Synthesis, Neutron Structure, and Reactivity of the Bis(dihydrogen) Complex RuH<sub>2</sub>(η<sup>2</sup>-H<sub>2</sub>)<sub>2</sub>(PCyp<sub>3</sub>)<sub>2</sub> Stabilized by Two Tricyclopentylphosphines
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Treatment of Ru(η4-C8H12)(η6-C8H10) with 3 bar H2 in the presence of 2 equiv of tricyclopentylphosphine (PCyp3) in pentane resulted in the isolation of 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) Å) are characteristic of two “unstretched” dihydrogen ligands. H/D exchange between the Ru−H and the C−D bonds of deuterated benzene is observed within 1 h, leading to the formation of 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). We 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 temperature, prior to this work.
