Reactions of allyl- and propadienyl-rhodium(III) and -iridium(III) complexes with polyhalogenomethanes. Rhodium(II) and iridium(II) species as reactive intermediates

Abstract

Several allylcarbonyldihalogenobis(phosphine)-rhodium(III) and -iridium(III) complexes react with CBrCl₃, to give the carbonyltrihaIogenobis(phosphine)meta!(III) complex and 4,4,4-trichlorobut-1 -ene. More highly substituted allyldihalogenobis(phosphine)-rhodium(III) and -iridium(III) complexes give mixtures of the corresponding tri-chlorobutene and ally1 halide. Carbonyldihalogenobis(phosphine)propadienyl-rhodium(III) and -iridium(III) complexes give the 4,4,4-trichlorobut-1 -yne either as the sole organic product or mixed with the corresponding organic halides. By analogy with reactions of allyl- and propadienyl-cobaloximes, it is suggested that the tri-chlorobutenes and trichlorobutynes are formed by a chain reaction involving two steps, the displacement of a five-co- ordinate rhodium(II) or iridium(II) complex by regiospecific attack of trichloromethyl radicals on the γ-carbon of the allyl or propadienyl group and the formation of trichioromethyl radicals by reaction of the rhodium(II) or iridium(II) complex with CBrCl₃. The organic halide is formed by a concurrent ionic reductive elimination sup-ported by capture of the rhodium(I) or iridium(I) product by CBrCl₃.