Sequential hydroboration-alcoholysis and epoxidation-ring opening reactions of vinyl groups in mesoporous vinylsilica

Tewodros Asefa, Michal Kruk, Mark J. MacLachlan, Neil Coombs, Hiltrud Grondey, Mietek Jaroniec, Geoffrey A. Ozin

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Abstract

We report the sequential transformation of vinyl groups into hydroborate and alcohol as well as vinyl into epoxide and diol functional groups in hexagonal mesoporous vinylsilica materials, denoted meso-vinyl-SiO2. The first transformation proceeds quantitatively through the hydroborylated derivative. After appropriate quenching, the hydroborylated materials are stable at ambient conditions and can undergo transformation into alcohols and various other functional groups. The pore volume and pore size uniformity were found not to be greatly affected by quenching of the hydroboranes with methanol, but they were reduced by quenching with water due to the deposition of boron-containing species in the channels. Complete conversion of hydroborylated materials to alcohol-functionalized materials required basic conditions and treatment time of several hours. Although this led to a significant structural shrinkage, decrease in pore volume, and decrease in ordering, there was no evidence of a partial collapse or removal of substantial parts of the pore walls under optimized synthesis conditions. This is the first successful conversion of organic groups of a functionalized ordered mesoporous silica host in alkaline solution, conditions known to be detrimental for silica frameworks. Epoxidation of the vinyl groups and subsequent conversion of the resulting epoxides into diols are also briefly described. The chemical transformation through epoxidation affords ordered mesoporous silica materials functionalized with potentially chiral organic groups, which could find applications in asymmetric catalysis and chiral separations. It was found that the epoxidation was slower than hydroboration and resulted in a lower degree of conversion. These two examples of hydroboration-alcoholysis and epoxidation-ring opening reactions of terminally bonded vinyl groups in meso-vinyl-SiO2 demonstrate the novel concept of sequential organic chemical transformations harbored inside the ordered channels of mesoporous organosilica materials.

Original languageEnglish (US)
Pages (from-to)447-456
Number of pages10
JournalAdvanced Funtional Materials
Volume11
Issue number6
DOIs
Publication statusPublished - Dec 1 2001
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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