New five-co-ordinate thiocarbonyl complexes [Ir(CO)2(CS)L2]X (L = PPh3 or PCy3, Cy = cyclohexyl; X = BPh4 or ClO4), [Ir(CO)(CS)(PMePh2)3]BPh4, [Ir(CS)(diphos)2]BPh4, and [IrCl(NO)(CS)L2]BF4 are reported. These complexes have been synthesised from trans-IrCl(CS)L2, by routes similar to those used in the preparation of their carbonyl analogues, with which they are compared and contrasted. [Ir(CO)2(CS)(PPh3)2]ClO4 does not react with hydrogen in solution, while [Ir(CO)2(CS)(PCy3)2]ClO4 reacts to give the dihydride [IrH2(CO)(CS)(PCy3)2]ClO4. Passage of CO through a solution of the latter, regenerates the original pentaco-ordinated iridium(I) complex, and the lability of the co-ordinated hydrogen is confirmed by its ready exchange with deuterium, to give the dideuteride. The reaction of [Ir(CO)2(CS)(PPh3)2]ClO4 with methoxide ion proceeds by nucleophilic attack at a carbonyl group, rather than at the thiocarbonyl group, to give Ir(CO2Me)(CO)(CS)(PPh3)2.