Synthesis,Structures And Reaction Of Metal Complexes Containing Nitrogen-oxygen Ligands

Metal compounds containing nitrogen-oxygen ligands exhibited special optical properties and high catalytic activities toward polymerization,hydrophosphination,Meerwein-Ponndorf-Verley(MPV)reactions by virtue of its strong metal-ligand bonds and exceptional tunable steric and electronic features.The nitrogen,oxygen-coordinated transition metal catalysts are recognized as the most efficient catalytic system for MPV reactions.With the requirements of friendly environment and industrial applications,the use of earth-abundant,inexpensive main group metals alternative to expensive noble metals in the transition metal catalytic reaction,and the development of low toxicity,low cost and efficient MPV reaction catalyst has become a hot topic for chemical workers.The purpose of this paper is that the synthesis of different structural metal compounds by the main group metal reagents reacting with the compounds of containing bidentate or bidentate nitrogen-oxygen ligands.Through tunable features of ligands to the center main group metal atoms and the synergistic effect of heterobimetal to substitute for the transition metal catalyst achieving efficient catalytic reactions.The complete characterization of the metal compounds containing nitrogen-oxygen ligands was carried out to obtain detailed structural properties.Then,they were applied to MPV catalytic reactions and mechanism studies in order to obtain efficient catalysts,and provide the experimental and theoretical support for the further study of heterobimetallic catalytic reaction mechanism.The main research contents are described as follows.1.Treatment of bidentate N,O-ligands(2-1~2-4)with AlMe3 or the magnesium reagents(nBu2Mg,MgBr2 or MeMgBr),six novel aluminum compounds(2a~2f),seven bidentate N,O-magnesium compounds(2g,2i,2j,2k,2m,2n,2o)and two lithium-containing intermediate compounds(2h,2l)were obtained in good yield.Compounds 2a~2o were characterized by 1H and 13 C NMR spectroscopy,elemental analyses and single crystal X-ray diffraction techniques.Bidentate N,O-aluminum compounds 2a~2d were used to catalyze the MPV reaction of aldehydes and ketones to produce primary or secondary alcohols,which showed high catalytic activity and selectivity.Compound 2a as catalyst at 5 mol % loading and under solvent-free in 15 min exhibited the highest activity and the best catalytic effect in the MPV reaction of benzaldehyde.At the same time,different types of carbonyl compounds were efficiently and highly selectively reduced to the corresponding alcohols without side reaction of Tishchenko or aldol.Bidentate N,O-magnesium compounds 2i,2j,2m and 2n were used to catalyze the MPV reaction of ketones to synthesize secondary alcohols.The compound 2n of the seven-membered ring structure at 5 mol % loading and KOH as the base exhibits the best catalytic activity and has a higher yield for aromatic and aliphatic ketones.In addition,we speculate on the possible mechanisms of bidentate N,O-aluminum and magnesium compounds in catalyzing MPV reactions,respectively.2.We provided a simple method for synthesis of novel N,N,O-tridentate ligand compounds by selectively activating the C-H bonds of methyl groups of TMEDA with nBu Li.The specific reaction process of this method is: in the presence of N,N-dimethylaniline,TMEDA is followed by lithiation,carbonyl addition and hydrolysis to obtain the corresponding N,N,O-tridentate ligand compounds.Although it is reported that TMEDA plays a role in coordination and depolymerization of n-BuLi is usually not lithiated,this method not only lithates the C-H bond of TMEDA methyl group,but also has the advantages of high selectivity,mild reaction conditions and short time.At the same time,the applied range of TMEDA has been further enhanced in synthetic chemistry.3.Three N,N,O-tridentate ligand compounds,HOC(CH2)5CH2N(Me)CH2CH2NMe2(3-1),HOC(CH3)(Ph)CH2N(Me)CH2CH2NMe2(3-2)and HOC(CH2)4CH2N(Me)CH2CH2-NMe2(3-3),were synthesized and characterized by 1H and 13 C NMR spectroscopy,elemental analyses techniques.The bromate of compound 3-1 was cultured to obtain a single crystal structure of 3a.In addition,eight N,N,O-tridentate metal compounds were obtained by reacting with 3-1 and different metal reagents,three homonuclear magnesium compounds(3b~3d)and five lithium-containing heterobimetallic compounds,Which comprises two Mg-Li compounds(3e,3f)and three Al-Li compounds(3g~3i).The structures of 3a~3i were characterized by elemental analysis,1H,13 C,7Li,27 Al NMR and single crystal X-ray diffraction techniques.And the synthetic process and structural characteristics of heterobimetallic compounds 3e~3i were further discussed.Each of the compounds 3b~3d was tested for the capability of catalyzing MPV reactions.3e exhibited showed the best catalytic activities,which is obviously higher than the corresponding mononuclear metal precursor 3d.It would be due to the synergistic effect of magnesium and lithium for 3e,which added the Lewis acidity and the electrophilicity of metal center and increased the attack probability to benzaldehyde.