from first principles PP-I-1

KL-9Active Species of Nonheme Iron- and Manganese-Catalyzed OxidationBryliakov K.P. 1 , Lyakin O.Y. 1 , Ottenbacher R.V. 1,2 , Talsi E.P. 11 Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia2 Novosibirsk State University, Novosibirsk, Russiatalsi@catalysis.ruWithin biomimetic oxidation catalysts, aminopyridine complexes of such biologicallyimportant elements as Fe and Mn attract particular attention. [1] These complexes have beenfound to efficiently catalyze olefin epoxidation with percarboxylic acids or H 2 O 2 /AcOH in achemo- and sometimes enantioselective fashion. [1,2] Electron paramagnetic resonance (EPR)spectroscopy has been used to characterize oxidizing species in the catalyst systems 1-4/H 2 O 2 .It was found that very unstable intermediates 1c-4c exhibiting similar rhombic S = 1/2 EPRsignals and active towards epoxidation of olefins are formed in these systems. [3] Costas,Cronin, and co-workers have used cryospray-assisted variable temperature mass spectrometry(VT-MS), to detect an elusive HO–Fe V =O intermediate in the catalyst system 4/H 2 O 2 . [4]Direct correlation of VT-MS and EPR data shows that S = 1/2 intermediate 4c wellcorresponds to the oxoiron(V) species identified in the same system by VT-MS. Apparently,complexes 1c-4c are similar oxoiron(V) species. Comparative studies of asymmetric olefinepoxidation by Fe and Mn catalyst systems 3/H 2 O 2 /RCOOH and 5/H 2 O 2 /RCOOH haveshown that 3 and 5 conduct enantioselective epoxidation of prochiral olefins with H 2 O 2 in thepresence of carboxylic acids, manganese catalyst 5 demonstrating much higher efficiency(1000 vs. 100 TON) and enantioselectivity (up to 93% ee: the highest value ever reported foraminopyridine manganese catalysts). The enantioselectivity drastically increases with risingsteric bulk of the acid, thus indicating the presence of the carboxylic moiety in the activespecies. On the basis of EPR and enantioselectivity data, the active species can be assigned tocomplexes [LM V =O(OC(O)R] 2+ (where M = Fe or Mn, R = alkyl, L = aminopyridine ligand).NNOTfOTfNNNOTfIIFeOTfNNNNII NCCH 3 N II NCCH 3* N IIFeFe (S,S)- FeNCCH 3N* NNCCHN3NN(ClO 4 ) 2 (ClO4 ) 2*(S,S)-*NNNII MnNOTfOTf12References:[1] L. Que, Jr., W.B. Tolman, Nature 455 (2008) 333.[2] M. Wu, B. Wang, S. Wang, C. Xia, W. Sun, Org. Lett. 11 (2009) 3622. R.V. Ottenbacher, K.P.Bryliakov, E.P. Talsi, Adv. Synth. Catal. 353 (2011) 885.[3] O.Y. Lyakin, K.P. Bryliakov, G.J.P. Britovsek, E.P. Talsi, J. Am. Chem. Soc. 131 (2009) 10798.[4] I. Prat, J.S. Mathieson, L. Cronin, M. Costas et al., Nat. Chem. 3 (2011) 788.26345