Syntheses, structures, and reactivities of {Fe-NO}6 nitrosyls derived from polypyridine-carboxamide ligands:: Photoactive NO-donors and reagents for S-nitrosylation of alkyl thiols

Two new iron nitrosyls derived from two designed pentadentate ligands N,N-bis(2-pyridylmethyl)-amine-N'-(2-pyridylmethyl)acetamide and N,N-bis(2-pyridylmethyl)-amine-N'-[1-(2-pyridinyl)ethyl]acetamide (PcPy3H and MePcPy3H, respectively, where H is the dissociable amide proton) have been structurally characterized. These complexes are similar to a previously reported {Fe-NO}(6) Complex, [(PaPy3)Fe(NO)](ClO4)(2) (1) that releases NO under mild conditions. The present nitrosyls, namely [(PcPy3)Fe(NO)](ClO4)(2) (2) and [(MePcPy3)Fe(NO)](ClO4)(2) (3), belong to the same {Fe-NO}(6) family and exhibit (a) clean H-1 NMR spectra in CD3CN indicating S = O ground state, (b) almost linear Fe-N-O angles (177.3(5)degrees and 177.6(4)degrees for 2 and 3, respectively), and (c) N-O stretching frequencies (v(NO)) in the range 1900-1925 cm(-1). The binding of NO at the non-heme iron centers of 1-3 is completely reversible and all three nitrosyls rapidly release NO when exposed to light (50 W tungsten bulb). In addition to acting as photoactive NO-donors, these complexes also nitrosylate thiols such as N-acetylpenicillamine, 3-mercaptopropionic acid, and N-acetyl-cysteine-methyl-ester in yields that range from 30 to 90% in the absence of light. The addition of alkyl or aryl thiolate (RS-) to the {Fe-NO}(6) Complexes in the absence of dioxygen results in the reduction of the iron metal center to afford the corresponding {Fe-NO}(7) species.