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

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 ((LCuCN)-C-III) 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 (LCuCN)-C-III 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.

Automated summary

High-valent metal oxo complexes are important intermediates for the activation and hydroxylation of alkyl C-H bonds. In this study, an isolated copper(iii) cyanide complex and its C-H cyanation reactivity were reported. The redox potential of the substrates was found to be a key factor in determining the rate of proton-coupled electron transfer (PCET) reactions, suggesting an oxidative asynchronous mechanism. Based on this mechanistic insight, the copper(iii) cyanide complex demonstrated high selectivity for the cyanation of amines.