title: Photoswitchable hydride transfer from iridium to 1-methylnicotinamide rationalized by thermochemical cycles.
abstract: 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.
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599-3290, United States.
authors.forename: Seth M
authors.initials: SM
authors.lastname: Barrett
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Pitman
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Walden
authors.forename: Alexander J M
authors.initials: AJ
authors.lastname: Miller
mesh_terms: D006859:Hydrogen / Q000737:chemistry*; D007495:Iridium / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009536:Niacinamide / Q000031:analogs & derivatives* / Q000737:chemistry; D055668:Photochemical Processes; D013696:Temperature
chemical_list: D009536:Niacinamide; D007495:Iridium; D006859:Hydrogen; C024058:N(1)-methylnicotinamide