Valence-Inverted States of Nickel(II) Complexes Perform Facile C-H Bond Activation

Valence-inverted reactivity (VIR) is discovered here through high-level computations of excited states of Ni(II) complexes that are generated by triplet energy transfer. For example, the so-generated ³[(Ar)(bpy)Ni^II(Br)] species possesses a valence-inverted occupancy, d¹d¹d_x², wherein the uppermost d_x orbital is metal-ligand antibonding. This state promotes C-H bond activation of THF and its cross-coupling to the aryl ligand. Thus, due to the metal-ligand antibonding character of d_x, the d¹d_x² subshell opens a Ni-coordination site by shifting the bidentate bipyridine ligand to monodentate plus a dangling pyridine. The tricoordinate Ni(II) intermediate inserts into a C-H bond of THF, transfers a proton to the dangling pyridine moiety, and eventually generates an arylated THF by reductive-coupling. The calculated high kinetic isotope effect is in accord with experiment, both revealing C-H activation. The VIR pattern is novel, its cross-coupling reaction is highly useful, and it is generally expected to occur in other d⁸ complexes.