TY - JOUR AU - Urakawa, Atsushi AU - Bürgi, Thomas AU - Skrabal, Peter AU - Bangerter, Felix AU - Baiker, Alfons TI - Interaction of Water, Alkyl Hydroperoxide, and Allylic Alcohol with a Single-Site Homogeneous Ti-Si Epoxidation Catalyst: A Spectroscopic and Computational Study PY - 2005 JF - Journal of Physical Chemistry B JA - J. Phys. Chem. B SN - 1520-6106 VL - 109 IS - 6 SP - 2212 EP - 2221 L1 - http://pubs.acs.org/doi/pdf/10.1021/jp048999q L2 - http://pubs.acs.org/doi/full/10.1021/jp048999q L3 - http://pubs.acs.org/doi/abs/10.1021/jp048999q M3 - 10.1021/jp048999q UR - http://dx.doi.org/10.1021/jp048999q N2 - 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. ID - 1103 ER -