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The synthesis, structures, and reactivity of the first unsaturated AlSi 2 three-membered ring systems were described. Reactions of dilithiodisilene [(NHB)LiSi═SiLi(NHB)] ( 1 , NHB = diazaborolyl) with aluminum halides AlCl 3 , Ar(SiMe 3 )NAlCl 2 (Ar = 2,6- i Pr 2 C 6 H 3 ), Cp*AlBr 2 (Cp* = C 5 Me 5 ), and TipAlBr 2 ·Et 2 O (Tip = 2,4,6- i Pr 3 C 6 H 2 ) led to the formation of AlSi 2 three-membered ring species, solvated (NHBSi) 2 AlCl(OEt 2 ) ( 2 ) and solvent-free (NHBSi) 2 AlN(SiMe 3 ) Ar ( 3 ), (NHBSi) 2 AlCp* ( 4 ), and (NHBSi) 2 AlTip ( 5 ), in good yields. X-ray diffraction studies and DFT calculations disclosed delocalized AlSi 2 2π electron systems. Methanolysis of 4a resulted in cleavage of the Al-Si σ and Si-Si π bonds, giving trihydrodisilane (NHB)H(MeO)SiSiH 2 (NHB) ( 6 ). Reaction of 4b with 4 equiv of N 2 O and H 2 C═CH 2 resulted in the insertion of four oxygen atoms and four H 2 C═CH 2 π bonds into all of the Al-Si and Si-Si bonds, yielding the O- and CH 2 CH 2 -bridged polycyclic species 7 and 8 , demonstrating the synergistic reactivity of the Al-Si and Si-Si bonds in the AlSi 2 ring system.

A new strategy for the highly selective synthesis of tricyclo[2,2,0,0 2,5 ]hexasilanes R 6 Si 6 X 2 (R = 2,4,6-Me 3 C 6 H 2 ; X = H, Cl) and a bridged tricyclic R 6 Si 6 dianion starting from the tetrachlorotrisilane RCl 2 SiSi(H)RSiCl 2 R (1) was described. Reduction of 1 with lithium naphthalene afforded tricyclohexasilane R 6 Si 6 H 2 (2), which was halogenated to give the dichloride R 6 Si 6 Cl 2 (3). Reduction of 3 with four equivalents of potassium graphite in the presence of 18-crown-6 afforded the first R 6 Si 6 dianion (5) paired with [K(18-crown-6)] + 2 counterions. The dianion 5 could act as a two-electron reductant toward transition metal halides and a nucleophile toward chlorosilanes. These reactions allowed the efficient and selective access to three types of silicon cages. The structures of the representative cages were confirmed by X-ray diffraction studies. Density functional theory calculations on 5 indicate that the negative charges are localized mainly on the anionic silicon atoms.

Stable compounds with a boron-chalcogen (S or Se) valence double bond have been prepared via sequences involving insertion of the chalcogen into a B-H bond and subsequent hydrogen migration. X-ray diffraction studies and density functional theory calculations on the resulting compounds provide convincing evidence for the boron-chalcogen multiple bonding.