Evidence for the Intervention of Different C−H Activating Intermediates in the Irradiation of (η5-C5Me5)(PMe3)IrH2 and the Reaction of (η5-C5Me5)(PMe3)Ir(H)(Cl) with Strong Base. Detection and Spectroscopic Characterization of (η5-C5Me5)(PMe3)Ir(Li)(Cl), an Intermediate in the Dehydrohalogenation Reaction

Abstract

Reaction of (η5-C5Me5)(PMe3)Ir(H)(X) (X = Cl, Br) with tert-butyllithium in hydrocarbon solvent results in dehydrohalogenation of the iridium center and subsequent C−H bond activation of solvent to give (η5-C5Me5)(PMe3)Ir(R)(H) (R = Ph, cyclohexyl, cyclooctyl). Low-temperature 1H, 31P, and 7Li NMR studies indicate that the dehydrohalogenation reaction occurs via the formation of the intermediate (η5-C5Me5)(PMe3)Ir(Li)(X). Competition experiments involving C−H bond activation in benzene−cyclohexane−cyclooctane mixtures have allowed for the determination of a relative intermolecular selectivity scale for these substrates. The selectivities (reported on a per hydrogen basis) for benzene, cyclooctane, and cyclohexane C−H bond activation were found to be 4.98:0.74:1, respectively, and are significantly different from those obtained via photoinduced dihydrogen elimination from (η5-C5Me5)(PMe3)IrH2. Further, when Bronsted bases other than tert-butyllithium were employed, the intermolecular selectivities in the b...