Study On The Catalytic Performance Of Palladium Complexes With Nitrogen-Based Ligands And Supported Catalysts In The Carbonylation

Transition metal catalyst has been widely used in organic synthesis and polymers synthesis, in which palladium catalysts as its excellent catalytic performance gain a unique status. However, too much toxic organic phosphorus ligands, large dosages of catalysts and harsh reaction conditions were involved in the traditional carbonylation reactions. Nitrogen-containing ligands used in transition metal catalysis have occupied the very important positions in the replacement of phosphorus ligands. In recent years, much research results have shown that the palladium complex catalysts with nitrogen-based ligands also had excellent catalytic activity and selectivity in carbonylation reactions, which have become one of the current research highlights in the metal organic chemistry.The general difficulty in using currently known heterogeneous Pd catalysts arises from the unique reaction mechanism involving a Pd0state. Numerous reported works have shown that the catalytic active state in aminocarbonylation reactions is a Pd0species. In cases where PdⅡ was used, in situ reduction of catalytic precursor to Pd0is known to occur during the reaction, and this reduced Pd0species most likely leaches into the reaction media. Furthermore, the reversible dissolution and re-deposition of Pd0can result in the agglomeration of Pd0species into large Pd nanoparticles (Pd black), which can cause a loss of metal dispersion and surface area of the catalyst. There are a lot of methods for heterogenization of homogeneous catalysts, such as adsorption, grafting method, embedding, and so on, but these methods exist obvious problems. Such as the heterogeneous catalysts prepared by adsorption method, the combinations between homogeneous catalysts with carriers are not enough strong which lead to the leaching of active catalysts into solution during the reactions. In addition, although the combinations of metal complexes with carriers are firm for the heterogeneous catalysts prepared by grafting method, the active catalyst molecular are greatly bound at the same time, reducing the catalytic activity. Thus, in the terms of both academia and industry, developing new strategies to protect Pd0in order to achieve high activity and reusability is imperative and merits further study.In this dissertation, we will deeply discuss the application of palladium complexes catalysts with nitrogen-containing ligands and their supported catalysts in carbonylation. First, an efficient process for the synthesis of N,N-dimethylacetamide via palladium-catalyzed carbonylation of trimethylamine was investigated. The influence of reaction parameters on activity was investigated. We also studied in detail the halide promoter’s role in the reaction and found that Me+NI played two kinds of role. First, the introduced Me4NI strongly interacts with Pd nanoparticles through the formation of a double electric layer to prevent Pd black precipitation at high reaction temperatures. On the other hand, Me4NI may provide Mel in a decomposition reaction. The formation of acetyl iodide by carbonylaiton of Mel favors the cleaving efficiency of the inert unstrained C(sp3)-N bond of trimethylamine. The method provided a new possible way for activation of inert C(sp3)-N bonds, and developed an alternative for synthesis of amide compounds by carbonylation of tertiary amines.According to the idea of improving the activity and stability of palladium catalysts, a zeolite-Y confined Pd complex with nitrogen-containing ligand catalyst, PdCl2(phen)@Y, has been successfully prepared by a "flexible ligand" method. The structure and composition of the heterogeneous catalyst have been characterized by varioius physic-chemical technologies. The aminocarbonylations of aryl iodides were studied as the model reactions to test the activity of the prepared heterogeneous catalyst. It was found that complete conversions of aryl iodides and good to excellent yields (71-97%) of various amides were obtained at low Pd loadings. The turnover frequency (TOF) could be up to139h-1. A satisfactory yield was obtained even after the catalyst was reused16times and the total turnover number (TON) for the16cycles was up to2250. As evidenced by the data of AAS, UV-vis spectroscopy and XPS analysis, the palladium complex could well nestle down in the supercages of the zeolite without leaching out of the supercages during the recycling process. The significantly enhanced recyclability could be attributed to this physic-chemical double-protection strategy provided by the ligand and the zeolite structure for Pd0species generated in situ within supercages preventing the migration and leaching of palladium.In order to extend the application of the active Pd heterogeneous catalyst, we explored the alkoxycarbonylation and phenoxycarbonylation reactions of aryl iodides for synthesis of benzoates catalyzed by PdCl2(phen)@Y. Moderate to excellent yields (40-99%) of various benzoates were obtained via alkoxycarbonylation or phenoxycarbonylation reactions of aryl iodides with primary and secondary alcohols or phenols. Furthermore, its catalytic recyclability was highlighted by a comparison with that of the other two catalysts prepared by impregnation on the zeolite or graft polymer method under the same reaction conditions. The good recyclability may be attributed to the spatial restriction of the isolated nanocages and the smaller pore entrances of Y zeolite towards palladium preventing the catalyst inactivation.