Lithiated 1,3-Disilabicyclo[1.1.0]butanes Synthesized via Selective Cleavage of Exocyclic Si–Si Bonds on Bridgehead Silicon Atoms

Treatment of 1,3-di­(t-butyldimethylsilyl)-1,3-disilabicyclo­[1.1.0]­butane 1a with excess lithium in THF provided 1,3-dilithio-1,3-disilabicyclo[1.1.0]­butane 2 via reductive cleavage of the exocyclic Si–Si bonds
at the bridgehead silicon atoms. In the single crystals obtained by
recrystallization in the presence of 1,2-dimethoxyethane (DME), 2 exists as a solvent-separated ion pair, and its anionic
part forms an aggregate that contains three lithium atoms sandwiched
by two 1,3-disilabicyclo[1.1.0]­butan-1,3-diide units. Treatment of 2 with chlorotri­isopropylsilane provided triisopropylsilyl-substituted
1,3-disilabicyclo[1.1.0]­butane 1b. The structural characteristics
of 1b are close to that of the short-bond isomer, which
is consistent with previous theoretical predictions concerning the
steric effects of the bridgehead substituents on the structure of
silabicyclo[1.1.0]­butane.