Twenty-two Mn-II complexes were screened for the catalytic epoxidation of terminal olefins using peracetic acid as the oxidant. A limited number of these complexes are efficient catalysts using peracetic acid solutions generated with H2SO4 (PAAc), but most complexes are effective at 1 mol% catalyst loading using peracetic acid generated with strongly acidic resins (PAAR). Under the less acidic conditions of PAAR, [Mn-II(phen)(2)(CF3SO3)(2)] has the highest activity of the catalysts screened, and epoxides terminal olefins using as little as 0.02 mol% catalyst within 5 min. The dimeric species [Mn-2(III.IV)(phen)(4)(O)(2)](ClO4)(3) is also a viable epoxidation catalyst with PAAR, but the dimeric species is reduced by the residual H2O, to monomeric Mu(II) species under the reaction conditions. By comparison, a similar dimeric complex [Mn-2(III,IV)(R,R-MCP)(2)(O)(2)](ClO4)(3), is not reduced by H,O, under the reaction conditions and is not catalytically active, supportive of the notion that the catalytically relevant species is monomeric. (c) 2006 Elsevier B.V. All rights reserved.