Theoretical Study On Thermodynamic Properties Of Trifluoroborate Anions And Selenols

In recent years,the application of organotrifluoroborate salts?Exists as anions insolution?and selenol compounds in organic synthesis reactions has greatly attracted the interest of experimental chemists and has gradually become a research hotspot in experiments.The organotrifluoroborate anions mainly includes C_sp3-hybridized center organotrifluoroborate anions?R-CH₂-BF₃^-?and the C_sp2-hybridized center vinyltrifluoroborate anions,the organotrifluoroborate anions of the C_sp3hybrid center include allyltrifluoroborate anions,2-propynyltrifluoroborate anions,benzyltrifluoroborate anions and heterocyclmethyltrifluoroborate anions.The cross-coupling of C_sp3-hybridized center organotrifluoroborate salts has been achieved successfully by single-electron transfer?SET?in the novel dual catalytic Suzuki-Miyaura reactions.For organselenol compounds?R-Se H?mainly include alkylselenols,cycloalkylselenols,benzylselenols,allylselenols,and arylselenols,and organselenol compounds play an important role in both chemistry and biochemistry.In the novel dual catalytic Suzuki-Miyaura reactions of organotrifluoroborate anions and the synthesis of organic organselenol compounds,the strength of C-B bond and Se-H bond plays an important role in understanding their reactivity,so the activation and fracture of chemical bond is a key step.Therefore,in order to make the active cleavage of the chemical bond of theorganotrifluoroborate anions and the organselenol compounds to provide a better guidance for experimental researchers,we have used the theoretical method of quantum chemistry to systematically study and analyze the activation fracture of C-B bond and Se-H bond from the perspective of thermodynamics.The research contents mainly include the E°of organotrifluoroborate anions and the dissociation equilibrium constant p Ka of the organselenol compounds.The details are as follows,for the organotrifluoroborate anions,in the first step,we selected 27 organtrifluoroborate anions in which no more than 8non-hydrogen atoms are included as the training set,two different series of composite high-level ab initio methods includes Gn series and CBS series were employed to calculate the?Ggas values of these 27 organtrifluoroborate anions.As these 27?Ggas experimental values are unknown,we finally use the average value of several composite high-level ab initio methods with good self-consistency as the standard reference value for the DFT evaluation in subsequent studies.In the second step,more than a dozen density functional theory?DFT?methods were selected to calculate the?Ggas values of organtrifluoroborate anions,among these density functional theory?DFT?methods,a suitable method was chosen for larger organotrifluoroborate anions systems?for organtrifluoroborate anions with a heavy?non-hydrogen?atoms greater than 8?.Among these DFT methods,there are some long-range corrections such as w B97XD and some methods appearing after 2010such as M11 were used.Then we compared the mean deviation?MD?,mean absolute deviation?MAD?and root mean square error?RMSE?between the?Ggas values calculated by different DFT methods and the standard reference values,and the most accurate and suitable method for the calculation of larger organotrifluoroborate anions systems was selected.After that,the solvation model was determined.We used the most appropriate DFT method in combination with the solvation model PCM?including six atomic radii models?and the SMD model to perform the calculation of standard redox potentials of 24 organtrifluoroborate anions with experimental values.In the end,the mean deviation?MD?,mean absolute deviation?MAD?and root mean square error?RMSE?obtained from the results calculated by different protocols and the experimental values were compared,and an optimal protocol for calculating standard redox potentials was selected.Finally,the optimal protocol was employed to systematically study the standard redox potentials of various types of organtrifluoroborate anions,and the effect of the different factors such as substituent effects,orbital energy effects,and position effects on standard redox potentials were further investigated.Secondly,for organselenol compounds,two DFT methods combined with three solvation models were used to calculate the p Ka values of 16 organselenol compounds with experimental values,and the MD,MAD and RMSE values were compared between the calculated results and the experimental values.The optimal combination protocol was finally selected to systematically study the p Ka values of various types of organselenol compounds,and the substituent effects of selenol compounds were further explained by NBO analysis.1.For the calculation of the