Stabilization of organosilanetriols in amine matrices: trapping intermediates between RSi(OH)₃ and (RSiO₃)^3- anions

Abstract

Unless kinetically stabilized, hydroxides of silicon are unstable and readily self-condense through elimination of water molecules to yield Si-O-Si siloxane linkages. The condensation reaction is known to be very facile in the presence of acids and bases. Stabilization of three hydroxyl groups on the same silicon in acidic or basic medium assumes importance, in view of their use in the rational synthesis of metallosilicates. In the present work, the first examples of a silanetriol stabilized in a matrix of aliphatic or aromatic diamines are described. The reactions of [2,6-Me₂C₆H₃N(SiMe₃)Si(OH)₃] (1b) with equimolar amounts of piperazine (PIP), 1,4-diazabicyclo[2,2,2]octane (DABCO), and 4,4'-bipyridine (BPY) yield [{2,6-Me₂C₆H₃N(SiMe₃)Si(OH)₃}{PIP}] (2), [{2,6-Me₂C₆H₃N(SiMe₃)Si(OH)₃}{DABCO}{1,4-dioxane}_0.5] (3), and [{2,6-Me₂C₆H₃N(SiMe₃)Si(OH)₃}{BPY}_1.5] (4), respectively. These assemblies have been characterized by elemental analysis, IR and NMR (¹H and ¹³C) spectroscopy, and single-crystal X-ray diffraction techniques. Apart from providing an insight into the association behavior of silicon polyhydroxides in basic medium, this study also offers clues for the stabilization of metastable orthosilicic acid, Si(OH)₄, in an organic soluble medium.