Visible light-triggered hydride transfer from [Cp*Ir(bpy)(H)](+) (1) to organic acids and 1-methylnicotinamide (MNA(+)) is reported (Cp* = pentamethylcyclopentadienyl; bpy = 2,2'-bipyridine). A new thermochemical cycle for determining excited-state hydride donor ability (hydricity) predicted that 1 would be an incredibly potent photohydride in acetonitrile. Phototriggered H2 release was indeed observed from 1 in the presence of various organic acids, providing experimental evidence for an increase in hydricity of at least 18 kcal/mol in the excited state. The rate and product selectivity of hydride transfer to MNA(+) are photoswitchable: 1,4-dihydro-1-methylnicotinamide forms slowly in the dark but rapidly under illumination, and photolysis can also produce doubly reduced 1,4,5,6-tetrahydro-1-methylnicotinamide.

Three phosphorescent Ir and Ru complexes containing dicarboxylate functional groups have been doped into the framework of Zr 6 O 4 (OH) 4 (bpdc) 6 (UiO-67, bpdc ¼ para-biphenyldicarboxylate) to yield stable metal-organic frameworks (MOFs 1-3) which are highly porous with BET surface areas of 2568, 2292, and 1277 m 2 g À1 , respectively. The 3 MLCT phosphorescence of 1-3 can be effectively quenched by O 2 to provide an efficient method for oxygen detection.

The mechanism of photochemical formic acid dehydrogenation catalyzed by [Cp*Ir­(bpy)­(Cl)]+ (1, bpy = 2,2′-bipyridine) and [Cp*Ir­(bpy-OMe)­(Cl)]+ (1-OMe, bpy-OMe = 4,4′-dimethoxy-2,2′-bipyridine) is examined. The catalysts operate with good turnover frequency (TOF) across an unusually wide pH range. Above pH 7, the evolved gas is >95% pure H2 (along with traces of CO2 but no detectable CO). Light-triggered H2 release from a metal hydride intermediate is found to be the turnover-limiting step, based on the observed first-order dependence on catalyst concentration, saturation behavior in formate concentration, and direct in situ observation of a metal hydride resting state during turnover. Deactivation pathways are identified, including ligand loss and aggregate formation, precipitation of insoluble forms of the catalyst, and deprotonation of the iridium hydride intermediate. Guided by mechanistic insights, improved catalytic activity (initial TOF exceeding 50 h–1), stability (>500 turnovers at nearly 5 atm), and selectivity (>95% H2 gas) are achieved.

The innate H₂ evolution photochemistry of an iridium hydride complex is diverted towards photochemical hydrodechlorination of dichloromethane with high selectivity and quantum yield.