C(sp3)–H cyanation by a formal copper(iii) cyanide complex

Abstract

High-valent metal oxo complexes are prototypical intermediates for the activation and hydroxylation of alkyl C–H bonds. Substituting the oxo ligand with other functional groups offers the opportunity for additional C–H functionalization beyond C–O bond formation. However, few species aside from metal oxo complexes have been reported to both activate and functionalize alkyl C–H bonds. We herein report the first example of an isolated copper(III) cyanide complex (LCu^IIICN) and its C–H cyanation reactivity. We found that the redox potential (E_ox) of substrates, instead of C–H bond dissociation energy, is a key determinant of the rate of PCET, suggesting an oxidative asynchronous CPET or ETPT mechanism. Among substrates with the same BDEs, those with low redox potentials transfer H atoms up to a million-fold faster. Capitalizing on this mechanistic insight, we found that LCu^IIICN is highly selective for cyanation of amines, which is predisposed to oxidative asynchronous or stepwise transfer of H⁺/e⁻. Our study demonstrates that the asynchronous effect of PCET is an appealing tool for controlling the selectivity of C–H functionalization.