(Tetramethylthiophene)ruthenium Dichloride Dimer: A Versatile Synthetic Intermediate in Thiophene Coordination Chemistry

The thermal reaction of [(cymene)RuCl₂]₂ and tetramethylthiophene (TMT) gives [(TMT)RuCl₂]₂ (1). Treatment of 1 with silver salts in the presence of various ligands gives salts of [(TMT)RuL₃]²⁺ where L₃ = (H₂O)₃, (CH₃CN)₃, and TMT. A crystallographic study demonstrated that [(TMT)₂Ru](BF₄)₂·2CH₃NO ₂ adopts a sandwich structure with sulfur atoms sited cis on the pseudooctahedron. Cyclic voltammetry studies show that [(TMT)₂Ru]²⁺ undergoes two reversible one-electron reductions. Solutions of 1 and phosphine and amine donors react to give well-behaved monometallic derivatives of the type (TMT)RuCl₂L where L is PR₃ and NH₂C₆H₄Me. For bulky L = PPh₃ and P(C₆H₄Me)₃, variable-temperature NMR studies demonstrate hindered rotation about the Ru-P and Ru⋯TMT axes. Treatment of 1 with (Me₃Si)₂S gives the cluster [(TMT)RuCl]₃S⁺ whose PF₆^- salt was examined by X-ray crystallography. The cluster is comprised of three conjoined pseudooctahedral Ru centers bridged by one μ₃-S and three μ-Cl atoms.