Theoretical Investigations on Transition Metal (Nickel and Copper)-Catalyzed C-C and C-N Bond Formation Reactions

Author:Qi Zheng Hang

Supervisor:ma jing

Database:Doctor

Degree Year:2019

Download:89

Pages:132

Size:10862K

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3d transition metals,such as nickel and copper,have attracted more and more attention in the field of catalysis because they are cheap and readily available.Especially in recent years,3d transition metals have achieved great success in the reactions of carbon-carbon and carbon-nitrogen bond formation,showing greatly potential development prospects and application values.In the catalytic reactions,3d transition metals often show different performance.As a result,it is necessary to study the mechanisms of 3d transition metal-catalyzed reactions in order to get insightful information about the key intermediates and transition states such as geometrical structures,charge distributions and changes of oxidation states of metals.And then hopefully the studies could offer useful theoretical guidance for the design of new catalysts and reactions.This thesis employs density functional theory(DFT)calculations to systematically study the mechansms of nickel/photoredox-catalyzed carbon-nitrogen cross-coupling reaction and copper hydride-catalyzed conversion of carbon dioxide,elucidating that the photocatalyst plays a key role in the generation of active nickel(0)catalyst and change of oxidation state of nickel catalyst;copper hydride catalyst plays a key role in the reduction of carbon dioxide to generate the final silyl ether product.1.Theoretical investigations on nickel/photoredox-catalyzed carbon-nitrogen cross-coupling reaction.For the carbon-nitrogen cross-coupling reaction catalyzed by nickel/photoredox,our computational results show that the photocatalyst facilitates the reaction through the modulation of the oxidation state of nickel via single-electron transfer(SET).The Ni(0)catalyst initiates the C-N cross-coupling with the activation of the Ar-Br bond by an ion-pair(SNAr-like)pathway.The photocatalyst*[Ir(Ⅲ)]is engaged in the nickel catalytic cycle to oxidize the Ni(Ⅱ)complexes to facilitate the subsequent deprotonation and C-N reductive elimination.In contrast,the pathway of the Ni(Ⅰ)-initiated reaction is greatly suppressed due to the higher barrier for the oxidative addition of Ar-Br to the Ni(I)catalyst.In addition,the reduction of the experimentally used Ni(Ⅱ)salt is promoted by a photoredox-catalytic hydrogen atom transfer.Furthermore,the pathway of triplet-triplet energy transfer between the photocatalyst and the Ni(Ⅱ)complex is less likely to occur due to the mismatch in energy levels.It can be concluded that the participation of the photocatalyst*[Ir(Ⅲ)]in nickel catalysis can modulate the oxidation state of transition-metal complexes to promote the catalytic reaction.2.Theoretical investigations on copper hydride-catalyzed conversion of carbon dioxide.For the conversion of carbon dioxide catalyzed by copper hydride catalyst,our computational results show that carbon dioxide could insert into the Cu-H bond to generate the formate copper(Ⅰ)complex.Catalytic amounts of carboxylate could activate the silane,facilitating the transfer of hydride to copper atom to regenerate the copper hydride catalyst.When styrene is involved in the reaction,the insertion of styrene into the Cu-H bond would generate a chiral carbon center and the chiral center will maintain its configuration to the final product.Carbon dioxide can insert into the Cu-C bond via a four-menbered transition state and this step is rate-determining.Also,catalytic amounts of carboxylate could activate the silane,facilitating the transfer of hydride to copper atom to regenerate the copper hydride catalyst.The generated silyl carboxylate could be reduced to the aldehyde intermediate under the catalysis of copper hydride.The aldehyde intermediate can be reduced to a silyl ether compound which is the precursor of the final alcohol product through the catalysis of copper hydride catalyst.From the computational results,copper hydride catalyst experienced three catalytic cycles to convert carbon dioxide and styrene to silyl ether product.The enantio-and regio-determing steps are both the insertion of styrene into the Cu-H bond.We also compared the insertion processes of silyl formate and styrene into Cu-H bond.The barrier for the insertion of silyl formate into Cu-H bond is lower than styrene,which suppresses the insertion of styrene.As a result,it will cause no product generation.In addition,when 1,3-diene acts as a substrate,it will be transformed to an allyl copper(Ⅰ)intermediate and then react with a carbon dioxide to form a carbon-carbon bond through a six-membered transition state.