Oxidative C–C Bond Formation Reactivity of Organometallic Ni(II), Ni(III), and Ni(IV) Complexes

The use of the tridentate ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me 3 acn) and the cyclic alkyl/aryl C-donor ligand -CH 2 CMe 2 -o-C 6 H 4 - (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 Ni III and/or Ni IV intermediates and followed by C-C bond formation.