Neutron Diffraction Studies of [Cp(PMe₃)₂RuH] and [Cp(PMe₃)₂RuH₂]BF₄ at 20 K

The crystal and molecular structures of [Cp(PMe 3 ) 2 RuH] ( 1 ) and [Cp(PMe 3 ) 2 RuH 2 ]BF 4 ( 2 ) have been determined from neutron diffraction measurements at 20 K. The Ru−H bond lengths in 1 (1.630(4) Å) and 2 (1.599(8), 1.604(9) Å) are the first terminal Ru−H distances to be determined by single-crystal neutron diffraction. The “Cp‘L 2 Ru” system is now the first to have neutron diffraction studies of the monohydride, dihydride, and dihydrogen species. This is of particular importance in understanding the activation of H 2 by this metal−ligand fragment. Thus detailed comparisons with the recent structure determination by neutron diffraction of the dihydrogen complex [Cp*(dppm)Ru(η 2 -H 2 )]BF 4 (dppm = bis(diphenylphosphino)methane) [Klooster, W. T.; Koetzle, T. F.; Jia, G.; Fong, T. P.; Morris, R. H.; Albinati, A. J . Am . Chem . Soc . 1994, 116, 7677−7681] are presented. A network of C−H···F−BF 3 hydrogen bonds links the anion and cation moieties in 2 . The C(2)−H(2)···F(4) interaction has an H···F separation of only 2.078(8) Å, the shortest such interaction characterized to date by neutron diffraction. Ru−H stretching frequencies determined from the diffraction data are in good agreement with those from IR measurements.