Homodinuclear multiple-bonded neutral Al compounds, aluminum analogues of alkenes, have been a notoriously difficult synthetic target over the past several decades. Herein, we report the isolation of a stable neutral compound featuring an Al═Al double bond stabilized by N-heterocyclic carbenes. X-ray crystallographic and spectroscopic analyses demonstrate that the dialuminum entity possesses trans-planar geometry and an Al–Al bond length of 2.3943(16) Å, which is the shortest distance reported for a molecular dialuminum species. This new species reacts with ethylene and phenyl acetylene to give the [2+2] cycloaddition products. The structure and bonding were also investigated by detailed density functional theory calculations. These results clearly demonstrate the presence of an Al═Al double bond in this molecule.

中文翻译：

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具有铝-铝双键的稳定中性化合物

在过去的几十年中，全烯烃多键合中性Al化合物（烯烃的铝类似物）一直是合成目标中非常困难的目标。本文中，我们报道了一种稳定的中性化合物的分离，该化合物具有被N-杂环卡宾稳定的Al═Al双键。X射线晶体学和光谱分析表明，二铝实体具有反式-平面几何形状，Al-Al键长为2.3943（16）Å，这是报道的分子二铝物种的最短距离。该新物质与乙烯和苯基乙炔反应，生成[2 + 2]环加成产物。还通过详细的密度泛函理论计算研究了结构和键合。这些结果清楚地证明了该分子中存在Al═Al双键。