SOMC grafting of vanadium oxytriisopropoxide (VO(OiPr)3) on dehydroxylated silica; analysis of surface complexes and thermal restructuring mechanism.

by Manuel P Högerl, Li Min Serena Goh, Edy Abou-Hamad, Samir Barman, et.al.
Year: 2018 DOI: https://doi.org/10.1039/C8RA02419G

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RSC advances

Abstract

Vanadium oxytriisopropoxide (VO(OiPr)3), 1, was grafted on highly dehydroxylated silica (SiO2-700: aerosil silica treated at 700 °C under high vacuum) to generate compound 2 following the concepts and methodology of surface organometallic chemistry (SOMC). The resulting compound was analyzed by elemental analysis, FT-IR, 1H, 13C and 51V solid state (SS) NMR, Raman and EPR spectroscopies. The grafting reaction of 1 to generate 2 was found to lead to the formation of a monopodal surface complex [([triple bond, length as m-dash]Si–O–)V(O)(OiPr)2], 2m, as well as bipodal [([triple bond, length as m-dash]Si–O–)2V(O)(OiPr)], 2b, formed along with ([triple bond, length as m-dash]Si–O–iPr) moieties as an effect of the classical rearrangement of 2m with strained siloxane bridges. Upon controlled thermal treatment at 200 °C under high vacuum, 2m and 2b were found to mainly rearrange to tetrahedral VO4 moieties [([triple bond, length as m-dash]Si–O–)3V(O)] (3) with formation of propylene whereas the ([triple bond, length as m-dash]Si–O–iPr) groups were preserved. The mechanism of the thermal rearrangement of the isopropoxide groups was investigated by a DFT approach revealing the occurrence of a concerted γ-H-transfer and olefin elimination mechanism.