C−S Bond Cleavage of Benzo[b]thiophene at Ruthenium

The ruthenium(II) (tetrahydroborate)hydride complex [(triphos)RuH(BH 4 )] ( 1 ) reacts with benzo[ b ]thiophene (BT) in THF at 40 °C yielding, after 3 h, a mixture of four different compounds: [(triphos)RuH{BH 3 ( o -S(C 6 H 4 )CH 2 CH 3 )}] ( 2 ), [(triphos)Ru{η 4 -S(C 6 H 4 )CH(CH 3 )}] ( 3 ), [(triphos)RuH(μ-S(C 6 H 4 )CH 2 CH 3 ) 2 HRu(triphos)] ( 4 ), and [(triphos)RuH(μ-BH 4 )HRu(triphos)] + ( 5 + ) (triphos = MeC(CH 2 PPh 2 ) 3 ). After two further hours of reaction, 3 disappears and is completely converted to 4 . Further heating at 40 °C does not change the product composition ( 2, 4, and 5 + in a 4:1.3:3 ratio). A variety of independent reactions with isolated compounds have been performed with the aim of elucidating the mechanism of the C−S insertion/hydrogenation of BT to the 2-ethylthiophenolate ligand. The μ-thiolate complex 4 reacts in THF with dihydrogen (≥160 °C, 30 bar H 2 ) or with HBF 4 ·OEt 2 (20 °C) yielding ethylbenzene and 2-ethylthiophenol, respectively. No reaction occurs with LiHBEt 3 . All of the reactions and new complexes reported have been studied by multinuclear NMR spectroscopy. An X-ray analysis has been carried out on a single crystal of 2 .