A SPECTROSCOPIC STUDY OF HALOCARBONYL COMPLEXES OF RHODIUM(I) AND RHODIUM(III)

NMR studies (C-13 and Rh-103) show that mixing of equimolar amounts of [RhX(2)(CO)(2)](-) and [RhY2(CO)(2)](-) (X not equal Y = Cl, Br, or I) results in approximately statistical X/Y exchange to give cis-[RhXY(CO)(2)](-). Products resulting from the addition of X(2) to [RhX(2)(CO)(2)](-) (X = Cl, Pr, or I) have been characterized by NMR and IR spectroscopic studies, and include the anions cis- and trans-[RhX(4)(CO)(2)](-) which slowly lose CO to give the bis(halogen)-bridged dimer [Rh(2)X(8)(CO)(2)](2-); the dimer progressively reacts with halide to give the mono(halogen)-bridged dimer [Rh(2)X(9)(CO)(2)](3-), and this is followed by the formation of [RhX(5)(CO)](2-). The tendency for replacement of the halide trans to CO by methanol increases in the order X = Cl < Br < I.