Theoretical Study On Mechanism Of Transition-Metal-Catalyzed Hydrocarbonation Of Alkenes And Oxidation

Transition metal catalysis lies at the heart of modern chemistry, providing tremendous tools for the production of materials, drugs, agricultural chemicals, fuels and so on. Hydrocarbonation of alkenes is a high atom-economic method of C-C bond formation, allowing the access to substituted alkanes. Transition-metal-catalyzed oxidation introduces oxygen-containing functionalization groups into substrates or increases the degree of unsaturation through dehydrogenative processes. Meanwhile, oxidative bond cleavages are also applied to the depolymerization of natural polymers, e.g. lignin. The development of chemistry tightly connects with reaction mechanisms. The dominant pathway and the factors controlling rate and selectivity are both appealing issues. Theoretical calculations based on quantum-chemical principle have been proved to be intuitive and convenient alternatives for mechanistic investigation. With the aid of theoretical methods, the mechanisms of several transition-metal-catalyzed hydrocarbonation of alkene and oxidation reactions have been studied in this dissertation.The first part of this dissertation reviews the advance of transition-metal-catalyzed hydrocarbonation of alkenes, including hydroalkynylation, hydroarylation, hydrovinylation, hydroalkylation, hydroacylation, hydroesterification, hydroimination and hydroaminocarbonylation. The concerned transition-metal-catalyzed oxidation reactions including Wacker-type oxidation, catalytic bond cleavages of lignin model compounds and the dehydrogenation of methanol are also reviewed. Furthermore, the employed density function theory (DFT) methods and basis sets are introduced.The second part conducts a DFT study on nickel-catalyzed hydroheteroarylation of alkyl- and aryl-substituted alkenes. The results support the mechanism of C-H bond oxidative addition/hydronickelation of alkene/reductive elimination, and exclude direct hydrogen transfer, single electron transfer, radical pathway and the pathway in high spin state. The secondary orbital interaction between the aromatic substitutes and the nickel center is found to be critical to the Markovnikov selectivity.The third part investigates the cobalt-catalyzed hydroacylation of 1,3-diene. The pathway involving oxidative cyclization,β-H elimination and C-H reductive eliminaton is found to be more kinetically favored over the oxidative addition of H-COR bond. The site of acylation is determinined in oxidative cyclization while the site of the double bond of products is determinined in the C-H reductive elimination. Both the electronic and steric effects of the substitutes at the C3 site of 1,3-diene influence the regioselectivity of oxidative cyclization.The fourth part turns to the mechanism of nitrite-modified Wacker-type oxidation of unbiased alkenes. The tBuOH-ligated Pd-Cu heterobimetallic compounds are found to be active catalytic species while the dominant mechanism of oxymetallation step is syn addition. The rate-and regioselectivity-determining step is the following 1,2-H shift, and the relationship between the radical character of this step and the regioselectivity is also clarified.The fifth part provides a combined theoretical and experimental study on vanadium-catalyzed selective C(sp3)-O and Ar-C(sp3) cleavage of phenolic β-O-4 lignin model compound. For the C(sp3)-O cleavage process, a new catalytic cycle of VⅤ-VⅣ-VⅢ-VⅣ-VⅤ is located while a completed pathway involving stepwise O-O/Ar-C(sp3) cleavage is located for the Ar-C(sp3) cleavage process. The bond cleavage selectivity results from the different T1 (ground triplet state)-HOMOs-separation/charge dispersion effects of ligands and the different formal oxidation states of vanadium in TOF-determining transition states. Control experiments about base and oxygen pressure give further supports for the calculation results that base is not essential for Ar-C(sp3) cleavage but promotes the dehydration of P-hydroxyl aldehyde, and the O-O bond cleavage is the rate-determining step of the Ar-C(sp3) cleavage process.The last part addresses the mechanism of the dehydrogenation of methanol by PNP-Ru complexes. A self-consistent mechanism is located, in which only basic and neutral species are involved. This mechanism highlight the catalytic role of methanol in the dehydrogenation of Ru-H intermediate and the hydride transfer of formate. It also explains the experimental observations on the intermediates and the resting states of catalysts.