Biomimetic interaction between Fe(II) and O2: effect of the second coordination sphere on O2 binding to Fe(II) complexes: evidence of coordination at the metal centre by a dissociative mechanism in the formation of mu-oxo diferric complexes.
We report that the formation of mu-oxo diferric compounds from O(2) and FeCl(2) complexes within the tris(2-pyridylmethyl)amine series (N. K. Thallaj et al. Chem. Eur. J., 2008, 14, 6742-6753) involves coordination of O(2) to the metal centre and that this reaction occurs following initial dissociation of the bound equatorial chloride anion. We also report evidence of the formation of a reduced form of dioxygen by an inner-sphere mechanism, thus leading to modification of the ligand. The solid-state structures of [FeCl(2)L] complexes (L(1) = mono(alpha-pivalamidopyridylmethyl)bis(2-pyridylmethyl)amine, L(2) = mono(alpha-pivalesteropyridylmethyl)bis(2-pyridylmethyl)amine, L(3) = bis(alpha-pivalamidopyridylmethyl)mono(2-pyridylmethyl)amine are described, and spectroscopic data support the structural retention in solution. In [FeCl(2)L(3)], the two amide hydrogen atoms stabilise the equatorial chloride anion in such a way that its exchange by a weak ligand is impossible: [FeCl(2)L(3)] is perfectly oxygen-stable. In [FeCl(2)L(2)], the equatorial chloride anion is completely free to move and coordination of O(2) can take place. The reaction product with [FeCl(2)L(2)] is a mu-oxo diferric complex in which the ester function has been transformed into a phenol group. This conversion can be seen as a hydrolysis reaction in basic medium, hence supporting the initial formation of a reduced form of dioxygen in the medium. Complex [FeCl(2)L(1)] exhibits a very weak reactivity with O(2), in line with a semistabilised equatorial chloride counteranion.
Wane
Amadou
A
Laboratoire de Chimie Biomimétique des Métaux de Transition, Institut de Chimie, UMR CNRS no. 7177, Université de Strasbourg, 4 rue Blaise Pascal, B.P. 1032, 67070 Strasbourg cedex, France.
Thallaj
Nasser K
NK
Mandon
Dominique
D
D005296:Ferrous Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*
D005296:Ferrous Compounds; D011725:Pyridines; C431843:tris(2-pyridylmethyl)amine; D010100:Oxygen