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Switching on oxygen activation by cobalt complexes of pentadentate ligands

Artikel i vetenskaplig tidskrift
Författare Mads S. Vad
Anne Nielsen
Anders Lennartson
Andrew D. Bond
John E. McGrady
Christine J. McKenzie
Publicerad i Dalton Transactions
Volym 40
Sidor 10698-10707
ISSN 14779226
Publiceringsår 2011
Publicerad vid
Sidor 10698-10707
Språk en
Ämneskategorier Kemi

Sammanfattning

The monoanionic N 4 O ligand N-methyl-N,N′-bis(2- pyridylmethyl)ethylenediamine-N′-acetate (mebpena - ) undergoes oxidative C-N bond cleavage in the presence of Co(ii) and O 2 . The two resultant fragments are coordinated to the metal ion in the product [Co III (2-pyridylformate)(mepena)]ClO 4 (mepena - = N-methyl-N′-(2-pyridylmethyl)ethylenediamine-N′-acetato). Bond cleavage does not occur in the presence of chloride ions and [Co III (mebpena)Cl] + , containing intact mebpena - , can be isolated. The oxidative instability of the mebpena - in the presence of Co(ii) and air stands in contrast to the oxidative stability of the family of very closely related penta- and hexa-dentate ligands in their cobalt complexes. Cyclic voltammetry on the matched pair [Co III Cl(mebpena)] + and [Co II Cl(bztpen)] + , bztpen = N-benzyl-N,N′,N′-tris(2-pyridylmethyl)ethylenediamine, shows that substitution of a pyridine donor for a carboxylato donor results in a relatively small cathodic shift of 150 mV in the E°(Co(ii)/Co(iii)) oxidation potential, presumably this is enough to determine the contrasting metal oxidation state in the complexes isolated under ambient conditions. DFT calculations support a proposal that [Co II (mebpena)] + reacts with O 2 to form a Co(iii)-superoxide complex which can abstract an H atom from a ligand methylene C atom as the initial step towards the observed oxidative C-N bond cleavage. © 2011 The Royal Society of Chemistry.

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