REVERSIBLE DEHYDROGENATION OF A HETEROBIMETALLIC POLYHYDRIDE COMPOUND

Li[RuH3(PPh3)3] reacts with [Ir(COD)Cl]2 to form a kinetic product, (COD)Ir(mu-H)3Ru(PPh3)3, which then isomerizes to (COD)Ir(mu-H)2RuH(PPh3)3 (1) as the thermodynamic product. The phosphines in this structure have the mer configuration. The ortho phenyl protons of the trans phosphine of 1 show temperature-dependent H-1 NMR behavior which may be related to subsequent reactivity observed at these positions. In solution at room temperature, 1 is in equilibrium with free H-2 and a dehydrogenated species. Upon removal of H-2, a new species (2) is formed. When 2 is placed under H-2, it reverts to 1, demonstrating the reversibility of this transformation. Spectroscopic data, as well as labeling studies, suggest that 2 contains a phosphine ortho metalated to ruthenium. The pi-cloud of the ortho-metalated phenyl ring may play a role in donation to iridium. Crystal data for 1 (at -172-degrees-C): a = 21.150 (8) angstrom, b = 22.186 (6) angstrom, c = 12.638 (3) angstrom, alpha = 91.55 (1)-degrees, beta = 90.85 (1)-degrees, gamma = 111.71 (1)-degrees with Z = 4 in space group P1BAR.