Reactivity of the Bis(dihydrogen) Complex [RuH2(η2-H2)2(PCy3)2] toward S-Heteroaromatic Compounds. Catalytic Hydrogenation of Thiophene

Room-temperature stoichiometric reaction of the bis(dihydrogen) complex [RuH 2 ( η 2 -H 2 ) 2 (PCy 3 ) 2 ] ( 1 ) with thiophene leads to the formation of a new complex that has been isolated and characterized as an η 4 -thioallyl complex [RuH( η 4 ( S,C )-SC 4 H 5 )(PCy 3 ) 2 ] ( 2 ). This complex easily regenerates 1 upon treatment with dihydrogen and can be successfully used as a catalyst precursor in thiophene hydrogenation to 2,3,4,5-tetrahydrothiophene (THT). The reaction of 1 with 2-acetylthiophene leads to a regioselective 1,5-C−S bond splitting with formal hydrogenation of two double C C bonds and coordination of a new 2-hexen-2-olato-3-thiolato ligand in an η 2 ( O, S ) mode to form [RuH 2 { η 2 ( O,S )-C 6 H 10 OS}(PCy 3 ) 2 ] ( 3 ). The new complex 3 has been characterized by 1 H, 31 P, and 13 C NMR studies including 1 H DPFGSE TOCSY, 2D- 1 H− 1 H{ 31 P} COSY DQF, and the correlated 13 C− 1 H HMQC LR spectra. The solid state molecular structure of 3 has been unequivocally determined by single-crystal X-ray structure analysis. The bis(dihydrogen) complex 1 is an effective catalyst precursor for the homogeneous hydrogenation of thiophene (T) to 2,3,4,5-tetrahydrothiophene (THT), 2-methylthiophene (2-MeT) to 2-methyltetrahydrothiophene (2-MeTHT), 2-acetylthiophene (2-AcT) to 1-(2-thienyl)ethanol (1-(2-Tyl)E), 2-thiophenecarboxaldehyde (2-TA) to 2-thiophenemethanol (2-TM), and benzo[ b ]thiophene (BT) to 2,3-dihydrobenzo[ b ]thiophene (DHBT) under mild conditions (80 °C, 3 bar H 2 ). Dibenzo[ b,d ]thiophene (DBT) is not reduced under these conditions due to the formation of the S-coordinated dihydrogen complex [RuH 2 ( η 2 -H 2 ){ η 1 ( S )-C 12 H 8 S}(PCy 3 ) 2 ] ( 4 ).