Studies On The Structural Properties And Catalytic Efficiency Of 8-quinolinolato Metal Complexes

8-Hydroxyquinoline and its derivatives have been used extensively as extraction, precipitation and chromogenic reagents in analytical, inorganic and organic chemistry rather than the ligands of catalysts. The probably reason is that people generally regarded the 8-quinolinolato metal complexes as stable compounds and not suitable for catalysts. In the view of structure affecting properties, several hexadentate binding 8-quinolinolato metal complexes with distorted structures were designed and used as catalysts for the oxidation of cyclohexane, hydroxylation of benzene and oxidation of alcohol with hydrogen peroxide. The results indicated that the distorted hexadentate binding 8-quinolinolato metal complexes exhibited a higher efficiency in the oxidations than that of symmetric complexes. These facts suggested that the catalytic activity of the hexadentate binding 8-quinolinolato metal complexes could be adjusted by modifying their structures. The specific works were described as follows:(1) We conveniently synthesized a series of hexadentate binding 8-quinolinolato iron(â…¢) complexes (Q₃Fe^â…¢), and investigated their catalytic performances in the oxidation of cyclohexane. The experimental results showed that the 5 and 7-di-halogenated Q₃Fe^â…¢catalysts were stable and significantly improved cyclohexane conversion provided that reaction time was prolonged. Interestingly, the 5-chlorinated and 5, 7-di-chlorinated ligands co-coordinated Fe^â…¢catalyst [(Cl₂Q)₂(ClQ)Fe^â…¢i] was superior to the single ligand coordinated Fe^â…¢ones in the reaction rate and catalytic activity, being due to it having a distorted hexadentate structure.(2) We further investigated the catalytic activities of the Q₃Fe^â…¢complexes in the hydroxylation of benzene with hydrogen peroxide. The results also showed that the 5-chlorinated and 5, 7-di-chlorinated ligands co-coordinated Fe^â…¢catalyst [(Cl₂Q)(ClQ)₂Fe^â…¢] can more efficiently catalyse the hydroxylation of benzene than the single ligand coordinated Fe^â…¢ones in water-acetonitrile medium.(3) A series of hexadentate binding 8-quinolinolato manganese(â…¢) complexes (Q₃Mn^â…¢) have been proposed and conveniently synthesized for the oxidation of alcohol with aqueous hydrogen peroxide in water-acetone media with ammonium acetate and acetic acid as additives. The good results is due to their special hexadentate binding structures that could be easily converted to the corresponding pentadentate with pendant hydroxyl groups via opening an axial Mn-O bond in the reaction media.