Abstract Some compounds containing the very bulky (Me 3) Si) 3 C group (= Tsi) attached to boron have been prepared. Treatment of the fluoride TsiB (F) OR (R=(CH 2) 4 Tsi) with LiAlH 4 in Et 2 O followed by hydrolysis gave TsiB (OH) OR, and treatment of the same fluoride with LiAlH 4 in THF gave a compound thought to be TsiBH 3 Li· 2THF. This compound was very air-sensitive and thermally unstable, decomposing at 50 C to give TsiH. It reacted ...