Catalyst structure and substituent effects on epoxidation of styrenics with immobilized Mn(tmtacn) complexes

•Monomeric and dimeric manganese triazacyclononane complexes are immobilized onto, and activated by, solid carboxylates.•Styrene epoxidation rates and yields depend on complex nuclearity and support, and can be 50-fold that of the homogeneous complex.•Yields increase for e-withdrawing substituents, up to 100% yield and 1000 TON for cyanostyrene. This trend is counter to expectations and reflects inhibition by minor, ring-opening side products.•Optimizing conditions allows up to 75% yield of challenging bis-epoxides from divinylbenzene.

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.

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