Theoretical And Experimental Study On Homogeneous And Heterogeneous Catalysis Mechanisms

Since2000, asymmetric organocatalysis has been developed as a valuable strategy for the diverse synthesis of chiral compounds. Discovery, design, application, and mechanistic investigation on new activation modes (such as enamine, hydrogen-bonding and SOMO catalysis) have dramatically advanced the development in this field. As a new type of crystalline porous material, covalent organic frameworks (COFs) are ingeniously constructed with organic moieties linked by strong covalent bonds. The well-defined crystalline porous structures together with tailored functionalities have offered the COFs materials superior potential in diverse applications, such as gas storage, adsorption, optoelectricity, and catalysis. However, catalysis applications of COFs have been seldom reported, and the first catalysis application is that taking advantage of the crystalline organic porous, COF-LZU1binds guest catalyst Pd(OAc)2via host-guest chemistry interaction to catalyze Suzuki-Miyaura reaction. Therefore, in-depth studies on the activation mechanisms of organocatalysts and the host-guest interaction mechanisms of heterogeneous COF-LZU1catalyst are of great importance for rational development of highly efficient catalytic systems. In this thesis, we have conducted both experimental and computational investigations on the organocatalysis reaction mechanisms and host-guest chemistry of heterogeneous catalyst Pd/COF-LZU1, and the main research contents include the following three parts:1. we conduct study on the direct asymmetric vinylogous Michael reaction of α,β-unsaturated y-butyrolactam (Nu) and chalcone (EI) catalyzed by the bifunctional cinchona alkaloid thiourea organocatalyst (Cat). And the results indicate that the two active sites (the thiourea group and quinuclidine amine moiety) and chiral scaffold of the catalyst Cat form an active chiral pocket, which is ideal for the dual activation of the two substrates, and the perfect control of the reaction stereoselectivity. In the catalyst-substrate complexes, the interaction of Cat with Nu is stronger than that with El, and therefore Cat preferentially activates substrate Nu. This reaction is all first-order in Nu, EI and Cat, and the rate-determining step is the C-C bond formation, which also controls the reaction stereoselectivity. Further studies on the formation mechanisms of the four stereoisomeric products reveal the origin of high reaction enantio-and diastereoselectivity. Most importantly, a new dual activation mechanism (Pathway C) was found, in which one N-HA of the thiourea moiety and the N-H of the protonated amine in Cat simultaneously activate the nucleophilic substrate Nu, while the other N-HB of the thiourea moiety activates the electrophilic substrate El.2. We further study the dual activation mechanisms on other three bifunctional thiourea-tertiary amine organocatalysts, and found that there are two dual activation mechanism, i.e. Pathway B and Pathway C, in the bifunctional thiourea-tertiary amine organocatalysis. In the Pathway B mechanism, the two N-H (N-HA and N-HB) of thiourea moiety in the catalyst simultaneously activate the nucleophilic substrate, while the N-H of protonated amine in the catalyst activates the electrophilic substrate. And in the Pathway C mechanism, one N-H (N-HA) of the thiourea moiety and the N-H of the protonated amine simultaneously activate the nucleophilic substrate, while the other N-H (N-HB) of the thiourea moiety activates the electrophilic substrate. this study results show that via which dual activation mechanism a reaction proceeds, depends on the matching situation of the two substrates, not on the catalyst structure. Finally, according to the law of the summary, we predict the dual activation mechanisms of three reactions catalyzed by bifunctional cinchona alkaloid squaramide organocatalysts:one is Pathway B mechanism, and the other two is Pathway C mechanism.3. We finally study on the host-guest chemistry of COF-LZU1(host) with Pd(OAc)2(guest) within the catalyst Pd/COF-LZU1. And the results indicate that the host-guest chemistry could occur on the surface and in the channel, not in the interlayer of COF-LZU1. There are ten kinds of binding sites possibly having host-guest interaction with Pd(OAc)2on the surface and in the channel, and we detailly investigated the host-guest interaction of each binding site with Pd(OAc)2. The results reveal that the binding abilities of channel sites with Pd(OAc)2are stronger than that of surface sites with Pd(OAc)2. The specific binding site of Pd(OAc)2is the imine site in the channel of COF-LZU1.