Copper PN(H)N Complexes: Synthesis of Pincer and Dinuclear Architectures and Base-Free C (sp3)-H Amidation Catalyzed by the Dinuclear Complex

Abstract

An amide-pyridine-monophosphine ligand, {(o-PPh₂)C₆H₄C(O)N(H)CH₂(C₅H₄N)} (1), was employed for the synthesis of Cu^I and Cu^II complexes. Reaction of ligand 1 with CuX (X = Cl, Br, I) in 1:1 molar ratio afforded bidentate dinuclear P,N-chelated Cu^I complexes of the type [(CuX)₂{(o-PPh₂)C₆H₄C(O)N(H)CH₂(C₅H₄N)}₂-κ²-P,N] (2–4; X = Cl, Br, I). In contrast, treatment of 1 with CuCl₂ under aerobic conditions in a CH₂Cl₂/CH₃CN (1:1) mixture yielded the tridentate mononuclear pincer complex {CuCl₂(o-OPPh₂)C₆H₄C(O)N(H)CH₂(C₅H₄N)-κ³-O,N,N} (5), while reaction with CuCl in a C₂H₄Cl₂/CH₃CN (1:1) solvent system gave the dinuclear analogue [(CuCl)₂{{(o-OPPh₂)C₆H₄}C(O)NCH₂(C₅H₄N)}₂-κ³-O,N,N] (6). Notably, the Cu^I dinuclear complex 4 catalyzed acid and base free direct amidation of unactivated alkanes and toluene derivatives via C (sp³)-N bond formation. This transformation proceeded efficiently through N-alkylation of phthalimide, sulfonamide, and benzamide, as well as activation of challenging C (sp³)-H bonds in cycloalkanes, alkenes, and benzylic substrates. The catalyst exhibited high activity at low loading, delivering excellent yields under mild conditions within short reaction times.