Phosphine-ligated dinitrosyl iron complexes for redox-controlled NO release

Abstract

Here we present the syntheses and structural, spectroscopic, as well as electrochemical properties of four dinitrosyl iron complexes (DNICs) based on silicon- and carbon-derived di- and tripodal phosphines. Whereas CH₃C(CH₂PPh₂)₃ and Ph₂Si(CH₂PPh₂)₂ coordinate iron in a η² – binding mode, CH₃Si(CH₂PPh₂)₃ undergoes cleavage of one Si–C bond to afford [Fe(NO)₂(P(CH₃)Ph₂)₂] at elevated temperatures. The complexes were characterized by IR spectroelectrochemistry as well as UV-vis measurements. The oxidized {Fe(NO)₂}⁹ compounds were obtained by oxidation with (NH₄)₂[Ce(NO₃)₆] and their properties evaluated with Mössbauer and IR spectroscopy. Stability experiments on the complexes suggest that they are capable of releasing their NO-ligands in the oxidized {Fe(NO)₂}⁹ but not in the reduced {Fe(NO)₂}¹⁰ form. A detailed DFT analysis is provided in order to understand the electronic configurations and the complexes’ ability to release NO.