Dehydrogenation of Dimethylamine-Borane Catalyzed by Half-Sandwich Ir and Rh Complexes: Mechanism and the Role of Cp* Noninnocence

Half-sandwich Cp*Rh-III complexes (Cp* = eta(5)-1,2,3,4,5-pentamethylcydopentadienyl) supported by 2,2'-bipyridine or 4,4'-di-tert-butyl-2,2'-bipyridine catalyze dehydrogenation of dimethylamine borane (Me2NH center dot BH3) to produce H-2 and dimethylamino borane dimer (Me2N-BH2)(2) with turnovers of 2200. The Ir-III analogues, on the other hand, display dramatically poorer catalytic activity. Mechanistic inferences drawn from stoichiometric reactions and DFT calculations suggest noninnocent involvement of the Cp* moiety as a proton shuttle.