Paddlewheel-type dirhodium complexes with N,N’-bridging ligands

Abstract

Paddlewheel-type dirhodium (Rh2) complexes with N,N’-bridging ligands such as formamidate ions, which have a single bond within the dinuclear core, are redox-active and adopt four oxidation states (Rh23+, Rh24+, Rh25+, and Rh26+) depending on the kinds of coordination ligands at the equatorial and axial positions of the Rh2 bond. N,N’-bridging ligands possess a strong σ-donating ability, which significantly induces the destabilization of π*(Rh2) and δ*(Rh2) orbitals, and strongly coordinate to the metal center compared with other O,O’- and N,O-bridging ligands. Therefore, Rh2 complexes with N,N’-bridging ligands show unique near-infrared absorption and electrochemical properties. This review summarizes the synthesis, crystal structures, electrochemical behaviors, absorption features, and magnetic properties of paddlewheel-type Rh2 complexes with N,N’-bridging ligands, [Rh2(L)4] (L = N,N’-diarylformamidinate, 2-anilinopyridinate, etc.).