Enhancing the Air Stability of Dimolybdenum Paddlewheel Complexes: Redox Tuning through Fluorine Substituents

The optical and electrochemical properties of quadruply bonded dimolybdenum paddlewheel complexes (Mo₂PWCs) make them ideal candidates for incorporation into functional materials or devices, but one of the greatest bottlenecks for this is their poor stability toward atmospheric oxygen. By tuning the potential at which the Mo₂ core is oxidized, it was possible to increase the tolerance of Mo₂PWCs to air. A series of homoleptic Mo₂PWCs bearing fluorinated formamidinate ligands have been synthesized and their electrochemical properties studied. The oxidation potential of the complexes was tuned in a predictable fashion by controlling the positions of the fluorine substituents on the ligands, as guided by a Hammett relationship. Studies into the air stability of the resulting complexes by multinuclear NMR spectroscopy show an increased tolerance to atmospheric oxygen with increasingly electron-withdrawing ligands. The heteroleptic complex Mo₂(D^FArF)₃(OAc) [where D^FArF = 3,5-(difluorophenyl)formamidinate] shows remarkable tolerance to oxygen in the solid state and in chloroform solutions. Through the employment of easily accessible ligands, the stability of the Mo₂ core toward oxygen has been enhanced, thereby making Mo₂PWCs with electron-withdrawing ligands more attractive candidates for the development of functional materials.