Synthesis and properties of 5,10,15,20-tetrakis[4-(alkoxysilyl)phenyl]porphyrins: an application of selective deprotection of benzaldehyde diethyl acetals in the presence of alkoxysilyl groups.

Selective deprotection of 4-(alkoxysilyl)benzaldehyde diethyl acetals 1a-1c in the two-solvent system of hydrochloric acid and chloroform gave 4-(alkoxysilyl)benzaldehydes 2a-2c in good yields. Under these conditions, undesired hydrolysis of the alkoxysilyl group was minimized. The reaction of benzaldehydes 2a and 2b with pyrrole in the presence of boron trifluoride diethyl etherate led to 5,10,15,20-tetrakis[4-(alkoxysilyl)phenyl]porphyrins 3a and 3b. The X-ray structural analysis showed that 3b has a planar porphyrin ring and shows typical structural features of porphyrin rings. Hydrolysis-condensation of 3a in the presence of a surfactant afforded a porphyrin-silica hybrid (PSH) as insoluble brown powder. The PSH was found to be amorphous and to consist of aggregated nonspherical micrometre-sized particles with rough surfaces. The PSH has mesopores, and the specific surface area is 330 m(2) g(-1) which increases to 810 m(2) g(-1) upon calcination.