Mechanistic Study On The Metal Cluster–catalyzed Amide Reduction And Alcohol Oxidation

Amide and its derivatives widely exist in natural products and synthetic drugs.Deoxygenative reduction of amides is an important reaction for the preparation of amines.However,the selective reduction of amides is challenging due to the resonance stability and low electrophilicity of the amide bonds.Selective oxidation of alcohols to corresponding aldehydes or ketones is an important functional group conversion reaction in organic synthesis.It is thus of great significance to develop efficient and highly selective alcohol oxidation reactions.A large number of transition metal catalysts have been reported to catalyze the above two vital conversion reactions.Compared with metal complex catalysts,the structural uncertainty and the changeable active sites of cluster catalyst bring great challenges to the development of cluster-catalyzed reaction and the mechanistic investigation.In this dissertation,the detailed catalyst activation process and reaction mechanisms of deoxygenative reduction of amides with pinacolborane（HBpin）catalyzed by Y[N（TMS）₂]₃,La[N（TMS）₂]₃ complexes and La₄（O）acac₁₀ cluster are investigated by density functional theory calculations.The calculated results confirm that the M（III）-hemiaminal complex is the active catalysts for both the complexes and cluster.During catalyst activation of Y and La complexes,the polarity of H-B bond leads to the formation of an instantaneous M（III）-hydride intermediate,which is converted into an on-cycle M（III）-hemiaminal complex via facile migratory insertion.However,this kind of La（III）-hydride species cannot be formed for the La cluster.Starting from the M（III）-hemiaminal complex,the reaction proceeds via the ligand-centered hydride transfer mechanism that involves B-O bond formation,hydride transfer to B,C-O cleavage within the hemiaminal borane,hydride transfer to C,andσ-bond metathesis.The additional HBpin molecule is vital for the first hydride transfer that leads to the formation of[H₂Bpin]^-species.Our calculations reveal several important cooperative effects of the HBpin component during the hydride transfer processes.The improved mechanistic insights will be helpful for further development of selective C=O reduction.The oxidation mechanism of 4-methoxybenzyl alcohol catalyzed by vanadium catalyst on transition metal based metal-organic frameworks and the effect of electronic structure properties of metal nodes on catalytic activity were investigated by density functional theory calculations.The“cluster model”was used to build the Zr₆ metal node and the supported VO_x catalyst structure.Based on the“Zr-cluster model”,it is proved that the catalytic reaction process mainly occurs through the hydrogen transfer mechanism,including the hydrogen transfer of the alcoholic hydroxyl group to V–OH to form H₂O,the base-assisted hydrogen transfer,and O₂-involved oxidation process to complete catalyst regeneration.The detail reaction potential energy surface of the hydrogen transfer step is calculated,and results show that the hydrogen transfer assisted by NEt₃ is more kinetically favorable.The subsequent catalytic cycle requires the oxidation process involving O₂,and the whole catalytic cycle is completed with the formation of H₂O₂.However,the substrate-involved catalyst regeneration pathway is kinetically unfavorable.Based on the abovementioned results,the influence of electronic structure properties of different metal nodes on the catalytic activity of vanadium catalyst was preliminarily explored.The above insights into the dehydrogenation mechanism based on the“cluster model”have a certain guiding role when designing catalyst supports.