DFT Study On Reaction Mechanism Of Boride Reduction Of Carbonyl Compounds

Boron atoms are located near carbon atoms in the periodic table,and the configuration of boron valence electrons is 2s²2p¹.Since it contains an empty p orbital in the valence shell,the number of valence electrons is less than the number of valence orbitals,which is called an electron-deficient atom.An electron on 2s of boron atom is excited to the 2p orbital and still has an empty p orbital,so it's very receptive to electron pairs.Boron atoms have a relatively high ionization potential(I,8.30 e V;II,25.15 e V;III,37.92e V),so it is very difficult to form B³⁺ions after losing electrons.Thus,boron compounds usually exist as covalent bonds.The complexity of boron and its compounds in structure and the diversity of bond types enrich and expand the existing covalent bond theory,so the research on boron and its compounds has been developed rapidly in recent years.Boron compounds play an important role in the reduction of carbon-carbon double bond and carbon-oxygen double bond.It has been one of the hot topics in the field of chemistry and has received more and more attention.The efficient boron-containing catalyst and reducing agent bring a new breakthrough for the reduction of carbon-carbon double bond and carbon-oxygen double bond,the improvement and design on this basis may further improve the yield,and the establishment of catalytic mechanism will provide a more reliable theoretical basis for this type of reaction.However,although researchers try to explore the mechanism of reaction by experimental means,it is often difficult to fully capture the intermediates of reaction due to the limitation of experimental means,which leads to the controversy of such reaction mechanism.With the rapid development of science and technology,theoretical computational chemistry plays an increasingly important role in the study of molecular structure,properties and reaction mechanism,and the Density Function Theory(DFT)has been gradually developed,which can well solve the problems in ab initio calculation.On the basis of density functional theory,the theory and calculation method of quantum chemistry have been improved.We can theoretically simulate the reaction process by combining quantum chemical calculation with chemical theoretical knowledge.Therefore,this paper uses density functional theory(DFT)calculations to reveal the microscopic reaction mechanism of carbon-carbon double bonds and carbon-oxygen double bonds of boron-containing compounds for catalytic reduction,to provide theoretical guidance for the design of new and efficient catalysts.In this paper,the reaction mechanism of boron-containing compounds in the reduction of carbon-oxygen double bond is systematically studied by using the quantum chemical calculation method,and the following conclusions are drawn:1.For the reduction of traditional carbonyl compounds,aminoborane(NH₃BH₃,AB)and N-methylaminoborane(M_nAB)are effective reductants.However,due to the uncertainty of the reaction process,different reaction mechanisms have been put forward.However,the solvent effect,which is closely related to the reaction mechanism,has not been paid much attention.In this work,the reaction mechanism of aminoborane(AB)and N-methylaminoborane(M_nAB)stoichiometric reduction of carbonyl compounds was comprehensively studied by DFT method.The results show that in aprotic solvent(THF)and protic solvent(Me OH),the free energy of synergistic dihydrogen transfer process is 4.7 kcal/mol lower than that of borohydride reaction,which indicates that the reaction of AB reducing carbonyl compound tends to synergistic dihydrogen transfer.For the reduction of carbonyl compounds by M_nAB,the free energy of the corresponding reactions was higher than that of AB,and the reduction of carbonyl compounds by M_nAB(n=1,2)was more inclined to cooperate with dihydrogen transfer than with borohydride reaction.2.Borohydride reaction of CO₂ is widely used as one of the most useful methods to reduce CO₂.The catalyst also changed from the synthesis of noble metal complexes to the synthesis of cheap and environmentally friendly alkali metal complexes.However,in order to promote the industrial development of this field,it is still necessary and challenging to find a more effective,cheaper and more environmentally friendly catalytic reduction system for activated CO₂ molecules.In this work,the alkaline earth metal magnesium hydrogenated boric acid derivative was used as catalyst by DFT method,and the borohydride(HBpin)as reducing agent.Highly selective reduction and borohydride reaction of CO₂were carried out,and the reaction mechanism was studied in detail.The results show that compared with the generally accepted mechanism,the reaction between HBpin and alkali metal magnesium carboxylic acid derivatives is more likely to occur.HBpin and alkali metal magnesium carboxylic acid derivatives coordinate to form a six-membered ring,which can indirectly remove formaldehyde,and then HBpin can reduce formaldehyde to methanol.