Synthesis, characterization, and structure of cyclopenta[c]thiophenes and their manganese complexes

1,3-Diaryl-4H-cyclopenta[c]thiophenes are efficiently prepared from 1,2-diaroylcyclopentadienes by use of Lawesson's reagent. η⁵-Cyclopenta[c]thienyl complexes, [Mn(η⁵-SC₇H₃-1,3-R₂)(CO)₃] (R = Me, Ph), are prepared in high yield by ligand substitution reactions of [MnBr(CO)₅] with [SnMe₃(SC₇H₃-1,3-R₂)]. Alternatively, thiation with P₄S₁₀/NaHCO₃ converts [Mn{η⁵-1,2-C₅H₃(COR)₂)(CO)₃] to [Mn(η⁵-SC₇H₃-1,3-R₂)(CO)₃] (R = Ph, 4-tolyl, 4-MeOC₆H₄, benzo[2,3-b]thienyl). The molecular structures of complexes with R = Me, Ph show planar η⁵-cyclopenta[c]thienyl ligands, with the manganese atom slightly displaced away from the ring-fusion bond.