ENCAPSULATION, STABILIZATION, AND CATALYTIC PROPERTIES OF FLEXIBLE METAL PORPHYRIN COMPLEXES IN MCM-41 WITH MINIMAL ELECTRONIC PERTURBATIONBY THE ENVIRONMENT

meso-Tetrakis(5-trimethylammoniopentyl)porphyrin (TMAP) was incorporat ed in MCM-41 directly during a hydrothermal synthesis or by a surfacta nt <-> porphyrin ion-exchange reaction with as-synthesized MCM-41. Bot h methods permitted encapsulation of the porphyrin within the mesoporo us channel system. UV-vis absorption spectra indicated that porphyrin molecules dimerized or formed larger agglomerates in the ion-exchanged samples, while TMAP molecules remained isolated in hydrothermally pre pared samples. Spectra of the latter samples closely resembled those o f TMAP in solution with no significant broadening of the Soret and Q-b and absorptions. Acid extraction of the surfactant converted the encap sulated free-base porphyrin to the dication TMAP-H-2(2+), which could be further metalated with Cu2+, Ni2+, Or Fe2+ without leaching porphyr in from the mesoporous sieve. The catalytic activity of the copper por phyrins was evaluated in the oxidative bleaching reaction of the azo d ye beta-naphthol violet. During this reaction, TMAP-Cu2+ also degraded when it was free in solution or incorporated in MCM-41 by ion exchang e. However, in samples where the porphyrin was directly incorporated d uring the hydrothermal synthesis, TMAP-Cu2+ was stabilized and exhibit ed greater catalytic activity for longer time periods. It is suggested that isolation of the porphyrin molecules within the MCM-41 channels prevented their mutual oxidation.