21-Telluraporphyrins. 1. Impact of 21,23-Heteroatom Interactions on Electrochemical Redox Potentials, 125Te NMR Spectra, and Absorption Spectra
journal contributionposted on 07.06.2002, 00:00 by Masako Abe, David G. Hilmey, Corey E. Stilts, Dinesh K. Sukumaran, Michael R. Detty
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, ∈, of the Soret bands of 6 and 10 were 7.6 × 104 and 7.2 × 104 M-1 cm-1, respectively, which is significantly smaller than analogues 4, 5, and 7−9, which have corresponding values of >2 × 105 M-1 cm-1. The 125Te NMR spectrum of 6 gave a chemical shift of δ 834. Oxidation of 6 to oxotelluraporphyrin 12 gave a 125Te NMR chemical shift of δ 1045. 21-Tellura-23-thiaporphyrin 10 gave a 125Te NMR chemical shift of δ 1039, perhaps reflecting deshielding of the Te nucleus by the less than van der Waals contact with the S nucleus.
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chemical shiftElectrochemical oxidationcyclic voltammetryabsorption maximareduction potentialsSoret bandsextinction coefficients125 Te NMR Spectra1. Impactδ 834. Oxidationoxotelluraporphyrin 12Electrochemical Redox Potentialsanalogues 4Te nucleusSeS nucleusTCBQ125 Te NMR spectrumAbsorption Spectra mesovan der Waals contactchalcogenboron trifluoride etherate125 Te NMR chemical shift