Synthesis and mechanism study of a dimeric tetranuclear carbonate-bridged copper(II) complex resulting from CO2 fixation by controlling O2 concentration

A dimeric tetranuclear carbonate-bridged Cu(II) complex [Cu4(DPA-iBu)4(μ2-CO3)2(MeOH)2]4+ 1 was prepared in-situ through oxidation of Cu(I) species by controlling the concentration of O2 in CO2. Lower concentration of O2 led to the formation of 1 after CO2 fixation but higher would give product as bis-μ2-hydroxo complex [Cu(DPA-iBu)(OH)]22+ 2, which was found to be an intermediate to generate trinuclear carbonated complex [Cu3(DPA-iBu)3(μ3-CO3)(MeCN)2(H2O)]4+ 3. The mechanism of this reaction was proposed and the nucleophilic attack of μ-peroxo Cu(II) species to CO2 molecules was suggested to be responsible for the generation of 1.