3 years ago

Synthesis of Siloxyalumoxanes and Alumosiloxanes Based on Organosilicon Diols.

Alexander Kisin, Galina Shcherbakova, Pavel Storozhenko
We have drawn a few interesting conclusions while studying reaction products of Ph₂Si(OH)₂ with Al((i)Bu)₃ and tetraisobutylalumoxane. In the first place, this is the production (at a Ph₂Si(OH)₂ and Al((i)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((i)Bu)₂ → [((i)Bu)Ph(OH)SiO]Al((i)Bu)Ph. Ph₂Si(OH)₂ interaction with Al((i)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((i)Bu)₃ interacts with α- and γ-diols, no oligomer compounds are produced. In the Al((i)Bu)₃ reaction with α, γ-diols are created in monomer compounds that are likely to have a cyclic structure. Notably, when Al((i)Bu)₃ interacts with only α-diol, a double excess of Al((i)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((i)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((i)Bu)₃. Tetraisobutylalumoxane reactions with α- and γ-diols result in oligomer compounds.

Publisher URL: http://doi.org/10.3390/molecules22101776

DOI: 10.3390/molecules22101776

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