Study On The Construction And Mechanism Of The Adjustable Metallocene Lewis Acid System

To develop potent and unquenchable cooperative two-catalyst systems as well as enhancement of catalytic activity by tailoring any component is an important and largely unresolved problem in cooperative catalyst field.Inspired by our previous work,the coordination of Bronsted acids to inert metallocene catalysts establishes the air and water stable metallocene Lewis acid catalytic system via the binary-acid cooperative strategy,which is applied to C-C bond and C-N bond formation reactions.Nevertheless,the systematic investigation on cooperative mechanism of metallocene Lewis acid acidity via Bronsted acids is still in vacancy.The whole thesis demonstrates the generation of metallocene Lewis acid system and their tunable mechanism.In order to construct a complete binary catalytic system and explore the real catalytic species for providing theory basis of binary acid catalytic system,Bronsted acid assisted Cp2TiCl2 cooperative process and its catalytic properties in model reactions are involved in this thesis.The brief thoughts of contents as follows:(1)By methods of NMR titration,mass spectra and theoretical computation,we analysis the coordination process of salicylic acid as well as its derivatives(Bronsted acids)and Cp2TiC12(Lewis acid).As a result,titanocene moiety attacked by substituted salicylic acids ligands displays K1O,k2O,Cl,K2O,O'coordination modes.1H NMR spectra of the coordination process of various substituted salicylic acids to Cp2TiCl2 provides an evidence that electronic effect and steric effect can bring changes bear on such complexes,for instance,when the electron-donating group act as substituent of Bronsted acid,the complex shows stronger acidity compared to electron-withdrawing group.For sake of investigating the activity of this binary acid complex,its mass spectra is analysed,and it shows the titanium-centered coordination changes arising from the dynamic interconversion of their multi stable states led to the formation of strong titanocene cation complex.In this process,16e complex is transferred to electrically deficient 14e complex,leading to the high activated catalytic species.Furthermore,the combined inert Cp2TiCl2 with 5-methoxysaliylic acid displays high catalytic reactivity in three-component aza-Diels-Alder reactions shows 86%yield and 74%endo-isomer selectivity which consistent with spectrum analysis.The whole study content not only furnished titanocene binary acid catalytic system,but provided a reference of binary acid catalytical system designing.(2)We investigate the solvent effect as regulable method to metallocene Lewis acids.We are trying to obtain the solvent regulation rules by evaluating the 14 solvents which bear different polarity in aza-Diels-Alder reaction.It turns out that protic solvents can accelerate the aza-Diels-Alder reaction,meanwhile,the production exo isomers selectivity in aza-Diels-Alder reaction 86%,when high polar methanol as solvent.While solvents fall into the nonpolar aprotic class,the reaction results show higher endo-selectivity holistically.In addition,theory computation by Gaussian 09 provides same results as above.