meso-Thiaporphyrinoids Revisited: Missing of Sulfur by Small Metals

Facile synthesis of meso-aryl-substituted 5,15-dithiaporphyrins and 10-thiacorroles has been achieved by sulfidation of a,a'-dichlorodipyrrin metal complexes with sodium sulfide in DMF. Thiacorrole metal complexes exhibit distinct aromaticity due to 18?p-conjugation including the lone pair on sulfur, whereas dithiaporphyrins are nonaromatic judging from 1H NMR spectra, X-ray analysis, and absorption spectra. We have found that NiII and AlIII dithiaporphyrin complexes undergo smooth thermal sulfur extrusion reaction to give the corresponding thiacorrole complexes, whereas free base, ZnII, PdII, and PtII dithiaporphyrin complexes did not exhibit the similar reactivity. The DFT calculations have elucidated a reaction pathway involving an episulfide intermediate, which can explain the markedly different reactivity among dithiaporphyrin metal complexes.