A Computational Investigation On The Arene Alkylation Catalyzed By Beta Zeolites And Ru(?) Complexes

Formation of bonding among carbon atoms is the core technology for synthesis of high value-added organic compounds. Alkylation of arene is a typical reaction of this kind. As the conventional catalysts for arene alkylation, zeolites have been widely used in chemical plants for their well-defined microchannels and tunable acidity. Transition metal complexes, especially Ru(?) complex, have drawn considerable attention for their high conversion and superior selectivity to straight chain alkylation products. In this work, with the help of extensive density functional theory based calculations, we systematically investigated the mechanisms of alkylation of arene and their derivatives catalyzed by Beta zeolite and Ru(II) complexes, and discussed the key factors that may influence the catalytic performance. The main contents of this thesis are as the follows:Firstly, combining molecular force fields and density functional theory based calculations, we investigated the reaction mechanism of Beta zeolite catalyzed tert-butylation of phenol. The results shows that this reaction is a typical Friedel-Crafts reaction and takes place via stepwise mechanism. The reaction initiates with the adsorption and dehydration of tert-butyl alcohol at the Bronsted acid site in Beta zeolite. Then, the formed tert-butyl carbenium ion reactions with the 2-or 4-position of phenol inside the microchannel of zeolite and generates alkylation products, including 2-tert-butylphenol,4-tert-butylphenol and etc. 4-tert-butylphenol is the main product as the barriers for its formation is lower. We also investigated the influence of Bronsted acidity of zeolite on the reaction mechanism and found that the change of acidity may not significantly impact the reaction mechanism and the product selectivity. There is a positive correlation between the acidity of zeoites with the reaction rates, showing that, apart from the impact of channel structure of zeolites and other secondary reactions, increase the acidity of zeolites may promote the alkylation reaction.Then, we investigated the mechanism of ethylene hydroarylation with benzene over TpRu(CO)(NCMe)Ph (Tp= hydridotris(pyrazolyl)borate) by density functional theory based calculations at B3LYP/LANL2DZ level. The primary reactions on the desired reaction path are the coordination of ethylene with Ru(?) center, the insertion of ethylene into the Ru-Ph bond, the activation of aromatic C-H and the release of ethylated benzene. The insertion of ethylene into the Ru-Ph bond is the rate-limiting step and the reaction barrier is 20.04 kcal/mol. We changed the Tp ligand of the complex to adjust the electronic structure of the Ru(11) complexes, and found that with the decreasing electron density on the Ru(?) center, the insertion of ethylene become easier, but the C-H activation goes harder. As the Tp(NO2) complex can well balance ethylene insertion and C-H activation, it would be a potential efficient catalyst for ethylene hydroarylation.Finally, we studied the electronic structure of 1,2,4-tripheny1-1,3-cyclo-pentadiene derivatives and their corresponding carbenium ions. We found that, the introduction of functional groups onto the 3 benzene rings may not impact the cyclopentadiene backbone significantly, but has strong impact on the structures of corresponding carbenium ions. The introduction of electron donation groups and those function groups that can extend the conjugation with the carbenium may benefit the charge delocalization and stabilize the carbenium ion, while the electron withdrawing groups promote the charge localization. The existence of anions breaks the conjugation and changes the charge dispersion inside the carbenium ion. Comparing with the large ClO4- and CH3SO3-, the charge localization effect of Cl- is more significant, and strongly alters the structures of the carbenium ion. According to the results from flexible potential energy surface mapping and Mulliken population analysis, the transition of cyclopentadiene carbenium ions between 3 different resonant states was determined.