Cyclometalated Organonickel Complexes through C-H and C-X Activation

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New cyclometalated organonickel(II) complexes with anionic tridentate CNN or NCN ligands will be synthesised from Ni(0) or Ni(II) precursors through C-X or C-H bond activation and metalation of the C donor function of the tridentate ligands. Several potential mechanistic variations will be explored: (a) Oxidative addition of proto-ligand C-X functions to Ni(0) precursor complexes, (b) C-H deprotonation and binding to Ni(II), (c) oxidative addition of C-H to Ni(0) or Ni(II), and (d) electrochemically induced C-Ni coupling starting from C-H or C-X functionalised proto-ligands and Ni(II); presumably involving radical steps. While C-X oxidative addition to Ni(0) is an established procedure and the C-H activation through deprotonation has been previously reported, the C-H activation by Ni(0) represents a big challenge and electrochemically induced procedures are unprecedented. The new cyclometalated complexes and also the proto-ligands and complex precursors will be analytically, spectroscopically and electrochemically characterised to explore the steric and electronical prerequisites for a successful cyclometalation reaction and the differences between cyclometalated complexes and non-cyclometalated derivatives. Quantum chemical calculations will add to the understanding. This study on C-H and C-X activation will allow detailed insight into one of the key steps of C-C coupling catalysis and into the structure and electronics of such cyclometalated organonickel complexes as key intermediates.