The solution behaviour of [Rh2(COMe)2(CO)2I6]2–, its reactions with CO, pyridine, and methanol, and the X-ray structure of [AsPh4][Rh(COMe)(CO)(NC5H5)I3]

Abstract

It has been shown that the ion [Rh₂(COMe)₂(CO)₂I₆]^2– in CD₂Cl₂ consists of at least six species. However, in methanol it is probably present as [Rh(COMe)(CO)(MeOH)I₃]^–. The nature of these species is discussed. Carbon monoxide reacts reversibly with this compound to give mer-trans-[Rh(COMe)(CO)₂I₃]^2–. The trans arrangement of the carbonyl ligands has been demonstrated by ¹³CO–¹³CO coupling in an enriched sample at –130 °C, when rotation about the Rh–COMe bond is slow. The lack of carbonyl scrambling in [Rh₂(¹³COMe)₂(¹²CO)₂I₆]^2– demonstrates the irreversibility of its formation from [RhMe(CO)₂I₃]^–. Treatment of [Rh₂(COMe)₂(CO)₂I₆]^2– with pyridine generates a species, probably [I₃(OC)(MeCO)Rh(µ-I)Rh(COMe)(CO)(NC₅H₅)I₂]^2–, on slow addition and [AsPh₄][Rh(COMe)(CO)(NC₅H₅)I₃] on rapid addition. The latter compound was characterised by X-ray crystallography.