Formation and properties of some chlorocarbonyl complexes of rhodium(I) in aqueous solution

Abstract

Carbon monoxide reduces aqueous hydrochloric acid solutions of RhCl₃,3H₂O under mild conditions to the dichlorodicarbonylrhodate(I) species, [Rh(CO)₂Cl₂]^–, in an autocatalytic reaction. The kinetics indicate that reduction occurs via direct reaction of carbon monoxide with [RhCl₅(OH)]^2– and possibly [RhCl₅(H₂O)]^2–, followed by a more efficient sequence involving formation of mixed valence Rh^III⋯ Rh^I bridged intermediate. The carbon monoxide is effectively being activated by co-ordination to rhodium, and iron(III) has been catalytically reduced using the carbon monoxide–dichlorodicarbonylrhodate(I) system.

At room temperature carbon monoxide rapidly converts fresh aqueous solutions of RhCl₃,3H₂O to the [RhCl₂(H₂O)₄]⁺ species via a similar bridge mechanism involving small amounts of chlororhodate(I) species.