Tuning the ring-chain tautomerism of a tetrahydroquinazoline/Schiff base system with unexpected methanol oxidation

The ring-chain tautomerism of a tetrahydroquinazoline/Schiff base (H2Lring/H2Lchain) system can be controlled by metal coordination through varying ligand stoichiometry of the reaction H2L + M2+ [H2Lring: 2-(3-tosyl-1,2,3,4-tetrahydroquinazolin-2-yl)quinolin-8-ol; H2Lchain: N-{2-[(8-hydroxyquinolin-2-yl)methyleneamino]benzyl}-4-methylbenzenesulphonamide and M: Co2+ and Cd2+]. The ring tautomer H2Lring undergoes a ring-opening reaction upon formation of dinuclear complexes M2(Lchain)2, while Co2+ and Cd2+ stabilise the tetrahydroquinazoline ligand in their mononuclear complexes M(HLring)2. The detection of 3-tosyl-1,2,3,4-tetrahydroquinazoline on the methanolic mother liquors of Co2(Lchain)2 revealed the acid-catalysed hydrolysis of the Schiff base ligand and the cobalt-mediated aerobic oxidation of methanol to formaldehyde.

We have demonstrated that the ring-chain tautomerism of a tetrahydroquinazoline/Schiff base (H2Lring/H2Lchain) system can be controlled by cadmium and cobalt coordination through varying ligand stoichiometry. Besides, this investigation revealed the unexpected cobalt-mediated aerobic oxidation of methanol to formaldehyde.Figure optionsDownload as PowerPoint slide