Monomeric and dimeric complexes of Mn 1,4,7-trimethyl-1,4,7-triazacyclononane (tmtacn) were immobilized under reaction conditions onto solid supports to create heterogeneous catalysts for epoxidation with H2O2. These solid supports consist of activated carbon or silica grafted or co-condensed with benzoic or C3/C4 acids that function both as tethering points and as required co-catalysts. Immobilized catalysts were as much as 50-fold faster than the analogous soluble system, and an immobilized, dimeric Mn(tmtacn) complex with a solid benzoic acid co-catalyst gave the highest yields to epoxide. A Hammett study on the catalytic epoxidation of a series of styrenes showed weak increases in yield for more electron-withdrawing p-substituents reactants for both immobilized complexes, which runs counter to previous observations with analogous homogeneous catalysts, and which appears to reflect a previously unappreciated tradeoff between the intrinsic epoxidation reactivity and strong catalyst inhibition by styrene oxides and glycols. Finally, these catalysts were tested with a variety of solid-co-catalysts, and were successfully utilized in the challenging epoxidation of divinylbenzene to industrially-useful divinylbenzene dioxide using a cascade of two catalyst charges.
Bibliographical noteFunding Information:
The authors acknowledge financial assistance from The Dow Chemical Company and thank Dr. Kurt Hirsekorn and Dr. Nicholas Schoenfeldt for helpful discussions. A.B.T. also acknowledges financial support from NSF grant CBET-0933667. SS 13 C CP/MAS NMR spectroscopy was performed at IMSERC, funded by NSF DMR-0521267. SEM and DRIFTS experiments were carried out at NUANCE with support from NSF-NSEC, NSF-MRSEC, Keck Foundation, the State of Illinois and Northwestern University.
© 2015 Elsevier B.V.
Copyright 2015 Elsevier B.V., All rights reserved.
- Hammett relationships
- Hydrogen peroxide
- Supported catalyst