Labile Cu(I) Catalyst/Spectator Cu(II) Species in Copper-Catalyzed C–C Coupling Reaction: Operando IR, in Situ XANES/EXAFS Evidence and Kinetic Investigations

Insights toward the Cu-catalyzed C–C coupling reaction were investigated through operando IR and in situ X-ray absorption near-edge structure/extended X-ray absorption fine structure. It was found that the Cu­(I) complex formed from the reaction of CuI with β-diketone nucleophile was liable under the cross-coupling conditions, which is usually considered as active catalytic species. This labile Cu­(I) complex could rapidly disproportionate to the spectator Cu­(II) and Cu(0) species under the reaction conditions, which was an off-cycle process. In this copper-catalyzed C–C coupling reaction, β-diketone might act both as the substrate and the ligand

Direct Observation of Reduction of Cu(II) to Cu(I) by Terminal Alkynes

X-ray absorption spectroscopy and <i>in situ</i> electron paramagnetic resonance evidence were provided for the reduction of Cu­(II) to Cu­(I) species by alkynes in the presence of tetramethylethylenediamine (TMEDA), in which TMEDA plays dual roles as both ligand and base. The structures of the starting Cu­(II) species and the obtained Cu­(I) species were determined as (TMEDA)­CuCl₂ and [(TMEDA)­CuCl]₂ dimer, respectively