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 IrCl- (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. π-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.
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