title: Bifunctional Molecular Photoswitches Based on Overcrowded Alkenes for Dynamic Control of Catalytic Activity in Michael Addition Reactions.
abstract: The emerging field of artificial photoswitchable catalysis has recently shown striking examples of functional light-responsive systems allowing for dynamic control of activity and selectivity in organocatalysis and metal-catalysed transformations. While our group has already disclosed systems featuring first generation molecular motors as the switchable central core, a design based on second generation molecular motors is lacking. Here, the syntheses of two bifunctionalised molecular switches based on a photoresponsive tetrasubstituted alkene core are reported. They feature a thiourea substituent as hydrogen-donor moiety in the upper half and a basic dimethylamine group in the lower half. This combination of functional groups offers the possibility for application of these molecules in photoswitchable catalytic processes. The light-responsive central cores were synthesized by a Barton-Kellogg coupling of the prefunctionalized upper and lower halves. Derivatization using Buchwald-Hartwig amination and subsequent introduction of the thiourea substituent afforded the target compounds. Control of catalytic activity in the Michael addition reaction between (E)-3-bromo-β-nitrostyrene and 2,4-pentanedione is achieved upon irradiation of stable-(E) and stable-(Z) isomers of the bifunctional catalyst 1. Both isomers display a decrease in catalytic activity upon irradiation to the metastable state, providing systems with the potential to be applied as ON/OFF catalytic photoswitches.
authors.affiliation: Centre for Systems Chemistry, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands.
authors.forename: Stefano F
authors.initials: SF
authors.lastname: Pizzolato
authors.affiliation: Centre for Systems Chemistry, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands.
authors.forename: Beatrice S L
authors.initials: BSL
authors.lastname: Collins
authors.affiliation: Centre for Systems Chemistry, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands.
authors.forename: Thomas
authors.initials: T
authors.lastname: van Leeuwen
authors.affiliation: Centre for Systems Chemistry, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands.
authors.forename: Ben L
authors.initials: BL
authors.lastname: Feringa
keywords: Michael addition; activity control; molecular switches; photochemistry; photoswitchable catalysts