Syntheses and Reactivity Studies of Boron Cations
Date Issued
2015
Date
2015
Author(s)
Hsiao, Yu-Ting
Abstract
Boron cations are considered as stronger Lewis acid than neutral boranes. To further increase the electron deficiency of boron mono cation, few boron dications have been synthesized and structurally characterized. However, reactivity study of these boron dications has never been reported due to the presence of an over-stabilized boron center. Previously our group had synthesized a Cp*-substituted boron dication ([3][AlCl4]2), and discovered its unusual reaction with superhydride to yield a NHC-stabilized borabenzene (4). This result suggests that the incorporation of an electronically and coordinatively flexible substituent is imperative for realizing reactive boron dications. In this work, further reactivity studies of [3][AlCl4]2 and the synthesis of amino-substituted boron dication, [Cy2NB-IMes]2+, are reported. Reactions of [3]2+ with electrophiles, nucleophiles and reductants show that [3]2+ is more electron deficient than boron monocation and can be transformed into 4 through borylene intermediate. On the other hand, reaction of Cy2N-BCl2 with IMes in chlorobenzene directly gave the chloroborenium, [Cy2NB-IMes]+[Cl] ([6][Cl]). However, the second chloride abstraction of [6]+ was found to be difficult and remains unrealized.
Subjects
boron
boron cations
boron dications
borabenzene
N-heterocyclic carbene
Type
thesis