Porphyrin Dendrimers Research Articles

Shape selective epoxidation of alkenes by metalloporphyrin-dendrimers

A series of oxidatively robust manganese-porphyrin-dendrimers were synthesized in good yields for use as shape-selective oxidation catalysts. The poly(phenylester) dendrimers with the bulky tert-butyl terminal groups were synthesized with a convergent approach. These cascade dendrimers were linked at the meta-phenyl positions of the 5,10,15,20-tetrakis(3′,5′-dihydroxyphenyl)porphinato manganese(III) chloride to produce a sterically hindered metal center. The regioselectivity of these catalysts was determined for epoxidation of non-conjugated dienes and 1:1 intermolecular mixture of linear and cyclic alkenes using iodosylbenzene as the oxygen donor. Metalloporphyrin dendrimers exhibit significantly higher substrate selectivity compared to unsubstituted Mn(TPP)(CI), but only moderate selectivity relative to the extremely hindered bis-pocket porphyrin, 5,10,15,20-tetrakis(2′,4′,6′-triphenylphenyl)porphinato manganese(III) acetate. Molecular modeling was performed on the porphyrin dendrimers to elucidate the extent of steric crowding around the porphyrin. There is a relatively large cavity for substrate entrance in the manganese-porphyrin-dendrimers relative to extremely hindered bis-pocket porphyrin.