Investigation Of The Lewis Acidity Of Metal Complexes By Using Electrospray Ionization Mass Spectrometry

Metal complex consists of a central metal ion and a surrounding molecular or ionic ligand,which has a variety of uses in both nature and industry.On one hand,numerous studies have proved that what has an important influence on homogenous catalysis is the Lewis acidity of the central metal,and the Lewis acidity plays an active role not only in the mechanism study but also in catalyst design.However,there is not a general evaluating standard for evaluating the Lewis acidity of metal complexes.On the other hand,the interaction between metal complexes and reactants also influences the catalytic reaction process.Particularly,bimetallic complexes have multiple coordination modes with reactants,but there also lacks an effective research method.Against current difficulties in the above issues,this thesis deals with:A method is developed to measure the Lewis acidity of metal complexes by using electrospray ionization mass spectrometry(ESI-MS)is developed,in which the dissociation energy of the “metal complex-organic base Lewis pairs” is quantified.Metal complex and organic base form Lewis acid-base pair at first,then collision-induced dissociation(CID)reaction of the Lewis pairs with argon is occurred in the collision cell by gradually increasing the collision energy and the abundance of the resultant ions at different energies is obtained.In this way,the Lewis acidity of Salen-type metal complexes was compared in four areas: central metals,axial anions,ligand frameworks and substituent effects.Through the experiments,it is demonstrated that the aluminum complex is much more Lewis acidic than other metals',and the Lewis acidity of the complex with ethylenediamine skeleton are weaker than other ligand frameworks.The fluorine group on the ligand slightly increases the Lewis acidity of the metal complex,while the methoxy on the ligand significantly weakens the Lewis acidity.Besides,an on-line sampling system is designed to monitor the coordination process and coordinate competitive process of metal complex between organic bases in-situ.Based on ion mobility technology,the coordination mode of binaphthyl-type bimetallic Salen complex and biphenyl-type Salen complex with different hindered organic bases was studied respectively.Bimetal complexes have some variety coordination modes,among which the coordination mode of binaphthyl-type bimetallic Salen complex the is more complex than the biphenyl-type Salen complex on account of its wider dihedral angle.