Highly Active Iridium(III)–NHC System for the Catalytic B–N Bond Activation and Subsequent Solvolysis of Ammonia–Borane
dataset
posted on 2011-10-24, 00:00 authored by George C. Fortman, Alexandra M. Z. Slawin, Steven P. NolanA series of coordinatively unsaturated NHC–Ir(III) complexes are examined in terms of their catalytic activity toward the solvolysis of ammonia–borane (AB). Utilization of [Ir(ItBu′)2Cl] (2) and [Ir(ItBu′)2][PF6] (3) at 50 ppm catalyst loading led to reactions evolving approximately 3 equiv of H2 within 10 min at 40 °C. The activation parameters of the reaction were measured to be ΔH⧧ = 11.1 kcal/mol and ΔS⧧ = 30.9 eu. Mechanistic investigations revealed an equilibrium between [Ir(H)(NH3)(ItBu)(ItBu′)][PF6] (4) + H2 and [Ir(H)2(ItBu)2][PF6] (6) + NH3. Spectroscopic data suggest that complexes 4 and 6 are the resting state of the active catalyst. X-ray structures of complex 4 and [Ir(NH3)(ItBu′)2][PF6] (5) are given.
