Photoswitchable Thioureas for the External Manipulation of Catalytic Activity

Abstract

A series of azobenzene-based thiourea catalysts have been developed with the aim of achieving control over the catalytic activity by the use of light. The conceptual design of these systems relies on the inactivation by means of intramolecular hydrogen bonding, only likely to take place in one of their isomeric forms. After fine structure modulation of the catalyst a substantial difference in activity has been observed between the irradiated and the nonirradiated reaction. Furthermore, the system allowed in situ manipulation of the catalyst activity during the course of a given experiment.

Photoswitchable ring-opening polymerization of lactide catalyzed by azobenzene-based thiourea

“…17 Compound 1 has Z and E isomers, which can be mutually transformed easily by appropriate light irradiation. The E isomer of compound 1 has an open active site of thiourea group for the coordination of lactide via hydrogen bond interactions (Chart 1).…”

Intramolecular Hydrogen Bonds Enhance Disparity in Reactivity between Isomers of Photoswitchable Sorbents and CO2: A Computational Study

“…Moreover, from the experimental side, Pericàs and co-workers recently demonstrated that intramolecular Hb onds do not affect the photoisomerization of an azobenzene-derived thiourea organocatalyst. [52] 2.6. Light-Facilitated Capture Cycle Figure 7p resents as cheme of the work cycle of the photoswitchable CO 2 captures ystem.A tt he beginningo ft he cycle, the sorbentmolecule (e.g.…”

Bifunctional Molecular Photoswitches Based on Overcrowded Alkenes for Dynamic Control of Catalytic Activity in Michael Addition Reactions

“…The switchable catalyst was able to increase the yield of the reaction after 2 h (background, 27 %) from 37 %, using the less active state ( E )‐isomer, to 78 % yield using the more active ( Z )‐isomer. Pericás and co‐workers developed a switchable azobenzene‐thiourea organocatalyst, which was used to achieve control of Michael addition reactions through reversible hydrogen‐bond shielding of the catalytic unit, enabled by a nitro group as the blocking moiety . The ( E )‐isomer effectively catalysed the Michael addition of 2,4‐pentanedione to ( E )‐3‐bromo‐β‐nitrostyrene (full conversion was achieved after 19 h), whereas the photogenerated ( Z )‐isomer, in which the nitro group engages in hydrogen bonding interactions with the thiourea moiety, led to a significantly lower reaction rate (only 23 % conversion after 20 h).…”