Heterogeneous Catalytic Oxidations with In Situ-Generated Hypervalent Iodine-Based Porous Organic Polymers

Porous organic polymers (POPs) are novel emergent materials for heterogeneous organocatalysis owing to their remarkable physicochemical stabilities. Through a bottom-up approach entailing diligent design of twisted biaryl building blocks with in-built o-iodobenzoic acid (IA) moieties, a series of POP precatalysts, p-OMeIA-POP, DiMeIA-POP, and m-OMeIA-POP, were synthesized by employing Friedel-Crafts alkylation. These IA-POP precatalysts can undergo in situ oxidation in the presence of Oxone^® to generate hypervalent iodine(V) species (λ⁵-iodanes), in particular, modified o-iodoxybenzoic acid, popularly termed IBX, which mediates diverse oxidative transformations. The applications of m-OMeIA-POP as a heterogeneous precatalyst in the presence of Oxone^® are demonstrated for facile oxidation of i) primary and secondary alcohols to carbonyl compounds, ii) cleavage of olefins, vicinal diols, and acyloins into carboxylic acids and iii) oxidation of diols to lactones; the in situ formation of the λ⁵-iodane species in catalytic amounts precludes potential explosive attributes of IBX. It is shown that the IA-precatalyst (m-OMeIA-POP) can be easily recycled without any loss of catalytic activity. The results constitute the first demonstration of the development of IA-bearing POP precatalysts for in situ generation of hypervalent iodine(V) species and various heterogeneous oxidations mediated therefrom.