No abstract

2010) On the mechanism of reduction of maleate by a Co(I) complex with a macrocylic ligand in aqueous solutionsRecently, it was shown that a Ni(I) complex with a tetraazamacrocyclic ligand (Ni I (1, 4, 8, 11-tetraazacyclotetradecane) þ , NiðIÞL þ 2 , cyclam), reduces maleate in aqueous solutions. It was decided to investigate whether this is a general reaction of low valent transition metal complexes. In this study, the reactions of Co I L þ (L ¼ 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) with maleate were investigated. The effect of the addition of maleate to aqueous solutions containing this low valent metal complex, prepared via the pulse radiolysis technique, was studied. The d ! * complexes formed between the monovalent cobalt complex and maleate were detected and characterized by UV-Vis spectroscopy. The nature of the final products formed was studied and detailed mechanisms of the reduction processes are proposed. The mechanism and kinetics of the reaction of Co(I)L þ with maleate was studied applying pulse-radiolysis and analysis of the final products.

Recently, it was shown that NiI and CoI complexes with tetraazamacrocyclic ligands [namely, trans‐III‐NiIL3+ (L3 = 1,4,8,11‐tetraazacyclotetradecane), NiIcyclam and rac‐CoIL1+ (L1 = 5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradeca‐4,11‐diene, dien)] reduce maleate ions in aqueous solutions. It was decided to expand the study to further NiILi+ complexes. In the present study, the reactions of rac‐NiIL1+ and meso‐NiIL2+ (L2 = 5,5,7,12,12,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane) with maleate ions were investigated. The effect of the addition of maleic acid to aqueous solutions containing these low‐valent metal complexes, prepared by the pulse radiolysis technique, was studied. The d→π* complexes formed between monovalent nickel complexes and maleate ions were detected and characterised by UV/Vis spectroscopy. The nature of the final products formed depends strongly on the nature of the metal and the ligand. Detailed mechanisms of the reduction processes are proposed and compared with those previously reported. The results indicate that the electronic configuration of the central cation as well as the reduction potential of the complex and steric hindrance induced by the ligand affect the reduction mechanism of maleate ions by these analogous complexes.