Abstract
Abstract Photocatalysis constitutes an important research interest due to its capability for achieving important chemical reactions in an environmentally green and sustainable manner. The use of heterogeneous photocatalysts adds additional advantages such as ease of separation from reaction mixtures, reusability, as well as photo, thermal and chemical stability. In this account, we showed how the surface complexation of different key players on TiO2 can be used control the reaction pathway to enable difficult organic transformations, as demonstrated by the selective aerobic oxidation of sulfides to sulfoxides. First, we designed a photocatalytic-surface complexation system comprising three fundamental components; visible-light-absorbing dye, TiO2 and TEMPO as the redox mediator. Next, the said system was elegantly simplified into a visible-light-harvesting surface complex generated in-situ between TiO2 and tertiary amines, which enabled O2 to be selectively activated only in the presence of the target sulfide substrate. This was then expanded into the new concept of synergistic photocatalysis, which is based on the interplay of reactants (sulfides and benzylamines) via the aforementioned visible-light-harvesting surface complex to enable two seemingly irrelevant reactions in one photocatalytic system. Lastly, we briefly discussed how surface complexation on heterogeneous catalysts such as metal oxides can be further utilized for photocatalytic organic transformations.
Highlights
Photocatalytic organic transformations have attracted considerable attention as a promising strategy for sustainable technological development.14 Through photocatalysis, many important chemical transformations can be achieved under mild conditions via the excitation of a photocatalyst with visible light, which initiates the subsequent radical reaction.57 A subset of photocatalysis, heterogeneous photocatalysis, is of particular interest due to advantages such as ease of separation from reaction mixtures, reusability, as well as photo, thermal and chemical stability.7 A large variety of heterogeneous materials have been developed for photocatalytic organic transformations,5 ranging from metal oxides such as Nb2O58 andBull
This can be expanded into the new concept of synergistic photocatalysis, which is based on the interplay of reactants via the aforementioned visible-light-harvesting surface complex to enable two seemingly irrelevant reactions in one photocatalytic system
We have reviewed how the surface complexation of different key players on TiO2 can be used to control the reaction pathway and enable difficult organic transformations, as demonstrated by the selective aerobic oxidation of sulfides to sulfoxides
Summary
Photocatalytic organic transformations have attracted considerable attention as a promising strategy for sustainable technological development.14 Through photocatalysis, many important chemical transformations can be achieved under mild conditions via the excitation of a photocatalyst with visible light, which initiates the subsequent radical reaction.57 A subset of photocatalysis, heterogeneous photocatalysis, is of particular interest due to advantages such as ease of separation from reaction mixtures, reusability, as well as photo, thermal and chemical stability. A large variety of heterogeneous materials have been developed for photocatalytic organic transformations, ranging from metal oxides such as Nb2O58 and. The conduction band of TiO2 can activate O2 for the selective aerobic photocatalytic oxidation of organic substrates, such as that of benzylamines to imines, benzylalcohols to benzaldehydes, and cyclohexane to cyclohexanone.20 This renders the chemical transformations environmentally friendly and sustainable. Having grasped an understanding of the crucial components of the photocatalytic system, the said system can be elegantly simplified into a visible-light-harvesting surface complex that is generated in-situ between TiO2 and tertiary amines that enables O2 to be selectively activated only in the presence of the target sulfide substrate.. We demonstrate a highly efficient photocatalytic-surface complexation system of three fundamental components; visible-lightabsorbing dye, TiO2 and TEMPO as the redox mediator. Having grasped an understanding of the crucial components of the photocatalytic system, the said system can be elegantly simplified into a visible-light-harvesting surface complex that is generated in-situ between TiO2 and tertiary amines that enables O2 to be selectively activated only in the presence of the target sulfide substrate. This can be expanded into the new concept of synergistic photocatalysis, which is based on the interplay of reactants (sulfides and benzylamines) via the aforementioned visible-light-harvesting surface complex to enable two seemingly irrelevant reactions in one photocatalytic system. Lastly, we will provide a brief discussion on how surface complexation on heterogeneous catalysts such as metal oxides can be further utilized for photocatalytic organic transformations
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