Hydridoiridium(III) sulfoxide complexes and their reactivity toward dioxygen

Synthetic routes to hydridoiridium(III) dimethylsulfoxide complexes via oxidative addition of HCl or H2 to precursor insitu iridium(I) species are described. The complexes, trans, mer-IrHCl2(DMSO)3 (1a) and cis, mer-IrH2Cl(DMSO)3 (2), have been characterized by 1H nmr and ir, and contain only S-bonded sulphoxide, DMSO. Comparison is made with data for other isomers reported in the literature, and some discrepancies are discussed. The decomposition of 1a and 2 in chloroform leads to isomers of IrCl3(DMSO)3, while (2) with HCl generates cis,cis IrHCl2(DMSO)2(DMSO) with the O-bonded sulfoxide trans to hydride. The reaction of 1a in dichloromethane with dioxygen occurs with a 1:1 stoichiometry and generates two complexes tentatively formulated as Ir(OH)Cl2(DMSO)2H2O (3) and IrCl2(O2)(DMSO)2DMSO (4); a hydroperoxide intermediate (Ir—OOH) initially formed from 1a is considered to react with further 1a in the rate-determining step. Oxidation of coordinated DMSO to the sulphone is not observed, implying that such a catalyzed O2-oxidation reported earlier in aqueous 2-propanol proceeds via reaction of IrOOH with free DMSO, or else via free hydrogen peroxide.