Novel bifunctional periodic mesoporous organosilicas, BPMOs: Synthesis, characterization, properties and in-situ selective hydroboration - Alcoholysis reactions of functional groups

Abstract

A new class of bifunctional periodic mesoporous organosilicas (BPMOs) containing two differently bonded organic moieties in a mesoporous host has been synthesized and characterized. By incorporating bridge-bonded ethylene groups into the walls and terminally bonded vinyl groups protruding into the channel space, both the chemistry and physical properties of the resulting BPMO could be modified. The materials have periodic mesoporous structures in which the bridging ethylene plays a structural and mechanical role and the vinyl groups are readily accessible for chemical transformations. The vinyl groups in the material underwent hydroboration with BH3·THF and the resulting organoborane in the BPMO was quantitatively transformed into an alcohol using either H2O2/NaOH or NaBO3·4H2O. The materials retained ordered structures after subsequent in situ reactions with largely unchanged pore volumes, specific surface areas and pore size distributions. Other organic functionalized BPMO materials may be synthesized in a similar manner or by further functionalizing the resulting borylated or alcohol functionalized BPMO materials. The thermal properties of the BPMO materials have also been investigated and are compared to those of the periodic mesoporous organosilica (PMO) materials. Noteworthy thermal events concern intrachannel reactions between residual silanols or atmospheric oxygen and organics in BPMOs. They begin around 300°C and smoothly interconvert bridging ethylene to terminal vinyl groups and terminal vinyl to gaseous ethene and ethane, ultimately producing periodic mesoporous silica ar 900°C that exhibits good structural order and a unit-cell size decreased relative to that of the parent BPMO.