Iron Nitrosyls of a Pentadentate Ligand Containing a Single Carboxamide Group:  Syntheses, Structures, Electronic Properties, and Photolability of NO

Abstract

Three iron complexes of a pentadentate ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy(3)H, H is the dissociable amide proton) have been synthesized. All three species, namely, two nitrosyls [(PaPy(3))Fe(NO)](ClO(4))(2) (2) and [(PaPy(3))Fe(NO)](ClO(4)) (3) and one nitro complex [(PaPy(3))Fe(NO(2))](ClO(4)) (4), have been structurally characterized. These complexes provide the opportunity to compare the structural and spectral properties of a set of isostructural [Fe-NO](6,7) complexes (2 and 3, respectively) and an analogous genuine Fe(III) complex with an "innocent" sixth ligand ([(PaPy(3))Fe(NO(2))](ClO(4)), 4). The most striking difference in the structural features of 2 and 3 is the Fe-N-O angle (Fe-N-O = 173.1(2) degrees in the case of 2 and 141.29(15) degrees in the case of 3). The clean (1)H NMR spectrum of 2 in CD(3)CN reveals its S = 0 ground state and confirms its [Fe-NO](6) configuration. The binding of NO at the non-heme iron center in 2 is completely reversible and the bound NO is photolabile. Mössbauer data, electron paramagnetic resonance signal at g approximately 2.00, and variable temperature magnetic susceptibility measurements indicate the S = (1)/(2) spin state of the [Fe-NO](7) complex 3. Analysis of the spectroscopic data suggests Fe(II)-NO(+) and Fe(II)-NO(*) formulations for 2 and 3, respectively. The bound NO in 3 does not show any photolability. However, in MeCN solution, it reacts rapidly with dioxygen to afford the nitro complex 4, which has also been synthesized independently from [(PaPy(3))Fe(MeCN)](2+) and NO(2)(-). Nucleophilic attack of hydroxide ion to the N atom of the NO ligand in 2 in MeCN in the dark gives rise to 4 in high yield.

Iron(III) Complexes with the Ligand N′,N′‐Bis[(2‐pyridyl)methyl]ethylenediamine (uns‐penp) and Its Amide Derivative N‐Acetyl‐N′,N′‐bis[(2‐pyridyl)methyl]ethylenediamine (acetyl‐uns‐penp)

“…[18,[27][28][29][30][31][32][33][76][77][78] A copper() complex was recently reported, where the carboxamido function of acetyl-uns-penp is no longer truly sp 2 hybridised and the nitrogen atom undergoes a weak interaction with the metal centre. [13] In our present work, we demonstrated that acetyl-uns-penp is capable of influencing coordination chemistry by building hydrogen bonds with hydrogen acceptors in the vicinity of the carboxamido function.…”

New precursor for the post-synthesis preparation of Fe-ZSM-5 zeolites with low iron content

“…[8]. This method lead, in our lab, to better results (in terms of [15,[30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] for Fe 3+ (NO) complexes; Refs. [15,17,18,35,[47][48][49][50][51][52] for Fe 2+ (NO); Refs.…”

Photo-Controlled Release of NO and CO with Inorganic and Organometallic Complexes

“…In 2002, Patra, Mascharak and co-workers reported the NO photo-releasing properties of iron nitrosyl complexes with several carboxamide-containing pentadentate ligands [50,81].…”

“…However, the stability of this complex in biological media is poor [81,82]. From DFT calculations, it was observed that the electronic transition that labilizes NO occurs from a bonding Fe-NO orbital with a partial carboxamide character to an antibonding Fe-NO orbital.…”