Mimicking the HDS Activity of Ruthenium-Based Catalysts 2: The Hydrogenation of Benzo[b]thiophene to 2,3-Dihydrobenzo[b]thiophene

Abstract

The ruthenium(II) tris-acetonitrile complex [(triphos)Ru(MeCN)3]BPh4 (1) is an extremely efficient catalyst precursor for the regioselective hydrogenation of benzo[b]thiophene (BT) to 2,3-dihydrobenzo[b]thiophene (DHBT) in homogeneous phase under mild reaction conditions (THF, 40−100 °C, 1−30 bar H2) [triphos = MeC(CH2PPh2)3]. At 30 bar of H2 and 100 °C, BT is converted to DHBT with an average rate of 500 mol of product (mol of cat)-1 h-1. During the catalytic reactions with PH2 > 5 bar, the acetonitrile ligands in 1 are transformed into a mixture of NHEt2, NEt3, and NH3, while the termination ruthenium products are the monohydrido complexes [(triphos)Ru(H)(NH3)2]BPh4, [(triphos)Ru(H)(NH3)(NH2Et)]BPh4, and [(triphos)Ru(H)(NH3)(η1-S-DHBT)]BPh4. Below 5 bar of H2, no hydrogenation of MeCN occurs and all of the ruthenium is recovered as [(triphos)Ru(H)(NCMe)(η1-S-DHBT)]BPh4. All of these Ru(II) hydrido complexes catalyze the hydrogenation of BT to DHBT as efficiently as 1. The substitution of D2 for H2 in a ...