Mechanistic Information on the Reversible Binding of NO to Mono‐ and Dinuclear FeII Complexes of a Biomimetic S4N Ligand

Abstract

AbstractStructural and mechanistic information on the binding of NO to mono‐ and dinuclear [FeII(S4NNEt2)] fragments as potential catalysts for the removal of NO from effluent gas streams have been obtained from concentration, temperature and pressure dependent kinetic measurements using stopped‐flow techniques. The results indicate that the steric and electronic structure only affect the rate but not the nature of the binding mechanism by which NO coordinates to the selected complexes. Therefore, the sterically hindered dinuclear complex [FeII(S4NNEt2)]2 binds NO ca. eight times slower than the corresponding mononuclear complex [FeII(CH3OH)(S4NNEt2)]. Significantly negative ΔS# values were found for the binding of NO to both the mono‐ and dinuclear species, and are consistent with an associative mechanism. The negative volumes of activation observed for the binding of NO to both dinuclear [FeII(S4NNEt2)]2 and mononuclear [FeII(CO)(S4NNEt2)] complexes further supports the operation of an associative mechanism. Structural studies on the [FeII(NO)(S4NNEt2)] complex indicate it to be six‐coordinate, low‐spin iron(II) with a neutral NO ligand.