Synthesis and Reactivity of Aluminum Disilacyclopropenes. Cyclic AlSi₂ Delocalized 2π Systems

The synthesis, structures, and reactivity of the first unsaturated AlSi₂ three-membered ring systems were described. Reactions of dilithiodisilene [(NHB)LiSi═SiLi(NHB)] (1, NHB = diazaborolyl) with aluminum halides AlCl₃, Ar(SiMe₃)NAlCl₂ (Ar = 2,6-iPr₂C₆H₃), Cp*AlBr₂ (Cp* = C₅Me₅), and TipAlBr₂·Et₂O (Tip = 2,4,6-iPr₃C₆H₂) led to the formation of AlSi₂ three-membered ring species, solvated (NHBSi)₂AlCl(OEt₂) (2) and solvent-free (NHBSi)₂AlN(SiMe₃) Ar (3), (NHBSi)₂AlCp* (4), and (NHBSi)₂AlTip (5), in good yields. X-ray diffraction studies and DFT calculations disclosed delocalized AlSi₂ 2π electron systems. Methanolysis of 4a resulted in cleavage of the Al-Si σ and Si-Si π bonds, giving trihydrodisilane (NHB)H(MeO)SiSiH₂ (NHB) (6). Reaction of 4b with 4 equiv of N₂O and H₂C═CH₂ resulted in the insertion of four oxygen atoms and four H₂C═CH₂ π bonds into all of the Al-Si and Si-Si bonds, yielding the O- and CH₂CH₂-bridged polycyclic species 7 and 8, demonstrating the synergistic reactivity of the Al-Si and Si-Si bonds in the AlSi₂ ring system.