摘要
我們希望藉著這篇文章回顧本實驗室以理論計算方法探討氮雜環碳烯分子(N-heterocyclic carbenes，NHCs)及其相關化合物之性質的結果，並對這類分子做ㄧ個概括性的介紹。我們以imidazol-2-ylidenes (1)，imidazolin-2-ylidenes (2)，thiazo-2-ylidenes (3)及triazo-5-ylidenes (4)來加以比較。過去幾年本實驗室的研究工作主要在探討NHC 的各種特性，我們在NHC 一些定性性質的研究，如：單參重態能量差(singlet-triplet energy separation)，二聚合反應活化能(activation energy for dimerization)，1,2 氫轉移與分子間氫轉移反應等都有相當程度的涉獵與討論。除此之外，我們也將NHC 以配位基的形式鍵結於過渡金屬錯合物形成Cr(CO)_5L 及Ni(CO)_3L，利用鍵長、鍵能以及理論計算的C-O 振動頻率探討NHC 在過渡金屬上之電子特性的表現。近年來的實驗發現NHC 在有機的轉酯反應上有相當好的催化效果，因此我們以理論計算方式探討NHC 催化轉酯反應的反應路徑。
並列摘要
In recent years the efforts of our laboratory has mostly been concerned with the bonding characteristics of N-heterocyclic carbenes (NHCs). In this article we review results of our theoretical studies on the properties NHCs. These carbene molecules include imidazol-2-ylidene (1), imidazolin-2-ylidene (2), thiazo-2-ylidene (3), and triazo-5-ylidene (4). The singlet-triplet energy separation of carbenes, the activation energy for their dimerization, 1,2-hydrogen shift, and intermolecular hydrogen transfer have been examined via theoretical approaches. In addition, we studied the transition metal complexes [Cr(CO)_5L and Ni(CO)_3L] of NHCs, in which the geometrical parameters, bonding energies and computed C-O force constants were used to probe the electronic nature of NHC. Since NHC has been demonstrated to catalyze transesterification, we have also studied the mechanism of this important reaction.
延伸閱讀
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