Reactivity Studies of Germylene and Stannylene toward Various Boranes
Date Issued
2015
Date
2015
Author(s)
Chang, Che-Yuan
Abstract
Borane is a neutral molecule with three substituents and one empty p orbital. There are many applications of boranes in organic chemistry based on the Lewis acidity of the boron center. In order to enhance the electron deficiency of the molecule to improve reactivity, accumulation of the positive charges on boron is an effective way. One of the classes of boron mono-cation is borenium, which has two substituents and one neutral ligand. Compared to the extremely reactive borinium and over stabilized boronium, planar tri-coordinate borenium possesses moderate stability and reactivity for application in organic transformations. On the other hand, being the heavier analogues of N-heterocyclic carbene (NHC), N-heterocyclic metallylenes (NHEs, E = Si, Ge, Sn, Pb) have been investigated for decades. Metallylenes possess two active sites: a lone pair (Lewis base) and a vacant p orbital (Lewis acid). For heavier analogues, the poor s-p orbital mixing leads to increased Lewis acidity and decreased Lewis basicity at the metal center. Inspired by the reactivity of carbene-stabilized borenium cations, we decided to dedicate our efforts to replace carbon with other group fourteen elements, including germanium and tin. We propose that the metallylene-borane adducts could be synthesized, and followed by treating with particular hydride or halide abstracters would form the borenium moiety. However, preliminary results show that the reaction between metallylene and borane is highly dependent on the steric hindrance of both reagents. Thus far, metallylene either transferred its substituents to boron center or does not react with boron derivatives at all.
Subjects
metallylene
germylene
stannylene
boron
cation
borenium
Type
thesis
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