A Stable Neutral Compound with an Aluminum–Aluminum Double Bond

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.

过去数十年来，同双核多键合中性铝化合物——亦即烯烃的铝类似物——长期以来都是公认的极具挑战性的合成靶标。本文成功分离得到一种由氮杂环卡宾（N-heterocyclic carbenes）稳定的、具有Al=Al双键的稳定中性化合物。X射线晶体学与光谱学分析表明，该二铝单元具有反式平面构型，Al-Al键长为2.3943(16) Å，是目前已报道的分子态二铝物种中最短的键长。该新型化合物可与乙烯、苯乙炔发生反应，生成[2+2]环加成产物。研究团队还通过详细的密度泛函理论计算，对该化合物的结构与成键方式进行了深入探究。上述结果明确证实了该分子中存在Al=Al双键。