Theoretical Calculation Of Transition Metal-catalyzed B-H Activation Of Carborane

Carborane is a general term for a class of compounds formed by replacing boron atoms of borane compounds with carbon atoms.It is a kind of polyhedral atomic clusters with three-dimensional aromatic properties.The caged three-dimensional structure of carboranes and its unique electronic properties give the hydrogen atoms in each caged structure different properties.B-H functionalization on carborane have developed rapidly in recent years,however,the selective B-H activation reaction still faces many challenges.The challenges are principally reflected in two aspects: the polarity and nucleophilicity of B-H bonds is greatly lower than that of the corresponding C-H bonds due to the electron-deficient characteristic of boron.On the other hand,boron vertices with different electron environments on carboranes make it impossible to synthesize regioselective products,which result in multiple isomers.In recent years,chemists have achieved regionally selective B-H activation on carboranes using guide groups,ligands,transition metal,and electrochemistry.In this paper,the B-H functionalization of carboranes was studied by density functional theory.The research contents as follows:1.Theoretical calculation of regioselectivity and solvation effects on B–H activation of O-carborane guided by directing group.This study focuses on uncovering the regioselectivity,directing group,ligand,and solvation effect in B–H activation,which was investigated by DFT calculations.The reaction mechanism was investigated in vacuum,and the advantageous reaction pathway and rate-determining step were determined.Furthermore,the solvation effects and the ligand that coordinated with Pd were studied.The results showed that in neutral and cationic pathways,the anion(OTf)/ligand(1,10-phenanthroline)exerted significant influence on the transition metal catalytic center Pd,thus affecting B–H activation at different sites.The solvation effects also exerted significant influence on the reaction.The greater the polarity of the solvent,the greater the influence on the energies of all stationary points.2.A Theoretical Investigation on Migration Mechanism in B-H Activation of Carboranes.Density functional theory(DFT)was used to investigate the possible migration mechanism of B-H activation on carboranes.The effect of inducing groups,mediating atoms,and ligands were clarified,and the specific reaction process and driving force of transition metal migration on carboranes were explored.The study of thermodynamics,dynamics,wave function analysis,and bond order show that hydrogen atoms and ligands have significant effects on metal migration on carboranes.The results indicated that the transition metal complexes can migrate between B/B or C/B mediated by H atom,which contributes to regioselective B-H activation on carboranes.3.A Theoretical Investigation on electron transfer mechanism in B-H Activation reaction of Carborane.The possible mechanism of electron transfer on n-carboranes was proposed and researched by DFT.The possibility of single electron transfer of n-carborane anions directly at the anode was elucidated.Thermodynamics,dynamics and charge analysis show that oxygen molecules and hydroxide ions do not directly participate in reaction process of single electron transfer.The protons in the solution may be involved in electron transfer on n-carboranes.In this paper,the cagelike three-dimensional structure and unique electronic properties of the polyhedral atomic cluster complex carborane were studied by theoretical calculation on the B-H functional group of carborane.By density functional theory(DFT)calculation,the influences of the mediating atoms,guiding groups,ligands and solvation effects on the selective B-H activation of carborane region were revealed,and the rate control steps and the dominant reaction path were determined.