OLIGOPHOSPHINE LIGANDS .37. STEREOCHEMICAL FEATURES OF COMPLEXES CONTAINING THE CIS-L4RU FRAGMENT - MOLECULAR-STRUCTURES OF (ME3P)4RUH2 AND (P[(CH2)3PME2]3)RUH2

The title compounds have been studied by single-crystal X-ray diffraction. Both structures can be described as distorted octahedra. P-Ru-P angles between phosphorus atoms at mutually cis positions are considerably larger than 90-degrees, with the sum of the cis angles amounting to 495.6 for (Me3P)4RuH2 (1) and to 486.2 for P[(CH2)3PMe2]3}RuH2 (2). These structural parameters and the observed bending over of the two axial donor sets toward the hydrido ligands, which results in trans P-Ru-P angles of 151.5 for complex 1 and of 153-degrees for structure 2 averaged over four crystallographically independent molecules, suggest a considerably higher degree of steric encumbrance in cis-(Me3P)4Ru than in {P[(CH2)3PMe2]3}Ru systems. They thus correspond to both the well-known ability of the {P[(CH2)3PMe2]3}Ru(0) fragment to insert across C-H bonds of non-coordinated hydrocarbons and the propensity of cis-(Me3P)4Ru(0) to undergo spontaneous cyclometallation. Selected bond lengths of compound 1 are: Ru-P (trans ligand H), 2.306(1) and 2.306(2) angstrom; Ru-P (trans to each other), 2.276(1) and 2.289(2) angstrom. For the averaged structure 2, the mean distances between the central metal and the donor atoms are 2.270(5) angstrom for the bridging phosphorus atom, 2.292(6) angstrom for the PMe2 group trans to hydrogen, and 2.281(7) and 2.284(10) angstrom for the PMe2 substituents situated at mutually trans positions.