New vanadium mediated one-pot in situ (L)-histidine based ligand cyclization and aerobic dehydrogenative aromatization

This work reports a new one pot vanadium mediated cyclization and subsequent aerobic dehydrogenative aromatization of two (L)-histidine based ligands. Ligand cyclization results from the intra ligand CC bond formation between C(sp2) of (L)-histidine imidazolyl ring and the imine C-H. [Display omitted] •In-situ V(V) mediated cyclization and aerobic dehydrogenative aromatization of (L)-histidine based ligands in one-pot method.•It leads to the formation of two new dioxovanadium(V) complexes consisting of imidazo[4,5-c]pyridine core in the ligand.•The newly obtained dioxovanadium(V) complexes of cyclized ligands are characterized by 1H NMR, IR and ESI-HRMS techniques.•X-ray structure of complex 1, [n-Bu4N][VO2(L1)] containing the cyclized ligand is reported here. New vanadium mediated in situ cyclization and subsequent aerobic dehydrogenative aromatization of two (L)-histidine based ligands viz. salicylidene-L-histidine and 5-bromosalicylidene-L-histidine have been reported here. Oxidative cyclization resulted from the intra ligand CC bond formation between C(sp2) of (L)-histidine imidazolyl ring and the imine CH. The newly synthesized dioxovanadium(V) complexes of cyclized ligands namely [n-Bu4N][VO2(L1)], 1 (H2L1 = 4-(2-Hydroxyphenyl)-1H-imidazo[4,5-c]pyridine-6-carboxylic acid) and [n-Bu4N][VO2(L2)], 2 (H2L2 = 4-(5-Bromo-2-hydroxyphenyl)-1H-imidazo[4,5-c]pyridine-6-carboxylic acid) have been characterized by 1H NMR, ESI-HRMS and IR techniques. Further, the structure of complex [n-Bu4N][VO2(L1)], 1 has been determined unambiguously by single crystal X-ray crystallography.