親電性鍺烯與錫烯之合成

Abstract

低價14族化合物同時具備路易士酸性與鹼性的性質，它的合成與對於小分子的活化反應是許多主族領域科學家研究的目標。其反應能力取決於其金屬烯中心孤對電子對與空p軌域的能量差。許多的研究聚焦在將氮取代基替換為矽或硼取代基來增加它的路易士酸性，但是目前尚未有人嘗試利用限制氮取代基孤對電子與中心金屬的空p軌域的作用，進而提升金屬烯的反應活性的研究。在本篇論文中，合成目標聚焦在鍺烯與錫烯，我們嘗試了兩種路徑來降低氮取代基的推電子能力，使中心金屬的空p軌域能量下降，進而提升其路易士酸性。一方面，我們嘗試合成多環金屬烯，利用橋頭氮上的孤對電子對無法與鍺烯、錫烯之空p軌域共平面的性質來降低N→M的π作用力；另一方面，我們認為將金屬烯嵌入反芳香性的環狀結構亦為提升其路易士酸性的方法之一，所以也嘗試製備了相關的、具有N-B-B-N結構的有機鋰試劑。

Apart from N-heterocyclic carbenes (NHCs), compounds consisting of isoelectronic low-oxidation state heavier Group 14 elements, the so-called metallylene, have been attractive targets for fundamental research because of their ambiphilic character that is critical for bond activations. On top of that, such capability of accepting and donating electrons simultaneously makes them potential candidates toward catalytic reactions that are normally mediated by precious transition metals. The efficiency for metallylene (R2E:) in chemical bond activation process is heavily dependent on the energy difference between the filled in-plan metal-centered lone pair and the remaining vacant p orbital of the central divalent Group 14 element. While most of the synthetic efforts towards reactive metallylenes were devoted to the replacement of amino substituents with silyl or boryl group, enhancing the electrophilicity of metallylene through manipulating the π-donating ability of amino substituents is less explored. Herein, we have investigated two strategies to lower the energy of the vacant p orbital of stannylene and germylene by mitigating the E→N π-interaction. On one hand, we plan to block the mesomeric effect of amino groups by tethering the two nitrogen atoms with a strained ring system. On the other hand, we envisage that the concept of antiaromatic metallylene would be a good way to boost the electrophilicity of the E(II) centers.