Studies On Selective Acetoxylation And Chlorination Of O-carboranes Via B-H Activation

Carboranes are a class of boron hydride cluster compound with threedimensional aromaticity,carborane derivatives possess good thermal stability,oxidation and hydrolysis,which has significant application prospect in the luminescent material,medicinal chemistry and supramolecular chemistry.Therefore,regioselective synthesis of carbon and boron functionalized carboranes could achieve the more extensive application.Carboranes and polyhedral boranes decorated with polar groups such as hydroxyl or ester groups have been regarded as a new class of potential candidates of value.Halogenated compounds have always been as important intermediates to achieve functionalized boron.Based on this point,this paper carried out research on “ the selective acetoxylation and chlorination of o-carborane via B-H activation”,the main contents include the following two parts:The method to realized o-carborane B?9?and B?8?selective mono acetoxylation reaction via Palladium catalyzed/silver tuned with di?acetoxyiodo?benzene as the source of acetoxy group has been accomplished for the first time,and it is based on the characteristic that H-B?8,9,10,12?of o-carborane are inclined to electrophilic reaction.We proposed that silver acetate may play the role of lewis acid in the reaction system to achieve the coordination of B-H bond nearby,so as to hinder the formation of disubstitude to the maximum extent.With the results in hands,we present the reaction mechanism of Pd???/Pd???.This work represents the first example of regioselective construction of a cage B-H bond of o-carboranes via direct B-H acetoxylation.Based on the characteristic that B-H?8,9,10,12?of o-carborane are inclined to electrophilic reaction.Making using of tradition metal palladium catalyst,changing the role of FeCl₃ as a kind of lewis acid to promote reaction in carborane electrophilic halogenations,the solvent effect of acetic acid weakens the coordination between FeCl₃ and B-H bond,subsequently,FeCl₃ as chlorine source and the high degree of oxidation to complete the catalytic cycle of Pd???,only 2 mol % catalyst can be achieved with high yield B?9?and B?8?chlorination reaction.But the activation of B-Cl bonds to achieve carborane derivatives is still a great challenge.