21-telluraporphyrins.: 1.: Impact of 21,23-heteroatom interactions on electrochemical redox potentials, 125Te NMR spectra, and absorption spectra

meso-Tetraphenyl-21-chalcogenaporphyrins 4-6 (S, Se, and Te as 21-chalcogen atoms, respectively) and meso-tetraphenyl-21,23-dichalcogenaporphyrins 7-10 [(S,S), (Se,S), (Se,Se), and (Te,S) combinations as 21,23-chalcogen atoms, respectively] were prepared by condensation of the appropriate 2,5-bis(phenylhydroxymethyl)chalcogenophene 11 with (1) benzaldehyde, pyrrole, tetrachlorobenzoquinone (TCBQ), and boron trifluoride etherate for the preparation of 4-6 or (2) the appropriate 2,5-bis(1-phenyl-1-pyrrolomethyl)chalcogenophene 13, TCBQ, and boron trifluoride etherate for the preparation of 7-10. Electrochemical oxidation and reduction potentials were measured by cyclic voltammetry for 4-10 and indicated that oxidation of 21-telluraporphyrins 6 and 10 was more facile (more cathodic) than for the other analogues in the series and 10 was more readily oxidized than 6. The band I absorption maxima of 21-telluraporphyrins 6 and 10 were at shorter wavelengths than those of the corresponding analogues containing only sulfur and/or selenium chalcogen atoms. The extinction coefficients, epsilon, of the Soret bands of 6 and 10 were 7.6 x 10(4) and 7.2 X 10(4) M-1 cm(-1), respectively, which is significantly smaller than analogues 4, 5, and 7-9, which have corresponding values of >2 x 10(5) M-1 cm(-1). The Te-125 NMR spectrum of 6 gave a chemical shift of delta 834. Oxidation of 6 to oxotelluraporphyrin 12 gave a Te-125 NMR chemical shift of delta 1045. 21-Tellura-23-thiaporphyrin 10 gave a Te-125 NMR chemical shift of 6 1039, perhaps reflecting deshielding of the Te nucleus by the less than van der Waals contact with the S nucleus.