Abstract
A new porphyrin-based porous organic polymer (POP) with BET surface area ranging from 780 to 880 m2/g was synthesized in free-base form via the reaction of meso-tetrakis(pentafluorophenyl) porphyrin and a rigid trigonal building block, hexahydroxytriphenylene. The material was then metallated with Fe(III) imparting activity for Lewis acid catalysis (regioselective methanolysis ring-opening of styrene oxide), oxidative cyclization catalysis (conversion of bis(2-hydroxy-1-naphthyl)methanes to the corresponding spirodienone), and a tandem catalytic processes: an in situ oxidation-cyclic aminal formation-oxidation sequence, which selectively converts benzyl alcohol to 2-phenyl-quinazolin-4(3H)-one. Notably, the catalyst is readily recoverable and reusable, with little loss in catalytic activity.
Highlights
Fe(porphyrin) units are ubiquitous in biology, most notably as O2 binding centers in heme proteins and as defining cofactors for the cytochrome P450 family of enzymes, which are responsible for many catalytic oxidation reactions[31]
Degradation is most often bimolecular, with pairs of iron porphyrins forming catalytically inactive oxo-bridged dimers or porphyrin rings being mistaken for target substrates by other iron porphyrins
We reasoned that an additional example would perhaps yield different polymer pore or aperture sizes, different surface areas, and/or different pore volumes than found far for metalloporphyrin-based POPs
Summary
Fe(porphyrin) units are ubiquitous in biology, most notably as O2 binding centers in heme proteins and as defining cofactors for the cytochrome P450 family of enzymes, which are responsible for many catalytic oxidation reactions[31]. We reasoned that an additional example would perhaps yield different polymer pore or aperture sizes, different surface areas, and/or different pore volumes than found far for metalloporphyrin-based POPs. We were interested in examining further the potential catalytic utility of Fe(porphyrin) POPs for three specific oxidative and/or Lewis-acid-activated transformations, as outlined briefly below. Spirodienones are an attractive class of molecules obtainable by oxidative cyclization of calix[n]arenes (Fig. 1)[47]. Several reagents have been used to oxidize bis(2-hydroxy-1-naphthyl)methanes as a subunit of calix[n]arene to the corresponding spirodienones. These include phenyltrimethylammonium tribromide (PTMATB)47, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)[48], N-chloro reagents[49], Ph3Bi50 and nanoparticle-supported TEMPO51 (2,2,6,6-tetramethylpiperidine-oxyl). It would be desirable to catalyze their formation with less expensive catalysts and less toxic oxidants
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