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Issue 21, 2011
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The radical mechanism of cobalt(II) porphyrin-catalyzed olefin aziridination and the importance of cooperative H-bonding

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Abstract

The mechanism of cobalt(II) porphyrin-mediated aziridination of styrene with PhSO2N3 was studied by means of DFT calculations. The computations clearly indicate the involvement of a cobalt ‘nitrene radical’ intermediate in the CoII(por)-catalyzed alkene aziridination. The addition of styrene to this species proceeds in a stepwise fashion via radical addition of the ‘nitrene radical’ C to the C[double bond, length as m-dash]C double bond of styrene to form a γ-alkyl radical intermediate D. The thus formed tri-radical species D easily collapses in an almost barrierless ring closure reaction (TS3) to form the aziridine, thereby regenerating the cobalt(II) porphyrin catalyst. The radical addition of the ‘nitrene radical’ C to the olefin (TS2) proceeds with a comparable barrier as its formation (TS1), thus providing a good explanation for the first order kinetics in both substrates and the catalyst observed experimentally. Formation of C is clearly accelerated by stabilization of C and TS1viahydrogen bonding between the S[double bond, length as m-dash]O and N–H units. The computed radical-type mechanism agrees well with all available mechanistic and kinetic information. The computed free energy profile readily explains the superior performance of the CoII(porAmide) system with H-bond donor functionalities over the non-functionalized Co(TPP).

Graphical abstract: The radical mechanism of cobalt(ii) porphyrin-catalyzed olefin aziridination and the importance of cooperative H-bonding

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Publication details

The article was received on 07 Jan 2011, accepted on 17 Mar 2011 and first published on 11 Apr 2011


Article type: Paper
DOI: 10.1039/C1DT10027K
Citation: Dalton Trans., 2011,40, 5697-5705
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    The radical mechanism of cobalt(II) porphyrin-catalyzed olefin aziridination and the importance of cooperative H-bonding

    A. I. Olivos Suarez, H. Jiang, X. P. Zhang and B. de Bruin, Dalton Trans., 2011, 40, 5697
    DOI: 10.1039/C1DT10027K

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