Oxidation addition of H-H bonds to iridium: developing novel active water soluble catalysts for hydrogenation of unsaturates

The oxidative addition of H-H to iridium(l) trimethylphosphine complexes was studied and the reactivity of the resulting water soluble dihydrido iridium (III) complexes was investigated. One Dihydrido iridium(III) complex, mer-Ir(H)₂(PMe₃)₃CI (2) was characterized by ¹H, ³¹p and ¹³C NMR spectroscopy, CH analysis and single crystal xray diffraction. (2) reacted with the strong sigma donor PMe₃ to form [IrH2(PMe₃)4]CI (3b) without having to remove the chloride ligand. (2) reacted with monosubstituted acetylenes and an internal diyne in water to form the vinyl complexes Ir(H)(C(R')=C(H)-(R))(PMe₃)₃CI (R = CMe₃, C₆H₅, SiMe₃, R' = H, (4)-(6); R' = CCMe₃, R= Me, (7)). (2) also reacted in water with ethynylpyridine to form an unusual metallacycle "trimer" (8). A mechanism for tltrimerizationtl is proposed. (2) also reacted with ethylene in water to form the diethyl iridium complex Ir(CH₂CH₃)₂(PMe₃)₃CI (8). Encouraged by these results, catalytic hydrogenation of unsaturates in water was investigated. It was found that (2) is active as a water soluble catalyst for hydrogenation of unsaturates. A mechanism for catalytic hydrogenation was proposed.