes at room temperature. Stoichiometric
addition of HCl to the CoI-(N2) cleanly affords
the CoIII hydridochloride complex, which, upon the addition
of Cp2ZrHCl, evolves hydrogen gas and regenerates the CoI-(N2) complex. Furthermore, the catalytic olefin
hydrogenation activity of the CoI species was studied by
using multinuclear and parahydrogen (p-H2) induced polarization (PHIP) transfer NMR studies to elucidate catalytically
relevant intermediates, as well as to establish the role of the CoI-(H2) in the CoI/CoIII redox
cycle.