An Authentic Al=Si Double Bond

Abstract Aluminatasilenes are the elusive heavier counterparts of the well‐known borataalkenes in which the B=C double bond is formally replaced by an Al=Si moiety. We report the isolation of a four‐membered anionic AlSi 3 cycle with a bona fide Al=Si double bond, which is obtained by the reaction of 2 eq. of disilenide Tip 2 Si=SiTipLi with H 2 AlCl (Tip=2,4,6‐triisopropylphenyl). X‐ray crystallography, UV/Vis spectroscopy and computational analysis confirm the double bond character with a very short Al−Si bond of 2.283(1) Å and high Wiberg bond index (WBI) of 1.31. Intramolecular C−H activation by the Al=Si bond and the reactions with sulfur sources confirm typical double bond reactivity.