The dehydrogenation of IrH 2 {C 6 H 3 -2,6-(CH 2 PBu t 2 ) 2 } (1) by tert-butylethylene followed by reaction with an excess of water leads to the isolation of IrH(OH){C 6 H 3 -2,6-(CH 2 PBu t 2 ) 2 } (2) in nearly quantitative yield. The hydrido hydroxo complex has been characterized by multinuclear NMR spectroscopy as well as a single-crystal X-ray structure determination. An isotopic labeling study with D 2 O indicates that 2 arises from the oxidative addition of water to the intermediate 14-electron complex Ir{C 6 H 3 -2,6-(CH 2 PBu t 2 ) 2 }. The title complex is an efficient catalyst for the transfer dehydrogenation of cyclooctane to cyclooctene but shows no catalytic activity for the hydroxylation of the alkane by water. The conversion of 1 to 2 can be reversed by placing a solution of 2 under 1 atm of H 2 at 25 °C.