The manganese(V) oxo complex (TBP(8)Cz)Mn-V(O) (1) is shown to catalyze the epoxidation of alkenes with a series of iodosylarenes (ArlO) as oxidants. Competition experiments reveal that the identity of ArlO influences the product ratios, implicating an unusual coordinated oxo metal ArlO intermediate (1-OIAr) as the active catalytic species. The isoelectronic manganese(V) imido complex (TBP(8)Cz)Mn-V(NMes) (2) does not participate in NR transfer but does catalyze epoxidations with ArlO as the O-atom source, suggesting a mechanism similar to that seen for 1. Direct evidence (ESIMS) is obtained for 1-OIMes.