21-Telluraporphyrins. 1. Impact of 21,23-Heteroatom Interactions on Electrochemical Redox Potentials, <sup>125</sup>Te NMR Spectra, and Absorption Spectra

<i>meso</i>-Tetraphenyl-21-chalcogenaporphyrins <b>4</b>−<b>6</b> (S, Se, and Te as 21-chalcogen atoms, respectively) and <i>meso</i>-tetraphenyl-21,23-dichalcogenaporphyrins <b>7</b>−<b>10</b> [(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 <b>11</b> with (1) benzaldehyde, pyrrole, tetrachlorobenzoquinone (TCBQ), and boron trifluoride etherate for the preparation of <b>4</b>−<b>6</b> or (2) the appropriate 2,5-bis(1-phenyl-1-pyrrolomethyl)chalcogenophene <b>13</b>, TCBQ, and boron trifluoride etherate for the preparation of <b>7</b>−<b>10</b>. Electrochemical oxidation and reduction potentials were measured by cyclic voltammetry for <b>4</b>−<b>10</b> and indicated that oxidation of 21-telluraporphyrins <b>6</b> and <b>10</b> was more facile (more cathodic) than for the other analogues in the series and <b>10</b> was more readily oxidized than <b>6</b>. The band I absorption maxima of 21-telluraporphyrins <b>6</b> and <b>10</b> 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 <b>6</b> and <b>10</b> were 7.6 × 10<sup>4</sup> and 7.2 × 10<sup>4</sup> M<sup>-1</sup> cm<sup>-1</sup>, respectively, which is significantly smaller than analogues <b>4</b>, <b>5</b>, and <b>7</b>−<b>9</b>, which have corresponding values of >2 × 10<sup>5</sup> M<sup>-1</sup> cm<sup>-1</sup>. The <sup>125</sup>Te NMR spectrum of <b>6</b> gave a chemical shift of δ 834. Oxidation of <b>6</b> to oxotelluraporphyrin <b>12</b> gave a <sup>125</sup>Te NMR chemical shift of δ 1045. 21-Tellura-23-thiaporphyrin <b>10</b> gave a <sup>125</sup>Te 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.