Tridentate pincer-type ligands offer both electronic and steric flexibility, and have been used to stabilize highly reactive species such as metal nitrides, metal hydrides, etc. Nickel complexes supported by tridentate pincer ligands have been shown to be remarkable catalysts in a variety of important organic transformations including C-C coupling, CO2 reduction, and reductive functionalization of unsaturated organic substrates. Herein, we report a series of novel nickel complexes bound by a pincer-type bis(phosphinimine) ligand framework {HN(1,2-C6H4N=PPh2Me)2}. The redox non-innocence of the phosphinimine ligand was explored, and oxidation of a nickel phenoxide complex was shown to be primarily ligand-centered. Photoreduction of a nickel azide complex bound by this ligand resulted in the activation of a ligand CH3 group, hereby generating a four-membered metallacycle. The Ni-C bond in this complex exhibits versatile reactivity toward CO and isocyanide insertion reactions as well as H-E (E= C, O, S) bond activation. Of particular interest is the ability of this complex to formally abstract a sulfur atom from triphenylmethyl thiol, concomitant with the formation of triphenylmethane, suggesting the intermediacy of a nickel sulfide.

Formation of a Ni-C four-membered metallacycle and its reactivity toward X-Y bond activation

2019 Fall National Meeting

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