The use of the tridentate ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me(3)tacn) and the cyclic alkyl/aryl C-donor ligand -CH2CMe2-o-C6H4- (cycloneophyl) allows for the synthesis of isolable organometallic Ni-II, Ni-III, and Ni-IV complexes. Surprisingly, the five-coordinate Ni-III, complex is stable both in solution and the solid state, and exhibits limited C-C bond formation reactivity. Oxidation by one electron of this Ni-III species generates a six-coordinate Ni-IV complex, with an acetonitrile molecule bound to Ni. Interestingly, illumination of the Ni-IV complex with blue LEDs results in rapid formation of the cyclic C-C product at room temperature. This reactivity has important implications for the recently developed dual Ni/photoredox catalytic systems proposed to involve high-valent organometallic Ni intermediates. Additional reactivity studies show the corresponding Ni-II species undergoes oxidative addition with alkyl halides, as well as rapid oxidation by O-2, to generate detectable Niln and/or Ni-IV intermediates and followed by C-C bond formation.