from first principles PP-I-1

OY-II-2Non-Heme Iron and Manganese-Catalyzed Asymmetric OlefinEpoxidations with H 2 O 2 : Probing the Nature of Active Species by EPRSpectroscopic and Enantioselectivity StudiesLyakin O.Y. 1 , Ottenbacher R.V. 1,2 , Bryliakov K.P. 1 , Talsi E.P. 11 Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia2 Novosibirsk State University, Novosibirsk, Russialyakin@catalysis.ruThe demand for efficient and sustainable regio- and stereoselective catalyst systems for theoxidation of organic substrates is continuously growing in line with toughening economic andenvironmental constraints. To date, Fe complexes with polydentate N-donor ligands areregarded as the best models of natural non-heme oxygenases capable of catalyzing selectiveoxidation of inactivated aliphatic C–H bonds with H 2 O 2 . [1] While the nature of active speciesin various non-heme iron/H 2 O 2 catalyst systems has been extensively studied in the last years,no mechanistic data have been reported for bipyrrolidine-based ((S,S)-pdp)Fe complexes ofthe type 1, that have been found to be remarkably efficient and selective catalysts of C–H[2, 3]oxidations and asymmetric cis-dihydroxylations. For1 (1.0 mol%) orrelated aminopyridine-basedmanganese systems, very little mechanistic data is available as yet.In this study, chiral bipyrrolidine-Nbased non-heme iron and manganeseR 3 2 (0.1 mol%)O R 3* N II OTf(S,S)- M*N OTfcomplexes 1 and 2 have been found to R 1 R 2 H 2 O 2 / RCOOHCHR 1 R 2N3 CN1 M = Fe2 M = Mncatalyze enantioselective epoxidationof prochiral olefins with H 2 O 2 in the presence of carboxylic acids, manganese catalyst 2demonstrating much higher efficiency (1000 vs. 100 TON) and enantioselectivity (up to 93%ee: the highest value ever reported for aminopyridine metal catalysts). The enantioselectivityrises with rising steric bulk of the acid, thus indicating the presence of the carboxylic moietyin the active species at the enantioselectivity-determining step. On the basis of EPR andenantioselectivity data, the active species can be assigned to [((S,S)-pdp)M V =O(OC(O)R)] 2+complexes (where M = Fe or Mn, R = alkyl). In the iron system, the correspondingintermediate [((S,S)-pdp)Fe V =O(OC(O)CH 3 )] 2+ has been trapped by EPR at −85 °C. Aconsistent mechanism for the active species formation is proposed.References:[1] L. Que, Jr., W.B. Tolman, Nature 455 (2008) 333.[2] M.S. Chen, M. C. White, Science 318 (2007) 783.[3] K. Suzuki, P.D. Oldenburg, L. Que, Jr., Angew. Chem., Int. Ed. 47 (2008) 1887.89