Mimicking the HDS Activity of Ruthenium-Based Catalysts. Homogeneous Hydrogenolysis of Benzo[b]thiophene

Abstract

The reaction of [(triphos)RuH(BH4)] (1) in THF with KOBut yields the novel trihydride complex K[(triphos)RuH3] (2) and BH2OBut (triphos = MeC(CH2PPh2)3). The ruthenate complex 2 can also be synthesized by hydrogenation (30 bar of H2) in THF of the tris(acetonitrile) complex [(triphos)Ru(NCMe)3](BPh4)2 (3) in the presence of a 5-fold excess of BH2OBut at 40 °C. This reaction produces a mixture of NH2Et, NHEt2, NEt3, and NH3 as a result of MeCN hydrogenation, followed by amine redistribution reactions. Compound 2 is isolated in analytically pure form as [K(C12H24O6)][(triphos)RuH3] (2a) by recrystallization from THF/n-hexane in the presence of 18-crown-6 ether. In the presence of a strong base such as KOBut, both 1 and 3 are effective catalyst precursors for the homogeneous hydrogenolysis of benzo[b]thiophene (BT) to 2-ethylthiophenol (ETP) in THF under mild reaction conditions (≥70 °C, 30 bar of H2). The hydrogenolysis rate increases with the concentration of the base, which, depending on the catalyst prec...