Porphyrin Capped with Calix[4]arene Derivative via Hydrogen Bonds

A calix[4]arene–porphyrin duplex was prepared by mixing equimolar amounts of hydroxy or carboxy calix[4]arene derivatives and pyridyl or o-aminophenylporphyrin derivatives. Electrospray ionization mass spectrometry (ESI-MS) was applied to screen a suitable pair of a calix[4]arene and a porphyrin. meso-Tetra(2-pyridyl)porphyrin formed a duplex with tetrahydroxy or tetrahydroxymethylcalix[4]arene via triple or quadruple hydrogen bonds. 1H NMR spectra showed that the tetrahydroxycalix[4]arene was symmetrically located upon the porphyrin ring, whereas trihydroxycalix[4]arene was slanted on the porphyrin ring. The duplex of meso-tetra(2-pyridyl)porphyrinatocobalt(II) and tetrahydroxymethylcalix[4]arene formed a complex with benzylimidazole, which was capable of reversible dioxygen-binding. The capping structure upon porphyrin provided by calix[4]arene raised the life-time of dioxygen-adduct compared with the porphyrin without calix[4]arene.