Halide redistribution reactions of rhodium(III) and iridium(III) complexes of the type mer-[MX 3(PMe 2Ph) 3] (X = Cl or I)

Abstract

Halide exchange between mer-[RhCl 3L 3] and mer-[RhI 3L 3] (L=PMe 2Ph) in chloroform at room temperature gives an equilibrium mixture of these two compounds and one specific isomer each ( trans, mer) of [RhCl 2IL 3] and [RhClI 2L 3] such that there is an approximately equal quantity of each species in solution after several hours. This exchange is catalysed by the aqua-complex [RhCl 2(H 2O)L 3][ClO 4] or by [(Ph 3P) 2N]Cl {[PPN]Cl}. The mechanism of exchange catalysed by the aqua-complex involves halide transfer via intermediates of the type [L 3X 2RhXRhX 2L 3] + (X=Cl or I). Transfer is very rapid, rapid enough to give total 1H NMR coalescence of PMe 2Ph signals in mixtures of [RhCl 3L 3] and [RhCl 2(H 2O)L 3] [ClO 4]. A further uncatalysed halide exchange occurs slowly to give a mixture of [RhCl 3L 3], [RhI 3L 3], and both possible isomers ( trans,mer and cis,mer) of the two mixed halide complexes. The composition of the equilibrium mixture indicates a six-fold preference for chloride over iodide in the labile site trans to PMe 2Ph. Possible mechanisms for this slow process are discussed. With iridium only the first process occurs at measurable rates.