STRUCTURE AND REACTIVITY STUDIES OF THE UNUSUAL PEROXO-BRIDGED COMPLEX, [IR2I2(CO)2(MU-O2)(PH2PCH2PPH2)2] - THE 1ST COMPOUND HAVING A PEROXIDE MOIETY BRIDGING A METAL METAL BOND

Reaction of the diiodo complex [Ir2I2(CO)(mu-CO)(dppm)2] (1; dppm = Ph 2PCH2PPh2) with oxygen gives an unusual peroxo-bridged complex, [Ir2I2 (CO)2(mu-O2)(dppm)2] (2), in which the bridging dioxygen group is acco mpanied by a metal-metal bond. The reactivity of this species has been investigated. Thus, reaction of SO2 with 2 yields the sulfate-bridged compound [Ir2I2(CO)2(mu-SO4)(dppm)2] (3), which is also produced in t he reaction of 2 with CuSO4 and in the protonation of 2 with H2SO4, wi th release of H2O2. Reaction of 2 with NO2 and NO affords the nitrate- and nitrosyl-bridged compounds [Ir2I2(CO)2(mu-X)(dppm)2][NO3] (X = NO 3 (4a); NO (5)), respectively. The reaction with CO in CH2Cl2/CH3OH yi elds two compounds together with CO2. One of the species is identified as [Ir2(CO)2(mu-CO)(mu-I)(dppm)2][I], while the other one is shown to be a dioxygen compound, [Ir2I2(CO)2(mu-CO)(mu-O2)(dppm)2] (6), formed via formal CO insertion into the Ir-Ir bond of 2. In contrast, isocya nides (RNC; R = (i)Pr, (t)Bu) are not oxidized by 2; instead the hydro xide-bridged methoxycarbonyl species [Ir2(CO2CH3)(RNC)3(mu-CO)(mu-OH)( dppm)2][I]2 (R = (i)Pr (7); (t)Bu (8)) are obtained through involvemen t of the methanol solvent. Reaction of 2 with HCl yields two tetrahali de isomers [Ir2Cl2I2(CO)2(dppm)2] (9a,b). Attempted reactions with NO, HBF4.OEt2, and CH3SO3CF3 gave rise to the hydroxide-bridged complex [Ir2I2(CO)2(mu-OH)(dppm)2]+ (10), through involvement of adventitious water; although under dry conditions, reaction with NO+ yields 4, with the appropriate anion. The structures of 2 and 6 have been determined by X-ray crystallography. Complex 2 crystallizes in the tetragonal sp ace group P4(1)2(1)2 with a = 14.647(2) angstrom, c = 27.973(4) angstr om, V = 6001(1) angstrom3, and Z = 4 and has refined to R = 0.061 and R(w) = 0.093 on the basis of 3585 observations and 169 parameters vari ed. Complex 6 crystallizes in the orthorhombic space group Pna2(1) wit h a = 30.110(8) angstrom, b = 15.678(6), c = 12.020(6) angstrom, V = 5 674(7) angstrom3, and Z = 4 and has refined to R = 0.056 and R(w) = 0. 064 on the basis of 2598 observations and 328 parameters varied.