Mechanisms And Structure Activity Relationships Of Transition Metal-Catalyzed C-O Bond Activation

Biomass conversion is highly dependent on the construction of functional groups mainly by C-O bond cleavage and reorganization,which means that the development of novel,efficient,and mild C-O bond selective conversion methods is one of the scientific problems to realize the efficient utilization of biomass.As the representative molecules of biomass materials,alcohols have the advantages of high atomic economy and easy availability,and the C-O bond selective activation conversion for alcohols also has significant theoretical and application values.As a C1 source,carbon dioxide is an attractive synthetic substrate that occupies a place in green chemistry for its abundance,non-toxicity and renewability.As more and more transition metal-catalyzed C-O bond activation strategies are developed,the associated mechanistic issues have received more and more extensive attention.The development of density functional theory(DFT)provides an intuitive and convenient approach for transition state simulation and mechanism investigation.The evolution of data science,such as linear regression and machine learning,has provided powerful tools for structure-activity relationship(SAR)analysis and prediction.In this thesis,the potential mechanisms of transition metal-catalyzed C-O bond activation and carbon dioxide conversion are systematically investigated,and the activation patterns are modeled and predicted.Chapter Ⅰ provides provides an overview of density functional theory and the details of the data analysis,as well as a brief review of representative work on the recent years of transition metal-catalyzed C-O bond activation functionalization of alcohols and their carboxylation with CO2 involving alcohols as well as derivatives.The review section of the experimental work is divided into four sections according to the type of alcohols:alkyl alcohols,allyl alcohols,propargyl alcohols,and benzyl alcohols phenols.Particular attention is given to the critical mechanisms involved in the C-O bond activation and the application of quantum chemical calculations of these reactions.Chapter Ⅱ explores the mechanistic details of the nickel-catalyzed regioselective carboxylation of allylic alcohols,proposing a novel mechanism involving the activation of allylic alcohol with CO2 and H2O.In particular,water acts as a "proton shuttle" in the hydrogen transfer process,allowing C-O bond cleavage through in situ esterification via a SN2-type coordination substitution rather than the classical direct oxidative addition.The regioselectivity of terminal carboxylation is determined by the steric effect,and the stereoselectivity is mainly controlled by the thermodynamic stability of the carboxylation precursor,and the kinetic facility of the elementary carboxylation step.This mechanism of allyl alcohol esterification activation via CO2 and H2O assistance is widely applicable to different types of allyl alcohols and is expected to be extended to more alcohol substrates.Chapter Ⅲ explores the mechanistic details of rhodium dimer-catalyzed carbon-hydrogen bond activation,chemoselectivity of carboxylation,lactonization and C-O bond activation.Among them,the base is crucial for the carbon-hydrogen bond activation and determines the activation energy barrier.In the carboxylation step,CO2 can be inserted into the Rh-O and Rh-C bond kinetically and thermodynamically,respectively.In the lactonization process,conjugate acids and CO2 played vital roles in protonation and catalyst regeneration.This chapter summarizes the linear correlation between the conjugate acid’s pKa and the activation energy barrier of a carbon-hydrogen bond with the linear regression analysis.Chapter Ⅳ has effectively combined and rationally extended the scientific issues of Chapter Ⅱ with the analytical approach of Chapter Ⅱ to provide the systematic analysis of Pd-catalyzed C-O bond activation of allylic alcohols.The study provides a data science-driven model based on multiple linear regression(MLR)analysis that unifies and correlates the activators and ligands in the reaction to achieve a reliable prediction of the C-O bond cleavage energy barrier.The model is statistically sound,provides high predictability,and gives reasonable predictions when new activators and ligands are added.These findings are instructive for the development of the related C-O bond activation reactions and are expected to help the development of more efficient activation transformations of alcohols.