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

An ionic porous organic polymer ( TzTzIPOP )─synthesized from readily accessible 2,5-di(pyridine-4-yl)thiazolo[5,4- d ]thiazole ( BpyTzTz ) and 3,3′,5,5′-tetrakis(bromomethyl)-2,2′,6,6′-tetramethylbiphenyl ( TMBB ) as the building blocks using the Menshutkin reaction for polymerization─is shown to serve as an excellent heterogeneous photoredox as well as the photosensitizing catalyst in the presence of molecular oxygen. Efficient green and sustainable oxidation of arylmethylene compounds (C(sp 3 )–H bonds) and alcohols to carbonyl compounds is demonstrated under blue LED irradiation conditions of TzTzIPOP in the presence of molecular oxygen. Mechanistically, the oxidations proceed through photoinduced single-electron transfer as well as energy transfer processes involving the intermediacy of the superoxide anion (O 2 •– ) and singlet oxygen ( 1 O 2 ), respectively. The heterogeneous recyclable TzTzIPOP catalyst is shown to be robust enough to permit oxidation reactions multiple times (at least 10 cycles) without the loss of any catalytic activity. The oxidation reactions that proceed with molecular oxygen as an oxidant under heterogeneous conditions, facilitating easy workup, should be of much relevance to industrial processes.