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 alumosilicate Ti-ITQ-2

Abstract A comparative study of silane oxidation, olefin epoxidation, and thianthrene 5-oxide sulfoxidation with the oxidants Ti-β/H 2 O 2 , 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(O i -Pr) 4 / t -BuOOH oxidant.