The interaction of the complex H2Ir(CO)Cl(PPh3)(2) with various proton donors of increasing acidity, namely 2,2,2-trifluoro ethanol (TFE), 1,1,1,3,3,3-hexafluor-2-propanol (HFIP), perfluoro tert-butylalcohol (PFTB) and trifluoroacetic acid (TFA), has been investigated. The gradual proton downfield shift of the hydride trans to the chlorine, in the presence of increasing amounts of the proton donors, and the T-1 measurements have shown that the chlorine ligand is the basic counterpart in the hydrogen bond interaction. This intermolecular hydrogen bond influences the reactivity of the complex and particularly the H-2/D-2 exchange process. The HDIr(CO)Cl(PPh3)(2) isotopomer obtained by reacting H2Ir(CO)Cl(PPh3)(2) with D-2 in dichloromethane is formed in greater amount when one of the proton donors is added to the reaction mixture; furthermore the stronger the acid, the larger the amount of HDIr isotopomer formed. (C) 2003 Elsevier Science B.V. All rights reserved.