Titanium-Catalyzed Heterogeneous Oxidations of Silanes, Chiral Allylic Alcohols, 3-Alkylcyclohexanes, and Thianthrene 5-Oxide: A Comparison of the Reactivities and Selectivities for the Large-Pore Zeolite Ti-β, the Mesoporous Ti-MCM-41, and the Layered Al

A comparative study of silane oxidation, olefin epoxidation, and thianthrene 5-oxide sulfoxidation with the oxidants Ti-β/H2O2, Ti-MCM-41/t-BuOOH, and Ti-ITQ-2/t-BuOOH provides the catalytic reactivity order Ti-β>Ti-MCM-41>Ti-ITQ-2. The steric constraints of the narrow channels make the Ti-β zeolite the most selective. For the more open structures of the Ti-MCM-41 and Ti-ITQ-2 hosts, such steric constraints are less pronounced and, therefore, a lower selectivity is exhibited by these heterogeneous catalysts. Both activate t-BuOOH for oxygen transfer through a transition structure analogous to the homogeneous Ti(Oi-Pr)4/t-BuOOH oxidant.