Impact of Oxidation State on Reactivity and Selectivity Differences between Nickel(III) and Nickel(IV) Alkyl Complexes

Described is a systematic comparison of factors impacting the relative rates and selectivities of C(sp 3 )−C and C(sp 3 )−O bond‐forming reactions at high‐valent Ni as a function of oxidation state. Two Ni complexes are compared: a cationic octahedral Ni IV complex ligated by tris(pyrazolyl)borate and a cationic octahedral Ni III complex ligated by tris(pyrazolyl)methane. Key features of reactivity/selectivity are revealed: 1) C(sp 3 )−C(sp 2 ) bond‐forming reductive elimination occurs from both centers, but the Ni III complex reacts up to 300‐fold faster than the Ni IV , depending on the reaction conditions. The relative reactivity is proposed to derive from ligand dissociation kinetics, which vary as a function of oxidation state and the presence/absence of visible light. 2) Upon the addition of acetate (AcO − ), the Ni IV complex exclusively undergoes C(sp 3 )−OAc bond formation, while the Ni III analogue forms the C(sp 3 )−C(sp 2 ) coupled product selectively. This difference is rationalized based on the electrophilicity of the respective M−C(sp 3 ) bonds, and thus their relative reactivity towards outer‐sphere S N 2‐type bond‐forming reactions.