Photoreduction of triplet thioxanthone derivative by azolium tetraphenylborate: a way to photogenerate N-heterocyclic carbenes

Abstract

The photochemical mechanism of a novel N-heterocyclic carbene (NHC) photogenerator is elucidatedviathe accurate identification of transient species and photoproducts.

Directing network degradability using wavelength-selective thiol-acrylate photopolymerization

“…S3A †). 54 The resulting TBD base deprotonates thiols to form thiolate anions, which then initiate the anion-mediated thiol-acrylate Michael addition reactions. This will result in a stoichiometric consumption of [SH] and [CvC] functional groups, eventually forming a thiolacrylate step-growth network crosslinked by dynamic disulfide bonds (Scheme 1).…”

Thioxanthone: a powerful photocatalyst for organic reactions

“…In 2019, Chemtob and coworkers reported the generation of Nheterocyclic carbenes (NHC) 24 from arylborate salts 112 and isopropyl thioxanthone 111. 98 Previous reports have shown that arylborate salts upon irradiation may act as electron donor in photoinduced electron transfer reaction (PET). Based on that, Chemtob and coworkers demonstrated that isopropylthioxanthone upon excitation can participate in an electron transfer event accepting an electron from boranyl anion, forming excited isopropylthioxanthone radical anion 113.…”

Photoinduced ring-opening polymerizations

“…They are usually composed of a chromophore counter anion and a protonated base (cation) and can be easily obtained: a) by direct reaction of a carboXylic acid functionalized chromophore with the base to be photogenerated, or b) by simple anions metathesis between the alkali salt of the chromophore unit and the halogen salt of the protonated base (Scheme 7). Two main types of counter anion chromophores have been employed in the field of photoROP: tetraphenylborate [46][47][48][49][50][51] and carboXylates [52,53]. In most cases, the mechanism of base photogeneration is based on the photodegradation of the chromophore counter anion to generate a carbanion that eventually abstracts a proton of the protonated base.…”

“…In order to extend their ab-sorption range, PBGs based on tetraphenylborate have often been associated with isopropopylthioXanthone (ITX) as photosensitizer (PS) [13]. However, in this case, generation of the base may occur through a different photomechanism, as reported by Trinh et al [50]. Yet, it proved particularly useful for the photogeneration of the NHCs 1,3-bis (mesityl)imidazol-2-ylidene (IMes) and 1,3-bis(mesityl)-4,5-dihydroimidazol-2-ylidene (SIMes) at 365 nm (Scheme 9) and their subsequent uses as ligands or as organocatalysts for ROP reactions [46,49].…”