Study On Nido-Carborane B-H Bond Functionalization

nido-C₂B₉H₁₂^- is a carbon-hetero-boron cluster molecule composed of carbon,boron and hydrogen,containing 2 adjacent C-H bonds and 9 B-H bonds with similar chemical environment.Because of its unique geometric configuration and chemical properties,such as three-dimensional aromatics,rich boron content,hydrophilicity,nido-carboborane is widely used in biomedical molecules,luminescent materials,coordination chemistry and catalysis.Compared with the rapid development of closed-o-carborane B-H activation research,nido-carborane B-H activation research is still in the initial stage.Therefore,the B-H functional group reaction of nido-carboborane was studied in this paper.The main research contents and results are as follows:1.Based on the heteratomic-oriented B（11）-H bond activation strategy,a new"one-pot method"was developed to construct B-P and B-As bonds,and 28 nido-carborane derivatives were synthesized.The method has a wide range of substrates,triarylphosphine,alkyl diarylphosphine and trialkyl phosphine can all participate in the reaction.Guiding groups include pyridine,benzoxazole and diphenyl phosphine.The selectivity of the reaction site is high,and the single substituted product of a single site can be obtained with good yield without side reaction.2.Using 3-methylpyridinyl or quinoline group as the guiding group,a new palladium-catalyzed nido-carboboranes to construct B（6）-P bonds has been developed,and 20 nido-carboboranes have been synthesized.The novelty of the reaction lies in the specificity of the activation site.For the first time,the activation of the non-planar B（6）-H bond was achieved.Compatible with triarylphosphines containing electron-drawing and electron-donating groups and alkyl phosphines,heterocyclic arylphosphines also tolerate this reaction.3.A new palladium-catalyzed nido-carboborane B（2）-H bond enylation reaction has been developed using 3-methylpyridine as the guiding group and internal alkyne as the substrate.The reaction is compatible with internal aromatic alkynes of different electron-absorbing and electron-donating groups,including trifluoromethyl,methyl,trifluoromethoxy,tert-butyl,etc.This method has the advantages of mild reaction conditions and high site selectivity.