21-telluraporphyrins. 3. Synthesis, structure, and spectral properties of a 21,21-dihalo-21-telluraporphyrin

5,10-Diphenyl-15,20-di(4-methoxyphenyl)-21-telluraporphyrin (7) was prepared in 18% yield by the p-toluenesulfonic acid-catalyzed condensation of 2,5-bis(1-phenyl-1-hydroxymethyl)tellurophene (6), pyrrole, and 4-methoxybenzaldehyde in carefully deoxygenated CHCl3 followed by oxidation with p-chloranil. While H-1 and C-13 NMR spectra of 7 were consistent with a symmetrical molecule in solution, the X-ray crystal structure of 7 shows the pyrrole N-H on a pyrrole ring cis to the tellurophene and a planar porphryin core. Air oxidation of a CH2Cl2 solution of 7 under fluorescent lighting gave telluroxide 14. The reaction of a CH2Cl2 solution of 14 with 1 N HCl as a two-phase system gave 21,21-dichloro-21-telluraporphyrin 15. The X-ray structure of 15 indicated a distorted trigonal bipyramidal geometry around the Te atom with two chloride ligands occupying the axial positions. The Te atom and the N atom of the trans pyrrole were tipped out of plane in opposite directions to give a nonplanar porphyrin core. The Q-bands of the absorption spectra of 15 and "vacataporphyrin" 5 were similar, suggesting a similar aromatic structure in the two molecules.