Directing two azo-bridged covalent metalloporphyrinic polymers as highly efficient catalysts for selective oxidation

Manganese meso-tetra (4-nitrophenyl)porphyrin (Mn-TNPP) with four nitro groups at periphery was employed as building moieties to condense with p-phenylenediamine and benzidine into extended π materials, respectively. Two covalent metalloporphyinic polymers (CMPs) linked by azo (-N=N-) were denoted as azo-CMP-1 and azo-CMP-2. FT-IR, XRD, SEM, TG, contact angle (CA) and XPS were used to analyze and characterize the synthesized heterogeneous materials. The catalytic study has demonstrated that azo-CMP catalysts displayed an excellent performance for epoxidation of olefins, especially cyclohexene. When azo-CMP-1 was recycled five times, its catalytic activity remained with an inconspicuous decrease. Additionally, azo-CMP series exhibited a amphipathic property evidenced by CA test, facilitating the diffusion of reactant into channels of azo-CMPs. Furthermore, the peak value of Mn2p3/2 shifting to a higher value for azo-CMP-1 suggested that there was a catalysis-promoted electronic environment around the Mn(III) active sites, compared to either azo-CMP-2 or homogenous sites.