Macrocyclization of cyclic thiosemicarbazones with mercury salts

A new cyclic Schiff base L1H3 derived from benzil and thiosemicarbazide has been prepared in the presence of NaBH4. Reactions of the new molecule and the cyclic 5-methoxy-5,6-diphenyl-4,5-dihydro-2H-[1,2,4]triazine-3-thione L2H2 with mercury chloride and nitrate are reported. Complexes of 1:2 stoichiometry are obtained from L1H3, but the reactions from L2H2 yield complexes of the macrocyclic Schiff base 5,6,11,12-tetraphenyl-1,2,4,7,8,10-hexaaza-cyclododeca-4,6,10,12-tetraene-3,9-dithione L3H2, which indicates the macrocyclization of L2H2. A mechanism for the cyclization reaction based on the rupture of the C–N single bond in L2H2 is proposed. The electrochemical results of complex L3Hg makes it and its precursors, L2H2 and L3H2, outstanding candidates for mercury determination by appropriate electrode modification.