The Study On Activity Of Hydrides In B-N-H Compounds

Boron-nitrogen-hydrogen compounds?B-N-H compounds?are a class of boron-contained compounds constituted by B,N,H atoms.This type of compounds not only can be used as reducing agents to reduce aldehyde and ketone to the corresponding alcohol,but also can be used to synthesize other organic compounds and prepare new BN materials.In recent years,they have attracted considerable attention as hydrogen storage materials.In B-N-H compounds the hydrogen of B-H is hydridic and the hydrogen of N-H is protic.They can react with oppositely charged hydrogens and generate molecular H2.So far,the research of hydrogen storage materials of B-N-H compounds is focused on the performance of release hydrogen rather than chemical properties.In this work,we chose some B-N-H compounds and carried out research on the activity of the B-H bond.From this study,we can get useful information to design and synthesize new hydrogen storage materials.Hydrogen release when protic hydrogen atoms interact with hydridic hydrogen atoms,some new boron compounds can be obtained as well.In our previous study,we explored the reactions between hydridic hydrogen atoms and the protic hydrogen atoms.B-N-H compounds?ammonia borane,aminodiborane,N,N-dimethylaniline borane,alkali metal borohydrides?,reacted with the compounds which can provide protic hydrogen such as alcohols,phenols and acids:1)ammonia borane reacts with various phenols and organic acids;2)aminodiborane reacts with carboxylic acids,alkali metal hydrides;3)DMA·BH₃ and THF·BH₃ react with phenols;4)alkali metal borohydrides react with various alcohols.The reactions were monitored by 11B NMR spectroscopy and the products were characterized by NMR,FT-IR,single-crystal X-ray diffraction etc.In our study,the reactivity of B-H bond in the B-N-H compounds is different.We found that the reaction is not only related to the activity of B-H bond,but also affected by temperature,concentration,the molar ratio of reactants,solvents and other conditions.We also found that ammonia borane can react with organic acids which provide protic hydrogen?such as acetic acid,oxalic acid,chloroacetic acid,dichloroacetic acid,trichloroacetic acid,etc.?.At room temperature,only one substituted product can be obtained when ammonia borane reacts with acetic acid in organic solvent.However,different substituted products can be obtained when ammonia borane reacts with chloroacetic acid.First,we obtained the product in which one hydridic hydrogen is substituted by CH2CICOO-.When the reaction was completed,the first product can further react with chloroacetic acid.Second,we got the product in which two hydridic hydrogens were substituted.Compared with ammonia borane,the B-H bonds of DMA·BH₃ and THF·BH₃ are more active so that they can react with different phenols in THF solution,and generate polymer when DMA·BH₃ reacts with resorcinol.Aminodiborane can react with different acids,the four-membered ring is opened when it reacts with acetic acid.We can obtain metal complexes which have aminodiboranate anion when aminodiborane reacts with metal hydrides,and NaNH2?BH₃?2 can further react with MgBr2 to form the corresponding magnesium salts.LiBH₄ reacts with most of alcohols while NaBH₄only reacts with few alcohols because of their different solubility,and the different metal electronegativity of Li and Na.LiBH₄ or NaBH₄ can react with diols or triols very quickly,and produce a large amount of gas.