SULFUR-COORDINATED THIOPHENE AND BENZOTHIOPHENE IN CP(NO)(PPH(3))RE(THIOPHENE)(+) - CONVERSION TO THIENYL AND THIENYLCARBENE COMPLEXES

A series of stable sulfur-coordinated thiophene complexes Cp(NO)(PPh(3))Re(eta(1)(S)-Th)(+), Cp = eta(5)-C5H5, Th = thiophene (T), 2,5-Me(2)T, benzo[b]thiophene (BT), and 2-MeBT, are prepared by the reaction of Cp(NO)(PPh(3))Re(ClCH2Cl)(+) with thiophenes. The T and BT complexes react with bases to abstract a proton from the2-carbon of the eta(1)(S)-coordinated thiophenes to give neutral 2-thienyl (2-Tyl) or 2-benzothienyl (2-BTyl) complexes. [GRAPHICS] Reaction of the 2,5-Me(2)T complex with base results in proton abstraction at the 3-carbon to give the 3-(2,5-Me(2)Tyl) complex. The 2-Tyl and 2-BTyl complexes react with CF3SO3H to give cationic thienylcarbene and benzothienylcarbene complexes, respectively, which are isomers of the starting eta(1)(S)-coordinated thiophene complexes. This series of facile reactions demonstrates that eta(1)(S) coordination can activate thiophenes in a way that leads to the disruption of the aromaticity of the thiophene ligand upon formation of the thienylcarbene complexes. The base removal of the 2-proton from eta(1)(S)-thiophene ligands also suggests a mechanism for the exchange of these protons with deuterium during the hydrodesulfurization of thiophenes on heterogeneous catalysts.