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 tetraisobutyl alumoxane. In the first place, this is the production (at Ph₂Si(OH)₂ and Al(ⁱBu)₃ equimolar ratio) of oligomer alumoxanesiloxane structure with alternating four- and six-member rings, as well as isobutyl and phenyl groups migration between aluminum and silicon due to formation of intramolecular four-member cyclic alumosiloxane 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 alumosiloxane complex production, but the chain is terminated for the same reason, which in the case of Ph₂Si(OH)₂ reaction with tetraisobutylalumoxane results in failure of obtaining high-polymer alumosiloxane compounds. When Al(ⁱBu)₃ interacts with α- and γ-diols, no oligomer compounds are produced. Al(ⁱBu)₃ reaction with α, γ-diols results in monomer compounds that are likely to have cyclic structure. Notably at Al(ⁱBu)₃ interaction with α-diol only double excess of Al(ⁱBu)₃ allows full replacement of hydrogen in α-diol hydroxyl groups by aluminum alkyl residue with 1,3-bis(diisobutylalumoxymethyl)-1,1,3,3-tetramethyldisiloxane production. At 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 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 СН₂-groups between Si and 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 results in oligomer compounds.