Oxidative addition of aliphatic alcohols to (C8H14)IrCl(PMe3)(3) in benzene yields the cis-hydridoalkoxo products mer-cis-HIr(OR)Cl(PMe3)(3) (R = Me, Et, 1-pentyl, 2-propyl) The analogous hydroxo complex is prepared by oxidative addition of water in THF. The addition rate depends on the nature of the alcohol (methanol > 1-pentanol >> 2-propanol and methanol > water). The reaction is retarded in polar media but accelerated by protic cosolvents. Anionic ligand redistribution involving chloride and alkoxide (or hydroxide) competes with the oxidative addition reaction. A detailed kinetic study suggests that the 16-electron 10(PMe3)(3) is the species undergoing the oxidative addition, and mer-cis-HIr(OR)Cl(PMe3)(3) is the kinetic product. The reaction proceeds by a single-step nucleophilic attack of the metal on the O-H proton pi-Donation by chloride stabilizes the transition state and governs the stereochemical course of the reaction Protic solvent aggregation in the transition state in an apolar medium is suggested mer-cis-HIr(OH)Cl(PEt3)(3), obtained by water addition to IrCl(PEt3)(3), was crystallographically characterized, showing an unusual hydrophobic cage around the hydride ligand.