The Design,Synthesis And Application Of Multi-Functional Ionic Liquid System In Palladium Catalyzed Heck Reaction

The palladium catalyzed Heck Reaction plays an important role in synthetic organic chemistry, and is one of the most powerful methods in the syntheses of the fine chemicals and pharmaceuticals. The reaction requires the participation of ligand (which is crucial to the catalyst activity and stability), base (the drive of the reaction), and solvent (which is used to offer a liquid reaction phase) simultaneously. Usually, phosphines such as PPh3 are used as ligand, organic/inorganic bases as scavengers, and the volatile organic compounds as solvents. In the conventional method, the selection of ligand, base and solvent for Heck reaction is unrelated to each other although the mutual influences and limitations among the Pd precursor, ligand, base and solvent are finally showing the integrative effects on the catalytic performance and the resultant work-up. In this work we wish to employ the ionic liquid (IL) as the carrier of the functional groups of phosphine and base respectively, meaning that the originally unrelated phosphine ligand and the base got allied by IL with the similar imidazolium skeleton. This built-up multi-functionalized ionic liquid exerts the functions of ligand, base and reaction medium as one entity with the advantages of the facilitated separation, the recycling uses of the whole IL catalytic system even including the base, and the absence of organic solvents.The work carried out in this thesis was summarized as the following two parts.1. Synthesis and characterization of the functionalized ionic liquids.Three kinds of phosphine-functionlized ILs and more then ten kinds of basic ILs based on imidazolium structure were designed and synthesized successfully, which were completely characterized with the methods including ¹H NMR, ¹³C NMR, ³¹P NMR, IR, TDG, melting point detection and ESI-MS.2. The investigations of Heck reaction catalyzed by Pd complexes in the mutil-fuctionalized IL systems, which were composed of phosphine-functionlized ILs and basic IL through the mechanically combinatorial method, were carried out.In this part the catalytic performance of Pd catalysts immobilized in the multi-functionalized ILs were studied for Heck coupling reaction of PhBr (or PhI) and ethyl acrylate. After screening a series of multi-functionalized ILs, the following three systems were the optimal ones in terms of activities, stability and the recycling uses.In system 1, the conversion of PhBr and the selectivity to cinnamate acrylate were 56% and 97% respectively under the optimal conditions (140℃, reaction time 3h, catalyst concentration 1%). It's found that there were no loss of catalytic activity, no precipitation of palladium black, no accumulation of solid salt in IL solution even after 9 times recycling uses and the IL layer was as clear as the fresh one. The organic products/substrates could be extracted out easily.In systems 2 and 3, the basic ionic liquid [EPMIM]PF6 was used as scavenger to react with HI to form [EPMIM·HI]PF6 salt which could be neutralized by NaOH solution to release [EPMIM]PF₆ for next reuse. And the phosphine ligand and palladium catalyst could be recycled along with [EPMIM]PF6. The system 2 could be reused for 8 times (The system 3 could be reused for 6 times) with no precipitation of palladium black and excellent selectivity to cinnamate acrylate when it was used to catalyze the Heck reaction of PhI and ethyl acrylate.The generality of three IL catalytic systems for Heck reaction also gave the pleasing results.The application of the functional IL systems in Pd catalyzed Heck reaction can resolve a series of problems encountered in traditional systems. In aspect of the bases, the use of basic ILs overcomes the drawbacks of traditional organic/inorganic bases such as the formation of slurry mixture and un-recyclability. In aspect of the ligands, comparing to the conventional PPh₃, the phosphine-functionalized IL of [BMIM]TPPMS and [BDDMIM]PF₆ have improved oxidation tolerance, giving rise to the stability of Pd catalyst. In aspect of the solvents, the IL could lock the Pdcatalyst, phosphine ligand and base with similar IL in the whole IL phase without leaching into organic phase during the extraction (with diethyl ether or cyclohexane).It was considered that the synergic effect between the phosphine-functionalized IL and the basic IL is the dominant cause which made multi- functional IL catalytic system superior to the traditional organic system in terms of catalytic activity and stability. On the other hand, the hydrogen bond effect and the electrostatic effect between anions/cations that exist universally in the functional IL system may also contribute to the activity and the stability of the palladium catalyst for Heck reaction.