Reactions of [H4L][PF6]4 with 4 equiv. of Mn(OAc)2·4H2O in the presence of air gave rise to a mononuclear Mn(III)–superoxo complex [Mn(III)L(O2)(H2O)](PF6)2, which contains a bowl-shaped cationic structure with a D4d symmetry. It has an unprecedented linear end-on Mn(III)–O2 unit and exhibited good efficiency and selectivity in the catalytic oxidation of alkenes with O2 plus isobutyraldehyde under mild conditions.
![Graphical abstract: A Mn(iii)–superoxo complex of a zwitterionic calix[4]arene with an unprecedented linear end-on Mn(iii)–O2 arrangement and good catalytic performance for alkene epoxidation](http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=C1CC14262C "Graphical abstract")