B(C6F5)3-Catalyzed Hydroboration of Alkenes with N-Heterocyclic Carbene Boranes via B—H Bond Activation

摘要

In this work,a novel mode for the activation of N-heterocyclic carbene boranes (NHC-boranes) was developed by generating the highly reactive zwitterion species through hydride abstraction with Lewis acid B(C6F5)3 in an frustrated Lewis pairs manner.A broad range of alkenes including stilbenes,β-methylstyrenes,styrenes,and alkyl-alkenes were suitable substrates for the B(C6F5)3-catalyzed hydroboration to furnish the desired products in good to high yields.Significantly,excellent regioselectivities were obtained in some cases.Mechanistic studies indicate that the B—H bond cleavage is likely involved in the rate-determining step.In addition,an elec-trophilic addition of NHC-borenium cation to alkenes and the subsequent formation of carbocation are also postulated.The current work provides a promising method for the activation of stable borane adducts,which might lead to some interesting transformations in the future.