1,2,5-Thiadiazolo[3,4-b]pyrazine-5,6-dicarbonitrile and derived porphyrazines: synthesis and electrochemical study

1,2,5-Thiadiazolo[3,4-b] pyrazine-5,6-dicarbonitrile, obtained by reaction of 5,6-diaminopyrazine-2,3-dicarbonitrile with SOCl2, exhibits strongly electron-deficient properties and easily forms reduced species (the reduction potentials -0.01 and -1.02 V in MeCN vs Ag/AgCl). Template cyclotetramerization in the presence of Mg butoxide in n-butanol and with indium(III) chloride in 1,2,4-trichlorobenzene affords the corresponding complexes of tetrakis(1,2,5-thiadiazolo[3',4':5,6] pyrazino)[2,3-b, g, l, q] porphyrazine, [(TSN(2)PyzPA)M] (M = Mg(H2O), InCl). The Mg(II) complex is characterized by a Q-band at 657 and a Soret band at 370 nm (in DMSO) and shows three reduction processes at -0.38, -0.83 and -1.21 V vs Ag/AgCl in DMSO.