Tridentate Ir Complex Theory And Catalytic Properties Of Alkane Dehydrogenation

Hydrocarbons, especially saturated hydrocarbons, are the main constituents of petroleum and natural gas, the feedstocks for chemical industry. Therefore, the transformation of saturated, as well as aromatic, olefinic, and acetylenic hydrocarbon by C-H activation to much more useful alkenes, alcohols and ketones etc. constitutes an extremely important field of present chemistry. The adjustability of the steric and electronic properties of the complexed metal center of pincer complexes makes these complexes have a broad application in C-H bond activation. In decades, iridium pincer complexes (also called tridentate complexes) have been extensively studied in homogenous dehydrogenation of hydrocarbons. Exploring more effective homogenous catalysts for hydrocarbon dehydrogenation is one of the main goals of current research.In this thesis, we have completed the followings:1. Applying the Density Function Theory (B3LYP), LANL2DZ basis set for iridium, and 6-31G* for other elements other than iridium without truncation of substituents, we first studied the known catalysts with good performances to find out their common characteristics in electronic and steric properties. We then systematically investigated the electronic and steric effect of different known and unknown types and substituents of tridentate ligands on the iridium center and quantitative descriptions are obtained. These information should be also useful in evaluating the electron donating ability and steric properties of these various tridentate ligands which might be used in other research fields. Based on these calculation results, we proposed a few iridium catalysts which might be potential good alkane dehydrogenation catalysts.2. Themodynamics of related dehydrogenation reactions were studied including of temperature and solvent effects on enthalpy and Gibbs free energy changes by DFT calculations. The calculation results are consistent with reported experimental results and predict that (k3-1,3-(OPtBu2)2C6H3)Ir(H)2 (3b(H2)) should be a good catalyst for dehydrogenation of alcohol.3. We applied a known pincer catalyst 3b(H2) that has not been applied in dehydrogenation of alcohol to catalyze the transfer dehydrogenations of bentanol and 1-butanol at 200℃using TBE as the hydrogen acceptor. Both alcohols have been completedly dehydrogenated, showing 3b(H2) to be a good dehydrogenation catalyst with an efficiency no less than that of (k3-C6H3-2,6-(CH2PtBu2)2) IrH2 (2b(H2)), consistent with the theoretical calculation.