Department of Chemical and Biomolecular Engineering , University of California, Berkeley , Berkeley , California 94720 , United States.
Institut für Physikalische Chemie , Westfälische Wilhelms-Universität Münster , Münster 48149 , Germany.
J Am Chem Soc. 2018 Apr 18;140(15):4956-4960. doi: 10.1021/jacs.7b11467. Epub 2018 Apr 3.
The effect of outer-sphere environment on alkene epoxidation catalysis using an organic hydroperoxide oxidant is demonstrated for calix[4]arene-Ti single-sites grafted on amorphous vs crystalline delaminated zeotype (UCB-4) silicates as supports. A chelating calix[4]arene macrocyclic ligand helps enforce a constant Ti inner-sphere, as characterized by UV-visible and X-ray absorption spectroscopies, thus enabling the rigorous comparison of outer-sphere environments across different siliceous supports. These outer-sphere environments are characterized by solid-state H NMR spectroscopy to comprise proximally organized silanols confined within 12 membered-ring cups in crystalline UCB-4, and are responsible for up to 5-fold enhancements in rates of epoxidation by Ti centers.
采用有机过氧化物氧化剂，通过杯[4]芳烃钛单分子在无定形与层状剥落沸石型（UCB-4）硅酸盐上的负载，展示了外部环境对烯烃环氧化催化作用的影响。螯合杯[4]芳烃大环配体有助于保持 Ti 的内配位环境不变，这可以通过紫外可见和 X 射线吸收光谱来证明，从而可以严格比较不同硅质载体的外部环境。这些外部环境通过固态 H NMR 光谱来进行表征，包含在结晶 UCB-4 的 12 元环杯中被紧密组织的硅醇，并且负责提高钛中心的环氧化反应速率高达 5 倍。
