乙硼烷及其同系物的σ芳香性

σ-aromaticity in Diborane and Its Congeners

本文从理论上证明缺电子乙硼烷及其同系物X_2H_6(X=B,Al,Ga)中的四元环具有四中心四电子(4c4e)的环状σ共轭体系,尽管看似与休克尔芳香性规则相悖,但具有σ芳香性;类似地,X2(CH3)6(X=B,Al,Ga)等缺电子甲基化合物也有σ芳香性,但其σ电子离域程度要比相应的氢化物略低;卤化物X_2Y_6(X=B,Al,Ga;Y=F,Cl,Br)中四元环的四中心八电子(4c8e)的σ骨架看似与具σ反芳香性的环丁烷相似,但其σ骨架电子均定域于各Y—Xσ配键,属非芳香性.

The four-membered rings （4MRs） of electron-deficient X2 H6 （X= B, AI, Ga） compounds, having a four-center four-elec- tron （4c4e） a-framework that seemingly conflicts with the （4n ＋2）e Htickel rule,are shown to be a-aromatic by means of density functional calculations.The methyl-substituted ones, X2 （CH3）6 （X= B, A1, Ga）, are also a-aromatic, but with a slightly lower degree of a electron delocalization than the corresponding hydrides. On the contrary, the 4MRs in the halogen-series X2 Y6 （X = B, A1, Ga; Y=F, C1, Br）, having a 4c8e a-framework seemingly similar to that of the σ-antiaromatic cyclobutane, are non-aromatic, as the ring a- electrons are localized within those Y-X dative bonds.