Synthesis of Siloxyalumoxanes and Alumosiloxanes Based on Organosilicon Diols

• Published in: Molecules (Basel, Switzerland) Switzerland), 2017-10, Vol.22 (10), p.1776
• Main Authors: Shcherbakova, Galina, Storozhenko, Pavel, Kisin, Alexander
• Format: Article
• Language: English
• Subjects: Aluminum; Crystallography, X-Ray; Diols; diphenylsilanediol; Hydroxyl groups; Migration; Molecular Structure; organoalumosiloxanes; Organosilicon Compounds - chemical synthesis; Organosilicon Compounds - chemistry; organosiloxyalumoxanes; Reaction products; Reagents; Siloxanes - chemical synthesis; Siloxanes - chemistry; Steric hindrance; tetraisobutylalumoxane; triisobutylaluminum; α-diol; γ-diol
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules22101776

We have drawn a few interesting conclusions while studying reaction products of Ph₂Si(OH)₂ with Al( Bu)₃ and tetraisobutylalumoxane. In the first place, this is the production (at a Ph₂Si(OH)₂ and Al( Bu)₃ equimolar ratio) of an oligomer siloxyalumoxane structure with alternating four- and six-member rings. In addition, it shows isobutyl and phenyl group migration between aluminum and silicon due to the formation of an intramolecular four-member cyclic complex [Ph₂(OH)SiO]Al( Bu)₂ → [( Bu)Ph(OH)SiO]Al( Bu)Ph. Ph₂Si(OH)₂ interaction with Al( Bu)₃ not only starts from intramolecular complex production, but the chain is terminated for the same reason, which in the case of the Ph₂Si(OH)₂ reaction with tetraisobutylalumoxane results in failure of to obtain high-polymer siloxyalumoxane compounds. When Al( Bu)₃ interacts with α- and γ-diols, no oligomer compounds are produced. In the Al( Bu)₃ reaction with α, γ-diols are created in monomer compounds that are likely to have a cyclic structure. Notably, when Al( Bu)₃ interacts with only α-diol, a double excess of Al( Bu)₃ allows for full replacement of hydrogen in the α-diol hydroxyl groups by aluminum alkyl residue with 1,3-bis(diisobutylalumoxymethyl)-1,1,3,3-tetramethyldisiloxane production. At an equimolar ratio of initial reagents, the second isobutyl radical at Al does not interact with the second hydroxyl group of α-diol, apparently due to the steric hindrance, and 1-(diisobutylalumoxymethyl)-3-(hydroxymethyl)-1,1,3,3-tetramethyl-disiloxane is produced. Al( Bu)₃ reactions with γ-diol also result in monomer compounds, but the presence of a chain consisting of three CH₂-groups between Si and the hydroxyl group facilitates interaction between the second hydroxyl group of γ-diol and the second isobutyl radical Al( Bu)₃. Tetraisobutylalumoxane reactions with α- and γ-diols result in oligomer compounds.