The preparation of [IrCl(CO)(C8H14)3] from chloroiridic acid and cyclo-octene reacting in an alcohol, e.g., ethanol, is described. The carbonyl ligand is formed by breakdown of the alcohol and methane is evolved when ethanol is used as reactant (solvent). On washing with ether this triscyclo-octene complex loses cyclo-octene to give [IrCl(CO)(C8H14)2]2. The cyclo-octene ligands can be readily displaced, e.g., by triphenylphosphine, diethylphenylphosphine, or hexa-1,5-diene. Allylic chlorides add on to the complex [IrCl(CO)(C8H14)2]2 with displacement of some cyclo-octene; e.g., with 2-methylallyl chloride the complex [IrCl2(C4H7)(CO)(C8H14)] is formed; this reacts with more strongly bonding neutral ligands such as pyridine, PPh3, AsPh3, etc., and the products [IrCl2(C4H7)(CO)L] contain asymmetrically bonded allylic groups. Acyl chlorides (RCOCl) react with [IrCl(CO)(C8H14)2]2 to give bridged chloro-complexes of the type [IrCl2R(CO)2]2(R = Me, Et, Pri, or Ph). The methyl compound has had its structure determined by X-ray diffraction. This methyl compound reacts with two mol. of dimethylphenylphosphine to give a binuclear acetyl complex [IrCl2(COMe)CO(PMe2Ph)]2 and with a further two mol. to give the mononuclear complex [IrCl2(COMe)CO(PMe2Ph)2] of known stereochemistry. In contrast, the methyl complex [IrCl2Me(CO)2]2 reacts with pyridine to give mixtures of isomers of type [IrCl2Me(CO)2Py], which are not acetyl complexes; similarly for the ethyl complex. The ethyl complex [IrCl2Et(CO)2py] when heated above its melting point evolves ethylene and pyridine to give bronze needles of what appears to be a hydrido-dicarbonyliridium complex, [IrHCl2(CO)2]x of unknown molecularity. This compound is more easily prepared by treating chloridic acid with carbon monoxide in boiling ethanol. The complex [IrCl(CO)(C8H14)2]2 takes up two mol. of ethylene per iridium atom reversibly; with more ethylene n.m.r. studies show that ethylene exchange between free and complexed ethylene, and also cyclo-octene exchange, is very rapid.