The Study Of Selective Activation And Functionalization Of Carborane C-H Or B-H Bond

Carboranes are widely applied in the field of catalysis,functional materials,medicine supramolecules and coordination chemistry,owing to their useful properties such as enriched boron content,good thermo-and chemical stability,and three-dimensional geometric feature.Therefore,developing new efficient methodologies for direct C/B-H functionalizations of o-carborane is very important area of research.Literature reports and DFT calculation shows that carboranes can be viewed as three-dimensional benzene analogues since the 26 electrons are delocalized overall the cluster.Although the methods of direct ortho C(sp2)-H activation/functionalization are well known,the selective and direct cage B-H activation/functionalization of carborane is much less explored,which need to be explored further.Of course,These protocols in C(sp2)-H activation/functionalization also bring inspirations to us.Up to date,the site-selectivity of cage B-H bonds have been achieved through the unique electronic features,steric effect and directing group etc.However,in that of B(4,5,7,11)positions,which are rather difficult to functionalize by tuning the electronic effects.Now,to assemble a new directing group,which can site-selectively activate cage B-H bonds via cyclometallation,can break through these limitations and direct cage B(4,5)-H activation to produce B-C,B-O and B-N bonds.Note that,the other B-X couplings are still absent.Therefore,more directing groups with high performance,various substrates with diversities,and robust methods for B—H activation/functionalization are still to be explored in the field.The contents cover the following two parts:(1)Base-Promoted Decarboxylative Azo-Coupling:Construction of Unsymmetrical AzocarboranesIn this chapter,base promoted decarboxylative azo couplings of carboranyl carboxylic acids with diazo salts have been developed to provide a series of trans azocarboranes in moderate to excellent yields with good functional group tolerance.For example,the diazo salts including active hydrogen,acid sensitive and heterocyclic ones successfully underwent azo coupling reaction as well.This reaction could proceed at room temperature in open air and circumvent the use of expensive catalyst,oxidant or ligand.Besides,innocuous CO2 as a by-product won't cause serious pollution to the environment;o-carborane,the other by-product,can be recycled.In addition,this methodology could be efficiently scaled up,which can offer a large amount of substrates for the following B-H functionalization.(2)Iridium(?)-Catalyzed Selective Sulfonamidation of o-Carborane with Sulfonyl Azide by Carboxylic Acid-Assisted B(4)-H Bond ActivationThe cage B-H sulfonamidation of o-carborane directed by carboxylic acid group was reported.The optimum condition is {2.5 mol%[IrCp*Cl2]2/10 mol%AgNTf2/1.5 equiv NaOAc/DCE/85?/Ar/10 h}.This reaction systerm do not need the extra oxidants because sulfonyl azides can work as innherent oxidants through N-N2 bond cleavage.In addition,aryl,polyaromatic,heterocyclic,aliphatic sulfonyl azides successfully undergo the selective sulfonamidation with carboranyl carboxylic acids in high yields with excellent functional group tolerance.Notably,the reactions possess excellent site-selectivity and also provide merely mono-sulfonamidated products in all cases.In particular,cage B(4)-aryl amination,even alkyl amination was also realized for the first time by using aryl and aliphatic azides as the nitrenoid sources.