Oxidative addition of monosilanes to planar iridium(I) complexes and carbonylation of the resulting adducts

Abstract

Silanes [R₃SiH; R₃ = Cl₃, MeCl₂, (EtO)₃, Ph₃] undergo irreversible oxidative addition to planar iridium(I) complexes IrClL₃ (L = PPh₃, PMePh₂ or AsPh₃) to give silyliridium(III) hydrides IrHCl(SiR₃)L_n (n = 2 or 3). The yellow, five-coordinate, probably tetragonal pyramidal complexes(n = 2) are formed mainly when L = PPh₃ or AsPh₃, and also in the case of L = PmePh₂, R = Ph, whereas the colourless, six-coordinate, presumably octahedral adducts are formed predominantly when L = PMePh₂. Both five- and six-coordinate adducts can be isolated from the addition of dichloro(methyl)silane to IrCl(AsPh₃)₃. Most of the adducts react with carbon monoxide under ambient conditions to give silyliridium(III) hydrido carbonyls, IrHCl(SiR₃)(CO)L₂, which may undergo partial or complete reductive elimination to IrCl(CO)L₂ and R₃SiH; the ease with which this occurs depends on L (PPh₃ > PMePh₂ > AsPh₃) and on R₃ [Ph₃ > (EtO)₃ > Cl₃ ≈ MeCl₂]. The reactions of silanes with IrClL₃, RhClL₃ and IrCl(CO)(PPh₃)₂ are compared, and the trends observed in the case of IrClL₃ are discussed in terms of electronic and steric effects in the silyl and Group 5 donors. Structural assignments for the new complexes are based on i.r., far-i.r. and ¹H N.M.R. data.