Synthesis of Siloxyalumoxanes and Alumosiloxanes Based on Organosilicon Diols.

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.