| An Fe(III)-NO-bound model compound, [Fe(III)S2Me2N 3(Pr,Pr)(NO)]PF6 (1-NO), is prepared. Its electronic properties are nearly identical to those of the active site in NO-inactivated NHase. Therefore, the assignment of the active site in NO inactivated NHase as being {FeNO}6 is supported. The stability of 1-NO demonstrates that the 'claw' structure observed in NHase is not necessary to stabilize an Fe(III)-NO species.;To examine how small structural changes influence the reactivity of metal complexes, a series of related Fe(III) thiolate complexes was synthesized and characterized. A hexacoordinated Fe(III) complex containing an eta 2-coordinated persulfide is described, [Fe(III)(S2 Me2N3(Et,Pr))-Spers]PF6 ( 4). It is the first structurally characterized, first row transition metal-eta2-persulfide complex. This complex is a model for the possible interaction between cysteine persulfide (thiocysteine, cysteine perthiolate) and Fe(III) in biological systems. The extra persulfide sulfur can be removed to afford a pentacoordinated compound, [Fe(III)S2 Me2N3(Et,Pr)]PF6 (5), which possesses a more open binding site than the previously reported, pentacoordinated model compound [Fe(III)S2Me2N3(Pr,Pr)]PF 6 (1). A comparison of the reaction of 1 and 5 with azide provides a model system for the concept of entatic state.;Further, the Fe(III) coordination chemistry of N,N'-1,2-ethanediylbis[2-mercapto-2-methyl-propanamide] was investigated. Thereby, two compounds, (NMe4)2[(Fe(III)S 2Me2N2amide(Et))2] (6) and (NMe4)[Fe(III)S2Me2N 2amide(Et)(Py)] (7), were isolated that contain deprotonated carboxamide nitrogens coordinated to Fe(III). The deprotonated carboxamide nitrogens provide significant stabilization to the +3 oxidation state of the Fe(III) ion, as indicated by the reduction potential. A comparison of pentacoordinated, carboxamide nitrogencoordinated 7 with another pentacoordinated, imine nitrogen-coordinated model compound provides evidence that an imine group is a valid structural and electronic model for a carboxamide. |
