Synthesis,Characterization And Catalytic Performance Of 3,5-di-tert-butylsalicylaldimine Ruthenium Carbonyl Complexes In Alcohol Oxidation

Salicylaldimine ligands have good coordination ability,can coordinate with many different metals,and the structure of these compounds is easy to modify.The electronic and steric effects of the complexes can be controlled by introducing different types of substituents.Among many metal types,ruthenium compounds show good catalytic activity in catalyzing various important chemical reactions due to their excellent redox ability.Based on this,a series of salicylaldimine ligands were synthesized in this paper,which were further reacted with Ru₃?CO?₁₂ and RuHCl?CO??PPh₃?₃ to obtain ruthenium carbonyl complexes,and the synthesized ruthenium complexes were used as catalysts to investigate the catalytic activity for alcohol oxidation reactions.This paper includes the following four parts:1.Six salicylaldimine ligands with different substituents were reacted with Ru₃?CO?₁₂ in xylene solvent to obtain six bis-ligand mononuclear ruthenium carbonyl complexes[RN=CH?3,5-^tBu₂C₆H₂O?]₂Ru?CO?₂[R=C₆H₅?1a?;4-CH₃C₆H₄?1b?;4-OCH₃C₆H₄?1c?;4-ClC₆H₄?1d?;4-BrC₆H₄?1e?;4-CF₃C₆H₄?1f?],and six mononuclear ruthenium carbonyl complexes with one of the imine bonds reduced{[RN=CH?3,5-^tBu₂C₆H₂O?]-[RNH-CH₂?3,5-^tBu₂C₆H₂O?]}Ru?CO?₂[R=C₆H₅?2a?;4-CH₃C₆H₄?2b?;4-OCH₃C₆H₄?2c?;4-ClC₆H₄?2d?;4-BrC₆H₄?2e?;4-CF₃C₆H₄?2f?].All the ruthenium complexes were fully characterized by IR,NMR and elemental analysis,and the structures of nine complexes 1a-1f,2b,2d and 2f were confirmed.The 1a-1f complexes contain two molecules of the same ligand.The O and Ru atoms in the ligand are connected by a covalent bond.The N atom in the C=N functional group of each imine is coordinated with the Ru atom,thereby forming two stable six-membered ring structures.In contrast,the C=N double bond of one of the ligands in the 2a-2f complexes is reduced to a single bond.2.Complexes 1a-1f and 2a-2f were found to be highly effective for the oxidation of both primary and secondary alcohols to their corresponding carbonyl products in the presence of NMO.The results showed that the yield of aromatic alcohol was higher than that of aliphatic alcohol.Among all the complexes,complex 1a without substituents on the benzene ring showed the highest catalytic activity.It is shown that the effect on the activity of ruthenium complex may be steric effect rather than electronic effect.3.Salicylaldimine ligands were reacted with RuHCl?CO??PPh₃?₃ to obtain five mononuclear ruthenium carbonyl complexes[RuH?L??CO??PPh₃?₂][L=3,5-^tBu₂-2-OC₆H₂-C?H?=NR][R=C₆H₅?3a?;4-CH₃C₆H₄?3b?;4-OCH₃C₆H₄?3c?;4-ClC₆H₄?3d?;4-BrC₆H₄?3e?].The products were characterized by IR,¹H NMR,³¹P NMR and elemental analysis.The structures of complexes 3a?3b?3d and 3e were confrmed by single-crystal X-ray diffraction.4.The catalytic effect of complexes 3a-3e were studied for the dehydrogenation of secondary alcohols in the presence of t-BuOK in refluxing toluene.The results show that:the catalytic activity sequence is 3d?R=4-ClC₆H₄?>3e?R=4-BrC₆H₄?>3a?R=C₆H₅?>3b?R=4-CH₃C₆H₄?>3c?R=4-OCH₃C₆H₄?.The electronic effect of the substituents in the ligand has a certain effect on the catalytic activity.