Reduction of a Bicyclo[1.1.0]tetrasil-1(3)-ene with LiAlH4 Leading to an Isolable Cyclotrisilenide

We report the reduction of bicyclo[1.1.0]tetrasil-1(3)-ene 1a, which has a bridgehead inverted Si═Si bond, with lithium aluminum hydride (LiAlH4) to provide the first isolable cyclotrisilenide 2. Single-crystal X-ray diffraction analysis revealed that 2 exists as a contact ion pair and the lithium cation was ligated by three THF molecules and the anionic silicon atom. The reaction of 1a with MeLi afforded the corresponding 1-methyl-3-lithiobicyclo[1.1.0]tetrasilane 3, which provides methyl-substituted cyclotrisilene 4 after protonation. These results suggest that 2 should be formed via the formal 1,2-addition of LiH to the bridgehead Si═Si bond of 1a and the subsequent intramolecular hydride migration accompanied by ring-opening. Cyclotrisilenide 2 readily reacted with Me3SiCl and Ph2PCl to afford the corresponding silyl and phosphanyl-substituted cyclotrisilenes, respectively.