Theoretical Study On Thermodynamic Properties Of B-X Bond Of Organoboron Compounds Involved In The Reactions Catalyzed By Transition Metal

In recent years,the organic synthesis reaction of B-X activation of organoboron compounds catalyzed by transition metals has successfully attracted the interest of experimental chemists,and gradually become the hotspot of their research.These organoboron compounds mainly include the three hybrid types?sp,sp² and sp³?boronic acids,trifluoroborate salts,boronate esters,alkyl boron,the diboron?4?compounds with different structures such as B₂?OR?₄,B₂?SR?₄,B₂?NR₂?₄,B₂?alkyl?_n and B₂X₄,as well as the different types of aminoborane compounds,etc.Thus,in order to make the activation cleavage of the B-X bond of organoboron compounds better applied to the experimental studies by experimental chemist,we will use the quantum chemical calculation method to systematically study the B-X bond activation from the thermodynamic point of view.The main contents mainly focus on one of the thermodynamic constants which can measure the strength of the chemical bond,bond dissociation enthalpy?BDE?.This paper will provide a reliable theoretical basis for the dissociation enthalpy of the B-X bond of organoboron compounds by quantum chemical calculation.Firstly,we will select different series of high-precision methods to calculate the B-X bond dissociation enthalpy of organoboron compounds that the heavy?non-hydrogen?atoms are less than 8,and finally regard the averages of several high-precision methods which have good self-consistency as the standard reference values.Secondly,a variety of density functional theory?DFT?methods were selected to calculate the B-X bond dissociation enthalpy of these organoboron compounds that the heavy?non-hydrogen?atoms are less than 8,and correcte the results of theses DFT methods by the standard reference values,and compare their MD,MAD and RMSE values,thereby find out the best DFT method to calculate the B-X bond dissociation enthalpy.Finally,the B-X bond dissociation enthalpies of large systems were calculated by using this method,and the influence of substituent effect,position effect,frontier orbital energy,ring tension,molecular symmetry,etc.on the B-X bond dissociation enthalpy were further investigated.1.Firstly,we find out the highest accuracy DFT method to calculate the C-B bond dissociation enthalpy of organoboron compounds,that is M06-HF.Then studied the C-B bond dissociation enthalpy of three kinds of hybrid?sp,sp²,sp³?organoboron compounds by using this method.Among them,for the C?sp?-B BDE prediction,the ethynylboronic acids and ethynyltrifluoroborate salts were selected as the substrates.It is found that the electron-donating groups?EDGs?can decrease the C?sp?-B BDEs while the electron-withdrawing groups?EWGs?can increase the C?sp?-B BDEs.And the good linear relationships of the C?sp?-B BDEs of the two substrates with the difference(E_HOMO-E_LUMO)between the highest occupied molecular orbital?HOMO?and the lowest unoccupied molecular orbital?LUMO?of molecules as well as the singly occupied molecular orbital?SOMO?values(E_SOMO)of radicals were found.Secondly,for the C?sp²?-B BDE prediction,the substrates include?and?-substituted ethenyl boronic acids and ethenyl trifluoroborate salts,phenyl boronic acids and phenyl dioxaborinanes as well as typical five-membered and six-membered heterocyclic boronic acids?furan,thiophene,pyrrole and pyridine?etc.It is found that for the?and?-substituted ethenyl boronic acids and ethenyl trifluoroborate salts,when the substituents are consistent,the C?sp²?-B BDE change patterns are completely opposite.Moreover,it is obvious that the C?sp²?-B BDEs of phenyl dioxaborinanes are almost slightly higher than those of phenyl boronic acids,no matter the substituents are EDGs or EWGs and no matter the substituents are located at any position of the benzene.For the heterocyclic boronic acids,the ring size has a great impact on C?sp²?-B BDE values,and the C?sp²?-B BDEs of five-membered heterocyclic boronic acids are much higher than six-membered.Finally,for the C?sp³?-B BDE prediction,the substrates range from cyclopropylboronic acids and cyclopropyltrifluoroborate salts to cyclooctylboronic acids and cyclooctyltrifluoroborate salts.The results exhibit that the ring tension has a great effect on C?sp³?-B BDEs,and for the same ring size,the C?sp³?-B BDEs of boronic acids are higher than those of trifluoroborate salts.Moreover,there are two good linear relationships between C?sp³?-B BDEs and bond angles of both boronic acids and trifluoroborate salts.2.Secondly,it is found that the SOGGA11-X is the optimal DFT method to calculate the B-B bond dissociation enthalpy of diboron?4?compounds.Therefore,the B-B bond dissociation enthalpy of three kinds of diboron?4?compounds with different symmetries and different structures and the Pt-B and Cu-B bond dissociation enthalpy of transition metal boryl complexes under the catalysis of platinum and copper were investigated in-depth by using this method.Among them,for the first class of diboron?4?compounds,the substituents of-OR,-SR,-F,-Cl can increase the B-B BDE values while the substituents of-NR₂,-alkyl can decrease the B-B BDE values,and the radical-state effect?RE?has a stronger effect on B-B BDEs than the ground-state effect?GE?.Moreover,the absolute energy of SOMO is larger,the BDE value is higher.Next,for the second class of diboron?4?compounds,when the substituents on both sides are both-OR or-SR,the B-B BDE value is the largest,and when the substituents are-NR₂ or-alkyl,the B-B BDE value is the smallest.Also,when only one of the substituents is-OR or-SR,the B-B BDEs are relatively larger while when only one of the substituents is-NR₂ or-alkyl,the B-B BDEs are relatively smaller.Besides,the B-B BDE values are determined by the co-effects of GE and overall RE,and there is a excellent linear relationship between the B-B BDEs with the overall RE values.Then,by comparing the B-B BDEs of third class of diboron?4?compounds with the second class,it is found that the positions of the substituent have little influence on the B-B BDEs,and the RE plays a stronger role on the B-B BDEs than GE.Finally,for the transition metal boryl complexes,the results show that the participation of transition metals can make the B-B cleavages much easier.In addition,the frontier orbitals energy analysis demonstrates that the orbital energy effect of platinum complexes is more prominent than copper complexes,and there have good linear relationships between Pt-B and Cu-B BDEs with their corresponding E_HOMO-E_LUMO values.3.Finally,we found out the best method to calculate the B-N bond dissociation enthalpies of aminoborane compounds through screening and evaluation,namely M05-2X.Therefore,the B-N bond dissociation enthalpies of several different types of aminoborane compounds were calculated by using this method.As a result,it is found that for the first to fourth aminoborane compounds,when the substituents R₁ and R₂ on the N atom are fixed and the substituent on the B atom is-N?NH₃?₂,the B-N BDE value was decreased while the substituents on the B atom are-CH₃,-F and-Cl,the B-N BDE values were increased.Among them,the-F group is more favorable for the stability of B-N bond of aminoborane compounds than-Cl.But when the substituent groups R₃ and R₄ on the B atom are fixed,the order of contribution of the substituent groups-CH₃,-Si H₃ and-H on the N atom for the stability of aminoborane compounds is as follows:-H>-Si H₃>CH₃.And for these four kinds of aminoborane compounds,the B-N bond lengths are longer,the B-N BDE values are lower,on the contrary,the B-N bond lengths are shorter,the B-N BDE values are higher.In addition,for the B-N BDE values of cyclic aminoborane compounds,it is found that the ring size has almost no effect on the B-N BDE values,but the heteroatoms and the positions of heteroatoms have a great effect on the B-N BDE values.Moreover,the B-N BDE values also decreased overall as the B-N bond lengths increased.