Access toHeterobimetallic M^II/Cu^I Complexes with a MultichelatePlatform and Their Reactivity Studiesin CO2RR

We describe the selective formation of heterobimetallic complexes, exploiting the coordination trends of the developed bis-terpyridyl <i>trans</i>-1,2-cyclohexadiamine platform (<b>L</b>). Following a stepwise addition, we first reacted ligand <b>L</b> toward tetrakisacetonitrile transition metal precursors, [M­(MeCN)₄]­[BF₄]₂ (where M = Fe or Ni), to generate the monometallic complexes <b>1</b> ([FeL]­[BF₄]₂) and <b>2</b> ([NiL]­[BF₄]₂). These species were later combined with the tetrakisacetonitrile precursor [Cu­(MeCN)₄]­[BF₄], generating the corresponding heterobimetallic complexes <b>3</b> ([FeCuL­(MeCN)₂]­[BF₄]₃) and <b>4</b> ([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 <b>1</b>–<b>4</b> 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 (<b>1</b> and <b>3</b>), generating CO with 88% selectivity.