Outer-Sphere Control of Catalysis on Surfaces: A Comparative Study of Ti(IV) Single-Sites Grafted on Amorphous versus Crystalline Silicates for Alkene Epoxidation

• Published in: Journal of the American Chemical Society Vol. 140; no. 15; pp. 4956 - 4960
• Main Authors: Grosso-Giordano, Nicolás A, Schroeder, Christian, Okrut, Alexander, Solovyov, Andrew, Schöttle, Christian, Chassé, Walter, Marinković, Nebojša, Koller, Hubert, Zones, Stacey I, Katz, Alexander
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 18.04.2018; American Chemical Society (ACS)
• Subjects: Chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.7b11467

The effect of outer-sphere environment on alkene epoxidation catalysis using an organic hydroperoxide oxidant is demonstrated for calix[4]­arene-TiIV 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 TiIV 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 1H 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 TiIV centers.