Theoretical Study Of Mechanisms Of C-H Bond Activation Of Organic Molecules With Metal Carbenes

The C-H bond activation reaction is one of the most popular research subjects in the organic field,especially for the C-H bond activation of aromatic hydrocarbons.A large number of experimental and theoretical studies have been reported the aromatic C-H bond activation catalyzed by transition metals.Among them,phenol is the simplest phenolic compound and also a synthetic raw material for many materials and useful chemicals.Since the copper catalysts were used to activate C-H bond in phenol,a series of transition metal catalysts such as palladium,iron and ruthenium have been developed by organic chemists.However,due to active groups(hydroxyl)of phenol,only the O-H bond insertion products were obtained.It is of great significance to achieve high selectivity of C-H bond functionalization of phenols.In our previous theoretical work,the mechanism of gold-catalyzed C-H insertion of phenols with diazo compounds was studied.We found that the water molecules play an important role,which was verified by controlled experiments.Based on this study,the following works are mainly carried out:1.The mechanism of O-H bond and C-H bond insertion reaction mechanism catalyzed by copper-bisoxazoline,copper-pyridine bisoxazoline and dirhodium tetraacetate was studied systematically by DFT theory.We also analyzed and compared the different electronic structures of metal carbenes and the bonding order of the metal-carbon bonds.Compared with gold carbene,the DFT results show that for the C-H bond insertion of phenol catalyzed by Cu-pybox,Cu-box and Rh-TC carbenes.The first step of nucleophilic addition is the decisive step of reactions.For the O-H bond insertion reactions,the step of [1,3]-H transfer is the rate-determining step.However,the energy barrier of nucleophilic addition is higher than the energy barrier of proton transfer,and due to weaker Rh-C and Cu-C bonds,Cu-pybox,Cu-box and Rh-TC ligands tend to dissociate into the solution followed by [1,3]-H transfers.Therefore,it is easier to obtain the C-H bond insertion reaction product catalyzed by Cu and Rh carbenes,which is consistent with the experimental results.2.In the transition metal carbene-catalyzed the O-H bond activation of phenols,water molecules can be used as proton transfer tools.Recently,control experiments of C-H intercalation of phenol and anisole catalyzed by gold-carbene have shown that there are significant differences between the deuterated products and hydrogenated products.We performed a further theoretical study on the function of water molecules of the C-H insertion reaction of phenols catalyzed by gold carbene.The calculated and experimental results show that water molecules play an important role in proton transport.In particular,phenol,as a weak acid,can exchange protons with water molecules,and then assist the proton transfer by water molecules.The H atoms of phenolic hydroxyl group can be transferred to the final C-H bond insertion product,which we call the “proton self-sufficient”(PSS)function of phenol.For anisole,it cannot provide protons.The protons of final C-H bond product are derived from its own C-H bond hydrogen atoms and hydrogen atoms of water molecule.The PSS function of phenol indicates that the presence or absence of proton donors of substrates can lead to differences in the final product.