DFT Studies On The Mechanisms For Metathesis Reaction Catalyzed By The New Type Of Olefin Metathesis Catalysts

The metathesis reaction catalyzed by the new type of olefin metathesis catalystsattracted widely interest for its great application prospect in organic synthesis over thepast few years. In this thesis, the mechanism for reaction catalyzed by the new type ofolefin metathesis catalysts was carried out using density functional theory. Weproposed the optimal catalytic cycle.The detailed mechanisms of ring closing metathesis reaction (RCM) catalyzed bypyrocatechol ligand catalysts. All of the transition states and intermediates were alsoperformed with the BP86method. Vibration analysis and intrinsic reactioncoordinates (IRC) were calculated for the transition states to confirm that suchstructures indeed connect two relevant minima. The computational results give amechanism as followings. The reaction begins with the dissociation of pyridine ligandfrom Ru penta-coordinated catalyst. Subsequently,1,6–hexadiene coordinates to theRu center through the side-bound pathway, generating a metal carbene complex withtetragonal-pyramid geometry. Then, twice [2+2] addition and retro-cycloadditionreaction occur, giving the product cyclopentene. The pathway of olefin coordinates tothe Ru center through the side-bound is the optimal route.The detailed mechanisms of cross metathesis reaction (CM) catalyzed bycarbyne catalysts were studied using density functional theory (DFT). We analyzed allthe transition states and intermediates by the two-layer oniom method(M06/LANL2DZ: M06/LANL2DZ). Through our calculations, we found that crossmetathesis reaction catalyzed by carbyne catalysts is mainly divided into two parts.For the part one, iodide ions firstly add to carbon carbyne, generating the metalcarbine, and then phosphorus ligands dissociate from the metal center Ru. For the parttwo, olefin laterally coordinates to the Ru center. Subsequently,[2+2] addition andretro-cycloaddition reaction occurs, giving the product. This thesis investigates themechanisms of cross metathesis reaction (CM) catalyzed by trihexylphosphine ligandcatalysts, comparing with ones by pyridine ligand. The results have shown thatreaction route remains the same while adopting different ligands, which again provesthe rationality of our pathway.