title: Sunlight-driven copper-catalyst activation applied to photolatent click chemistry.
abstract: The synthesis, full characterization, photoreduction properties, and catalytic activity for the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction of a copper(II)-DMEDA (N,N'-dimethylethylendiamine) complex is reported. Spectroscopic studies (UV/Vis, EPR) demonstrated that under daylight illumination highly effective copper(II) to copper(I) reduction occurs in this complex. These findings are in agreement with a high photoreduction quantum yield value of 0.22 in MeOH, and a value approaching unity as determined in THF. The reduction process, which can also be conducted by irradiation at 365 nm by using a standard TLC (thin layer chromatography) lamp, is ascribed to a highly efficient photoinduced electron transfer (PET) process mediated by the benzophenone photosensitizer present in the carboxylate counterion. Having deaerated the reaction mixture, the photogenerated copper(I) species proved to be highly active for the CuAAC reaction, demonstrated by reactions conducted with low catalyst loading (0.5 mol %) on a range of clickable protected and non-protected mono- and disaccharides. Once initiated, the reaction can be stopped at any time on introducing air into the reaction medium. Deoxygenation followed by irradiation restores the activity, making the copper(II)-DMEDA complex a switchable catalyst of practical value.
authors.affiliation: Université de Bordeaux, Institut des Sciences Moléculaires UMR-CNRS 5255, 351, Crs de la Libération, 33405 Talence Cedex (France).
authors.forename: Rédouane
authors.initials: R
authors.lastname: Beniazza
authors.forename: Romain
authors.initials: R
authors.lastname: Lambert
authors.forename: Lydie
authors.initials: L
authors.lastname: Harmand
authors.forename: Florian
authors.initials: F
authors.lastname: Molton
authors.forename: Carole
authors.initials: C
authors.lastname: Duboc
authors.forename: Sergey
authors.initials: S
authors.lastname: Denisov
authors.forename: Gedeminas
authors.initials: G
authors.lastname: Jonusauskas
authors.forename: Nathan D
authors.initials: ND
authors.lastname: McClenaghan
authors.forename: Dominique
authors.initials: D
authors.lastname: Lastécouères
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Vincent
keywords: benzophenone; click chemistry; copper catalysts; photoactivation; photoinduced electron transfer