Electron-Transfer Activation of Coordinated Thiophene: Preparation and Desulfurization of (η⁵-C₅Me₅)Rh(η⁴-C₄Me₄S)

Cyclic voltammetry studies show that [(C₅Me₅)Rh(C₄Me₄S)]²⁺ undergoes two reversible one-electron reductions at low potentials. The reduced product was synthesized by cobaltocene reduction and was characterized as [(η⁵-C₅Me₅)Rh(η⁴-C ₄Me₄S)]. ¹H and ¹³C NMR spectroscopic results are consistent with a symmetrical, reduced thiophene ligand. An X-ray crystallographic study confirms that the reduced complex contains a nonplanar η⁴-thiophene ligand with an uncoordinated sulfur atom. The reduced complex reacts with Fe₃(CO)₁₂ to give (C₅Me₅)RhC₄Me₄Fe(CO)₃ which is analogous to a major product in the Fe₃(CO)₁₂ desulfurization of thiophenes. Electron-transfer activation is proposed to be relevant to the desulfurization of thiophenes by metal surfaces.