Synthesis, Neutron Structure, and Reactivity of the Bis(dihydrogen) Complex RuH2(η2-H2)2(PCyp3)2 Stabilized by Two Tricyclopentylphosphines

Treatment of Ru(η4-C8H12)(h6-C8H10) with 3 bar H2 in the presence of 2 equiv of tricyclopentylphosphine (PCyp3) in pentane gave the new bis(dihydrogen) complex RuH2(η2-H2)2(PCyp3)2 (2), characterized by NMR and single-crystal x-ray and neutron diffraction. The single-crystal neutron diffraction study is the first carried out for a bis(dihydrogen) complex. The coordination geometry around the metal center is a distorted octahedron defined by the two phosphines in a trans configuration (making an angle of 168.9(1)°), two cis dihydrogen ligands, and two hydrides trans to them, defining the equatorial plane. The H-H bond distances (0.825(8) and 0.835(8) .ANG.) are characteristic of two unstretched dihydrogen ligands. H/D exchange between the Ru-H and the C-D bonds of deuterated benzene is obsd. within 1 h, giving various isotopomers RuHxD6-x(PCyp3)2 (with x = 0-6). 2 Is a catalyst precursor for ethylene coupling (20 bar, 293 K) to a functionalized arene (Murai reaction). The authors found a 90% conversion of acetophenone to 2-ethylacetophenone within 35 min, whereas 10 h was needed in the same conditions using the analogous tricyclohexylphosphine complex, RuH2(η2-H2)2(PCy3)2, the best catalyst precursor, at room temp., prior to this work.