| Abstract
| - Tetrakis(trimethylsiloxy)titanium (TTMST, Ti(OSiMe3)4) possesses an isolated Ti center and is a highly activehomogeneous catalyst in epoxidation of various olefins. The structure of TTMST resembles that of the activesites 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-butylhydroperoxide), does not cleave the Ti−O−Si bond, but interacts via weak hydrogen-bonding as supportedby NMR, DOSY, IR, and computational studies. ATR−IR spectroscopy combined with computationalinvestigations 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 formhydrogen bonds to TTMST, the more electrophilic the O−O bond becomes, and the more active the complexis for epoxidation. An allylic alcohol, 2-cyclohexen-1-ol, does not interact strongly with TTMST, but theinteraction is prominent when it interacts with the TTMST−TBHP complex. On the basis of the experimentaland theoretical findings, a hydrogen-bond-assisted epoxidation mechanism of TTMST is suggested.
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