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] (<b>1</b>) prepared by a literature procedure [Young, R.; Wilkinson, G. Inorg. Synth. 1990, 28, 337] shows that <b>1</b> is cocrystallized with PPh₃, explaining the previously reported observations of free phosphine in solutions of <b>1</b>. Lattice PPh₃-free forms of <b>1</b> have also been obtained, structurally characterized, and found to generate small quantities of uncoordinated PPh₃ and another species (<b>A</b>) in solution. Against previous beliefs, however, <b>A</b> is not [(Ph₃P)₃­Ru­(H)₂] (<b>2</b>), but [(Ph₃P)₃­Ru­(H₂)­(H)₂] (<b>3</b>) that forms in the reaction of <b>1</b> with adventitious water. This reaction apparently occurs via PPh₃ loss from <b>1</b> to give <b>2</b>, followed by H₂O coordination, Ru­(H)­(OH₂)/​Ru­(H₂)­(OH) rearrangement, H₂ loss, and dimerization to give [(Ph₃P)₄­Ru₂(H)₂­(μ-OH)₂] (<b>4</b>). The H₂ thus produced is trapped with <b>2</b> to give <b>3</b>. Complexes <b>3</b>·0.5C₆H₆, <b>3</b>·2THF, <b>4</b>·2H₂O, [(Ph₃P)₃­Ru­(N₂)­(H)₂] (<b>5</b>), and [(Ph₃P)₂(H)­Ru­(μ-H)₃­Ru­(PPh₃)₃]·0.5THF (<b>6</b>·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]” (<b>7</b>) has been performed to finally demonstrate that <b>7</b> 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]