Triazine Frameworks for the Photocatalytic Selective Oxidation of Toluene

Abstract

Investigations into the selective oxidation of inert sp3 C–H bonds using polymer photocatalysts under mild conditions have been limited. Additionally, the structure–activity relationship of photocatalysts often remains insufficiently explored. Here, a series of thiophene‐based covalent triazine frameworks (CTFs) are used for the efficient and selective oxidation of hydrocarbons to aldehydes or ketones under ambient aerobic conditions. Spectroscopic methods conducted in situ and density functional theory (DFT) calculations revealed that the sulfur atoms within the thiophene units play a pivotal role as oxidation sites due to the generation of photogenerated holes. The effect of photogenerated holes on photocatalytic toluene oxidation was investigated by varying the length of the spacer in a CTF donor–acceptor based photocatalyst. Furthermore, the manipulation of reactive oxygen species was employed to enhance selectivity by weakening the peroxidative capacity. As an illustrative example, this study successfully demonstrated the synthesis of a precursor of the neurological drug AMG‐579 using a photocatalytic protocol.

Ionic Porous Organic Polymer as a Visible-Light Photocatalyst: Efficient Heterogeneous Oxidation of Arylmethylene Compounds and Alcohols Using Molecular Oxygen

“…Immobilization of photocatalysts/sensitizers in porous materials offers the advantage of conducting O 2 -mediated reactions in a heterogeneous phase in a recyclable fashion, obviating disposal of the catalyst at the end of the reaction. Several porous materials, e.g., covalent organic frameworks (COFs), covalent triazine frameworks, porous aromatic frameworks (PAFs), etc., constructed from building blocks like triazine, pyrene, porphyrin, thiophene, sulfone, etc., − have been exemplified as photocatalysts for applications which include water splitting, dye degradation, CO 2 reduction, and catalysis. − In particular, amorphous porous organic polymers (POPs), constructed by covalent polymerization of organic building blocks in a bottom-up fashion, , as photocatalysts are advantageous for the following reasons: (i) they are unrivalled for their physicochemical stabilities, (ii) their band gap energies and absorption in the visible region can be tuned by manipulating the structures of the monomeric building blocks to develop tailored-made materials for photocatalytic applications; (iii) their high surface areas, permanent porosity, and tunable pore size enable control over molecular diffusion and access of the reactants to catalytically active sites; (iv) they permit selectivity in catalytic oxidation reactions, cost-effectiveness, etc. Consequently, POPs have assumed prominence as inextricable materials for diverse applications over the past decade. − …”