Access to Heterobimetallic M^II/Cu^I Complexes with a Multichelate Platform and Their Reactivity Studies in CO2RR

We describe the selective formation of heterobimetallic complexes, exploiting the coordination trends of the developed bis-terpyridyl trans-1,2-cyclohexadiamine platform (L). Following a stepwise addition, we first reacted ligand L toward tetrakisacetonitrile transition metal precursors, [M(MeCN)₄][BF₄]₂ (where M = Fe or Ni), to generate the monometallic complexes 1 ([FeL][BF₄]₂) and 2 ([NiL][BF₄]₂). These species were later combined with the tetrakisacetonitrile precursor [Cu(MeCN)₄][BF₄], generating the corresponding heterobimetallic complexes 3 ([FeCuL(MeCN)₂][BF₄]₃) and 4 ([NiCuL(MeCN)₂][BF₄]₃). The four species obtained, in high yields, have been structurally characterized. Their cyclic voltammetry analysis revealed the impact of the Cu^I-atom presence on the heterobimetallic complexes under argon and carbon dioxide (CO₂) atmospheres. Controlled potential electrolysis studies revealed the instability of complexes 1-4 toward CO2RR, generating the heterogeneous material in solution and on the electrode surface. In contrast, CO₂ photoreduction studies revealed higher stability and photocatalytic activity for the Fe^II-based complexes (1 and 3), generating CO with 88% selectivity.