Pyridine–triazole ligands for copper-catalyzed aerobic alcohol oxidation

摘要: A series of Cu(NN′)2(OTf)2 complexes containing pyridine–triazole ligands [OTf = OSO2CF3; NN′ NN′Ph (1), NN′hex (2), NN′py (3)] with different substituents at the triazole N4 position or 2,2′-bipyridine (bpy; 4) have been synthesized. Crystal structures 1 and 3 reveal a trans-isomer strong preference for regular-type coordination (for 3) whereas Cu–bipyridine complex 4 is more stable in cis-form. Cyclic voltammetry 1–4 suggest that electron-donating strength follows trend: bpy > ∼ NN′Ph. The catalyst systems consisting 5 mol% Cu(OTf)2/NN′/TEMPO (TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxy) presence 2 × 2.0 cm2 Cu0 sheets as reducing agent 10 N-methylimidazole (NMI) exhibit good activities aerobic oxidation benzyl alcohol to benzaldehyde. Catalytic studies shown were higher electron-rich N-based ligands. Furthermore, aliphatic alcohols such 1-hexanol 2-methyl-1-pentanol using Cu system ligand room temperature afforded corresponding aldehydes >99% 46% yields, respectively after 24 h.