DFT Study On The Mechanisms Of Cyclization Catalyzed By Transition Metal Complexes

In this dissertation, the mechanisms of cyclization catalyzed by transition metalcomplexes are studied by using density functional theory. The investigations includetwo typical systems which were experimentally described recently: the synthesismechanism of highly substituted furans via AuCl3-catalyzed alkynyl carbonylcompounds, the synthesis mechanism of poly-substituted pyrroles viaPlatinum-Catalyzed alkynyl nitrogen compounds. We hope to comprehensivelyunderstand the metal-catalyzed unusual cyclization mechanism, explore the essentialof the metal catalysis and the solvation effects on the total reaction, and reveal therelationship between the reactivity and the structure of the substrates. The mainresearched content and results are listed following.In chapter1, we introduce briefly the study status of highly substituted furanreactions from Transition Metal-Catalyzed alkynyl carbonyl Compounds, and thestudy status of poly-substituted pyrroles reactions from Transition Metal-Catalyzedalkynyl nitrogen Compounds.In chapter2, the computational methods of density functional theory (DFT), thepolarizable continuum method (PCM) of self-consistent reaction field (SCRF), atomsin molecules (AIM) theory and natural bond orbital (NBO) theory are introducedbriefly.In chapter3, by using the density functional theory (DFT), the synthesismechanism of3(2H)-furan via AuCl3-catalyzed2-hydroxy-2-(ethynyl)cyclohexanonewas studied. The results suggest that the overall reaction of the most favorablechannel includes the following five steps: the activation of the ethynyl, thenucleophilic cyclization reaction between the carbonyl-oxygen and the ethynyl-carbon,the formation of the spiro-carbon, intermolecular hydrogen transfer, and the regeneration of the catalyst. The catalysis key of AuCl3is that its coordination withthe ethynyl decreases the anti-bonding orbital energy of the π*(C1C2), decreases theorbital energy-gap between π*(C1C2)and2p-(LP)C=O, promotes the electron transferfrom LP-(2p)C=Oorbital to π*(C1C2)orbital, and decreases the forward reaction energybarrier of the nucleophilic cyclization between the carbonyl-oxygen and theethynyl-carbon. Moreover, this study indicates that while the phenyl group connectedthe ethynyl is replaced by hydrogen, the forward reaction energy barrier of-therate-controlling step increases and the overall reactivity decreases.In chapter4, the synthesis mechanism of Substitued Tetrahydrocyclopentapyrroles via Platinum-Catalyzed Cycloisomerization of2-Alkynyl-1-azaspirohexaneswas studied. The results suggest that the most favorable channel includes thefollowing five steps: the activation of the alkynyl, the nucleophilic cyclizationreaction between the aziridine-nitrogen and the alkynyl-carbon, thecycloisomerization of cyclobutane, intramolecular hydrogen transfer, and theregeneration of the catalyst. The catalysis key of PtCl2is that its coordination with thealkynyl decreases the anti-bonding orbital energy of the π*(C1C2), decreases the orbitalenergy-gap between π*(C1C2)and2p-(LP)C N, promotes the electron transfer fromLP-(2p)C Norbital to π*(C1C2)orbital, and decreases the forward reaction energybarrier of the nucleophilic cyclization between the aziridine-nitrogen and thealkynyl-carbon.