Copper-Coordinated Histidyl Bolaamphiphile Assembly as an Oxidative Catalyst: Coordination Structure and Catalytic Activity in Cyclohexane Oxidation

Surface-exposed imidazole moieties of a supramolecular self-assembly of histidyl bolaamphiphile (HisC7) readily coordinate at transition metal ions. In this study, the Cu-coordinated histidyl bolaamphiphile assembly (HisC7[Cu]) is demonstrated to be an effective oxidative catalyst, with a Fenton-active copper center. HisC7[Cu] catalytically oxidized cyclohexane to produce cyclohexanol in the yield of 20.2 %, which is comparable to other homogeneous catalysts. The coordination sphere of the active copper center is investigated through various spectroscopic techniques in consideration of the catalytic activity. The highest catalytic activity is exhibited by the HisC7[Cu] catalyst prepared at a HisC7/Cu molar ratio of 0.75, where the copper center of HisC7[Cu] has a 1N3O coordination environment. The copper center with bidentate coordination to imidazole groups shows low activity due to the lack of open coordination sites. The HisC7[Cu] catalyst is applied to the oxidation of cyclohexane, and the reaction characteristics and reusability of HisC7[Cu] are studied.