Efficient Homogeneous Hydridoirida‐β‐Diketone‐Catalyzed Methanolysis of Ammonia‐Borane for Hydrogen Release in Air. Mechanistic Insights

The hydridoirida-β-diketone [(IrH{(PPh2(o-C6H4CO))2H})2(μ-Cl)][BF4] (2) has been used as a homogeneous catalyst for the methanolysis of ammonia-borane to release up 3 equivalents hydrogen in presence air. With loadings low 0.2 mol%, undergoes within 6 min at 30 °C, with TOF50% 320 molH2 ⋅ molIr−1 min−1, or 80 s 60 an excellent 1991 and maintains its catalytic activity consecutive runs. Triethylamine-borane fails undergo methanolysis. Kinetic studies indicate first-order dependence on substrate concentration suggest cleavage solvent O−H bond being involved rate determining step reaction. In methanol solution 2 forms cationic [IrH(MeOH){(PPh2(o-C6H4CO))2H}]+ (3) reacts Me3N−BH3 afford [IrH(Me3NBH3){(PPh2(o-C6H4CO))2H}]+ (4), borane adduct η1-coordinated iridium. Compound [4][BArF4] shows dynamic behaviour due exchange bridging terminal B−H bonds. A multinuclear NMR study catalyzed reaction formation two ammonia-methoxyborane intermediates, H3N−BH2(OCH3) H3N−BH(OCH3)2, iridium species proposed hydridodiacyl type [IrH(H3NBH3−x(OCH3)x)(PPh2(o-C6H4CO))2] coordinated adduct. On account experimental evidence, simplified cycle is suggested AB hydrogen.