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Interaction of Water, Alkyl Hydroperoxide, and Allylic Alcohol with a Single-Site Homogeneous Ti-Si Epoxidation Catalyst: A Spectroscopic and Computational Study

Urakawa, Atsushi
Skrabal, Peter
Bangerter, Felix
Baiker, Alfons
Published in Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical. 2005, vol. 109, no. 6, p. 2212-2221
Abstract Tetrakis(trimethylsiloxy)titanium (TTMST, Ti(OSiMe3)4) possesses an isolated Ti center and is a highly active homogeneous catalyst in epoxidation of various olefins. The structure of TTMST resembles that of the active sites in some heterogeneous Ti−Si epoxidation catalysts, especially silylated titania−silica mixed oxides. Water cleaves the Ti−O−Si bond and deactivates the catalyst. An alkyl hydroperoxide, TBHP (tert-butyl hydroperoxide), does not cleave the Ti−O−Si bond, but interacts via weak hydrogen-bonding as supported by NMR, DOSY, IR, and computational studies. ATR−IR spectroscopy combined with computational investigations shows that more than one, that is, up to four, TBHP can undergo hydrogen-bonding with TTMST, leading to the activation of the O−O bond of TBHP. The greater the number of TBHP molecules that form hydrogen bonds to TTMST, the more electrophilic the O−O bond becomes, and the more active the complex is for epoxidation. An allylic alcohol, 2-cyclohexen-1-ol, does not interact strongly with TTMST, but the interaction is prominent when it interacts with the TTMST−TBHP complex. On the basis of the experimental and theoretical findings, a hydrogen-bond-assisted epoxidation mechanism of TTMST is suggested.
Stable URL https://archive-ouverte.unige.ch/unige:14730
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Other version: http://pubs.acs.org/doi/pdf/10.1021/jp048999q

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Deposited on : 2011-03-18

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