Charge-transfer Interactions between Sulfur Dioxide and Group 8 Half-sandwich Complexes

M ulliken-type charge-transfer complexes have been formed between basic half-sandwich compounds and SO, when [M(q5-C,R,)(CO),] (M = Rh or Ir; R, = Me,, H, or H,CF,), [Ir(q5-C,H,)(CO)(C,H,)]. and [M(q5-C,H,)(C,H,),] (M = Co, Rh or Ir) are isolated in SO,-doped argon matrices at 20 K; the v(C0) bands of the complexes are shifted to high frequency of those of the precursor molecules and prominent charge-transfer bands are observed; the same species have been detected when the compounds [M(q5-C,Me,)(CO),] (M = Rh or Ir) are embedded in polyethylene discs and treated with SO, at 213-298 K; the enthalpy of complexation of [Ir(q5-C,Me,)(CO),] with SO, is -13 f 3 kJ mo1V