Allyl chloride, 2-methylallyl chloride, or 2-chloroallyl chloride add cis to complexes of the type trans-[IrCl(CO)L2] where L = PMe2Ph or AsMe2Ph in benzene. In the adducts [IrCl2(σ-all)(CO)L2] the ligands L are mutually cis. These adducts isomerise in chloroform or ethanol and the isomers have the ligands L mutually trans. The isomerisation probably goes via a π-allylic cation [IrCl(π-all)(CO)L2]+ and such ions were isolated as their BPh4– or PF6– salts. These adducts [IrCl2(σ-all)(CO)L2] with trans-phosphines or -arsines can be prepared directly by treating trans-[IrCl(CO)L2] with the allylic chloride in methanol. Allyl bromide adds to trans-[IrCl(CO)(PMe2Ph)2] in benzene to give [IrBrCl(σ-allyl)(CO)(PMe2Ph)2] with mutually cis phosphines and bromide trans to phosphine. In ethanol bromide ion is solvolysed off to give [IrCl(π-allyl)(CO)(PMe2Ph)2]+Br– which then rearranges to [IrClBr(σ-allyl)(CO)(PMe2Ph)2] with trans-phosphines and bromide trans to the σ-allyl ligand. Other similar reactions are described. [IrCl(π-C3H5)(CO)(PMe2Ph)2]PF6 reacts with PMe2Ph to give [IrCl(σ-C3H5)(CO)(PMe2Ph)3]PF6. N.m.r. and i.r. data {ν(CO), ν(Ir–Cl) and ν(CC)} are given and discussed.