MIXED IRIDIUM-GOLD HYDRIDES AS MODEL COMPOUNDS FOR ELUCIDATING THE INTERCONVERSION BETWEEN CLASSICAL AND NONCLASSICAL POLYHYDRIDES

The reaction of [(triphos)Ir(H)(C2H4)] (1) or [(triphos)Ir(H)2(C2H5)] (2) with [Au(THF)(PPh3)]PF6 under ethylene produces the monogold adduct [(triphos)Ir(H)(C2H4){Au(PPh3)}]PF6 (3) which exhibits a terminal hydride ligand in the solid state, but contains a bridging hydride in solution [triphos = CH3C(CH2PPh2)3]. Addition of 1 equiv of [AuCl(PPh3)] to 3 yields the iridium-digold adduct [(triphos)(Cl)Ir(mu-H){Au2(PPh3)2}]PF6 (4). Complex 4 and its arsino analogue [(triphos)(Cl)Ir(mu-H){Au2(AsPh3)2}]PF6 (5) can be prepared straightforwardly by reacting 1 or 2 with 2 equiv of [AuCl(EPh3)] (E = P, As) in the presence of NH4PF6. The structure of 4 has been determined by X-ray diffraction. Crystals are triclinic, space group P1BAR with a = 14.317 (6) angstrom, b = 17.626 (4) angstrom, c = 17.791 (2) angstrom, alpha = 90.82 (1)-degrees, beta = 110.41 (2)-degrees, gamma = 112.31 (2)-degrees, V = 3836 (4) angstrom3, and Z = 2. The iridium center is coordinated in a distorted octahedral environment by the triphos ligand, a chlorine atom, and two Au(PPh3) units with the two gold atoms linked to each other. A crystallographically located hydride ligand bridges one of the two Ir-Au edges in the triangular IrAu2 moiety. All of the mixed iridium-gold complexes are fluxional in solution. The fluxional processes have been studied by variable-temperature P-31{H-1} NMR and H-1 NMR spectroscopy.