Solid-State Structure and Solution Reactivity of [(Ph3P)4Ru(H)2] and Related Ru(II) Complexes Used in Catalysis: A Reinvestigation

X-ray analysis of [(Ph3P)4Ru­(H)2] (1) prepared by a literature procedure [Young, R.; Wilkinson, G. Inorg. Synth. 1990, 28, 337] shows that 1 is cocrystallized with PPh3, explaining the previously reported observations of free phosphine in solutions of 1. Lattice PPh3-free forms of 1 have also been obtained, structurally characterized, and found to generate small quantities of uncoordinated PPh3 and another species (A) in solution. Against previous beliefs, however, A is not [(Ph3P)3­Ru­(H)2] (2), but [(Ph3P)3­Ru­(H2)­(H)2] (3) that forms in the reaction of 1 with adventitious water. This reaction apparently occurs via PPh3 loss from 1 to give 2, followed by H2O coordination, Ru­(H)­(OH2)/​Ru­(H2)­(OH) rearrangement, H2 loss, and dimerization to give [(Ph3P)4­Ru2(H)2­(μ-OH)2] (4). The H2 thus produced is trapped with 2 to give 3. Complexes 3·0.5C6H6, 3·2THF, 4·2H2O, [(Ph3P)3­Ru­(N2)­(H)2] (5), and [(Ph3P)2(H)­Ru­(μ-H)3­Ru­(PPh3)3]·0.5THF (6·0.5THF) have been structurally characterized for the first time. Also for the first time, a single-crystal X-ray diffraction study of the long-known “[(Ph3P)4RuCl2]” (7) has been performed to finally demonstrate that 7 is, in fact, [(Ph3P)3RuCl2]·PPh3, precisely as proposed by Hoffman and Caulton as early as 1975 [Hoffman, P.R.; Caulton, K.G. J. Am. Chem. Soc. 1975, 97, 4221].