Theoretical Studies On The1-Decene Polymerization And The Functionalization Of Pyridine Mediated By Metallocene Complexes

Metallocene complexes, which showed high activity and selectivity in numerous chemical reactions, have attracted more and more interests in the (co)polymerization of olefin and the synthesis of functional compounds. The mechanisms of chemical reactions involved by metallocene compounds are usually sophisticated. And, the real active species and key intermediates are hard to be detected and separated just through the current experimental method. Quantum chemistry computation as a powerful tool was applied successfully to investigate the reaction mechanisms and to locate key geometric structures. And it provided valuable information for the design of new catalysts and new reactions. The mechanisms of1-decene polymerization by metallocene complexes and the pyridine functionalization were investigated by DFT calculation. The main results in this study were summarized as follows:1. Group4metallocene complexes showed unique properties in olefin polymerization and copolymerization, and the geometric regulation of metallocene complexes can produce polymers with different microstructures and different performances. In this part, we design19different metallocene compounds for1-decene polymerization based on the molecular structure of bridging and non-bridging metallocene compounds. The polymerization degree (DP) of poly(l-decene) can be improved by introducing a n-butyl substituent to Cp*of Cp2ZrCH3+and alkyl bridging groups to Ind2ZrCH3+, and the DP also can be adjusted by modifying the length of the bridging groups. Two processes of chain termination, viz. P-hydride elimination and C-H activation have been modeled.β-hydride elimination was found to be more kinetically and thermodynamically favorable fashion of chain termination in1-decene polymerization, and which is different from that of ethylene polymerization. In addition, chain initiation was confirmed to be the rate-controlling step, and in this stage, the activity is proportional to the strength of agostic interaction in the active species.2. The mechanism on the functionalization of pyridine using Scandium alkyl complexes supported by ferrocene diamide ligand was studied. In this part, we found computationally that the reaction would stop in coordinated complex of pyridine with one ethylene insertion product, which was ascribed to the difficulty of ethylene coordination with metal center and the high energy barrier of catalytic cycle. The whole catalytic cycle was accompanied by the exchange of charge between metal Sc and two amino groups. The easier coordination of pyridine with larger metal Y and Lu decreased the energy barrier and realized the catalytic cycle. The change of volume or charge characteristic of the amino group can affect the reaction. Enlarge the amino group made the pyridine coordination more difficult, and further increase reaction energy barrier. The introduction of a-CF3substituent to the amino group made the scandium more positive and the pyridine coordination became easier. The coordination of larger phenylpyridine to ethylene insertion product would deform the whole molecule to generate a counter-acting force. This force pushed the pyridine close to the methyl, reduced the energy barrier, and made the activation of C-H bond accessible. When picoline reacts with the ethylene insertion product, the second ethylene insertion with low energy barrier became possible because of the easier coordination of ethylene.