[Bis(catechol)salen]MnIII coordination polymers as support-free heterogeneous asymmetric catalysts for epoxidation

The formation of coordination polymers by the reaction of [bis(catechol)salen]Mn-III with several di- and trivalent metal ions is reported. These polymers are insoluble in a wide range of organic solvents and water but can be dissolved upon addition of excess pyrocatechol. They function as enantioselective heterogeneous epoxidation catalysts and exhibit catalytic activity comparable to that of the homogeneous [bis(catechol)salen]Mn-III building block alone when used for the enantioselective epoxidation of 2,2-dimethyl-2H-chromene. After catalysis, catalyst isolation from the reaction mixture can be readily achieved by centrifugation and decantation. Under practical oxidant concentrations, the catalyst can be recycled up to ten times with little loss of activity and no loss of enantioselectivity. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).