A coordination
complex, lithium hepta(i-butyl)silsesquioxane
trisilanolate (1; Li-T7), a stable intermediate
in silsesquioxane (SQ) syntheses, was successfully isolated in 65%
yield and found to be highly soluble in nonpolar solvents such as
hexane. The structure of Li-T7 was confirmed by NMR, IR
spectroscopy, matrix-assisted laser desorption ionization time-of-flight
mass spectrometry, electrospray ionization mass spectrometry, and
computational simulation, providing detailed elucidation of the intermolecular
self-association of the SQ cage with a box-shaped Li6O6 polyhedron through strong coordination bonds. After acid
treatment, Li-T7 undergoes lithium–proton cationic
exchange, yielding hepta(i-butyl)silsesquioxane trisilanol
(2; H-T7) quantitatively. The high yield of
H-T7 seems to be influenced by Li–O bonding in the
Li-T7 complex that affects the selective formation of hepta(i-butyl)silsesquioxane trisilanolate and the bulky i-butyl groups which may prevent decomposition or SQ cage-rearrangement
even at reflux under alkaline conditions. Single-crystal X-ray crystallography
confirms the presence of the dumbbell-shaped SQ partial cages through
strong intermolecular hydrogen bonds. Interestingly, lowering the
polarity of the reaction solution by adding dichloromethane results
in formation of the cubic octa(i-butyl)silsesquioxane
(3; T8) cage in a good yield (47%), which
is isolated by crystallization from the reaction solution.