standard redox potentials of organtrifluoroborateanions,we first adopted seven high-level methods including G3,G4,G3B3,G4MP2,CBS-Q,CBS-QB3,and CBS-4M to calculate the?G_gasvalues of organtrifluoroborate anions with no more than 8 non-hydrogen atoms are included and the experimental value is unknown.By comparing the calculation results,the averages of six high-level methods including G3,G3B3,G4,G4MP2,CBS-QB3 and CBS-4M were used as standard reference values for subsequent calculations.After that,17 DFT methods were employed to calculate the?G_gasvalues of 27 organtrifluoroborate anions with no more than 8non-hydrogen atoms are included.Among them,the M05-2X method stands out with the smallest RMSE value of 1.58kcal/mol,which is considered to be the most suitable method for the calculation of the organtrifluoroborate anion system.Finally,the M05-2X method in combination with the SMD model as well as the PCM model with 6 atomic radii model including UAHF,UAKS,Bondi,UA0,UFF and Pauling were employed to calculate the standard redox potentials of 24 organtrifluoroborate anions with experimental values.The results show that the combination of the M05-2X method and the PCM model with the UAHF atomic radius provides the best the highest precision with the smallest RMSE value of 0.16V.Therefore,the standard redox potentials and substituent effects of C_sp3-hybridized center organotrifluoroborate anions?R-CH₂-BF₃^-,R=alkenyl,alkynyl,aryl and heterocyclyl?as well as the C_sp2-hybridized center vinyltrifluoroborate anions were studied by using this theoretical protocol.Among them,for R=alkenyl,comparing with?-substituted allyltrifluoroborate anions,the standard redox potential value differences of?-substituted between EWGs and EDGs are smaller.For R=alkynyl,there are three particular standard redox potential values of the EDGs of-OCOCH₃,-NHCOCH₃and-OPh for both?-and?-substituted 2-propynyltrifluoroborate anions.For R=aryl,there are three particular standard redox potential values of-OCOCH₃,-NHCOCH₃and-NHPh for?-substituted benzyltrifluoroborate anions,and for ortho-,meta-and para-substituted,the remote position effects are not obvious.For R=heterocyclyl,generally,the standard redox potential values of six-membered heterocyclmethyltrifluoroborate anions are larger than five-membered heterocyclmethyltrifluoroborate anions.In the C_sp2center vinyltrifluoroborate anions,for?-substituted,the higher redox potential values are found in EWGs of-NO₂,-CHO,-CF₃and-F as well as EDG of-OCOCH₃and the EDGs of-Ph,-NHPh,-N?CH₃?₂and-NHCH₃can decrease the redox potential values.Furthermore,we analyzed the natural bond orbital?NBO?,the ground-state effect?GE?,the radical-state effect?RE?as well as the energies of frontier orbitals to further reveal the essence of the redox potential value change patterns.Among different types of organtrifluoroborate anions,the linear relationships between the standard redox potential values and the substituent constant?_p⁺,GE values and RE values were obtained.2.For the calculation of the p Ka values of the organselenol compounds,weadopted the conformation of the organselenol compound combined with three water molecules,and two kinds of DFT methods including the M06-2X and?B97XD methods and three solvation models including the SMD model,SMD_{s SAS}model and the PCM-Bondi model were used to calculate the p Ka values of 16 organselenol compounds with experimental values.By comparing the calculation results,it is found that the?B97XD method combined with the SMD model is the best protocol with the smallest RMSE value of 0.38 p K units for the calculation of the p Ka values of organselenol compounds.Therefore,the p Ka values and substituent effects of various types of organselenol compounds?R-Se H?and organselenocarboxylic compounds?R-COSe H?were investigated with this protocol,where R=alkyl,cycloalkyl,benzyl,allyl and aryl.The results indicate that for the same type of organselenol and organselenocarboxylic acid compouns,the p Ka values of the organselenocarboxylic acid compounds are higher than the p Ka values of the organselenol compounds.In general,the electron-withdrawing groups?EWGs?can decrease the p _Ka values,and the electron-donating groups?EDGs?increase the p Ka values.However,because it is may be because substituents of-COOH,-NH₂and-N?CH₃?₂exist in the form of ionic configuration in aqueous solution,they will have opposite effects on the p Ka values of some types of selenol compounds,the EWG of-COOH increases the p Ka value,while EDGs of-NH₂and-N?CH₃?₂decrease the p Ka value.In addition,the good linear relationships between the p Ka values and the natural charges of the Se atoms in the radicals,E_HOMOvalues and so on were found in different types of organselenol and organselenocarboxylic acid compounds.