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

• Published in: Chemical science (Cambridge) 2023-02, Vol.14 (5), p.131-137
• Main Authors: Bower, Jamey K, Reese, Maxwell S, Mazin, Ilia M, Zarnitsa, Lina M, Cypcar, Andrew D, Moore, Curtis E, Sokolov, Alexander Yu, Zhang, Shiyu
• Format: Article
• Language: English
• Subjects: Amines; Chemistry; Copper; Energy of dissociation; Free energy; Functional groups; Heat of formation; Hydrogen bonds; Hydroxylation; Selectivity; Substrates
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d2sc06573h

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 ( L Cu III CN) 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 L Cu III CN 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. A formal copper( iii ) cyanide complex and its C-H cyanation reactivity are reported. The redox potentials of substrates, instead of C-H bond dissociation energies, were found to be the key determinant of the rates of PCET.