Isolation of OH-bridged Ag(i)/Cu(iii) and ion-pair Cu(i)/Cu(iii) trifluoromethyl complexes with monophosphines

Abstract

Cu(III)–CF₃ complexes are important intermediates of both synthetic and mechanistic interest. This study describes the isolation, and spectroscopic and X-ray crystallographic characterization of Cu^III–CF₃ complexes 2–4 with typical monophosphine ligands PPh₃ and Buchwald-type biarylmonophosphines. Distinct from the ion-pair [P₂Cu(I)]⁺[Cu(III)(CF₃)₄]⁻ structures of 2 and 4 (P: PPh₃ or SPhos), complex 3 exhibits a novel OH-bridged Ag(I)–Cu(III) dinuclear structure with XPhos-coordinated linear Ag(I) and square planar Cu(III) components. This is the first heterobimetallic Cu(III)–CF₃ complex confirmed by both solution-phase NMR spectroscopy and solid state X-ray crystal structure analysis. Complex 3 is found to have the LUMO orbital of major σ*(Cu–CF₃) nature and electrophilic CF₃ ligands. Accordingly, complex 3 is able to trifluoromethylate 2 equivalents of aryl boronic acids in up to quantitative yields, regardless of the inert or oxidative conditions. In contrast, the ion-pair complexes 2 and 4 show low reactivity. This study enriches the coordination and reactivity chemistry of Cu(III)–CF₃ compounds and shows the feasibility of modulation of structures and reactivity by ligand design, which may inspire future efforts on Cu(III)–CF₃ chemistry.