Synthesis of Siloxyalumoxanes and Alumosiloxanes Based on Organosilicon Diols

摘要

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