Formation of a triply bridged µ-oxo diiron(iii) core stabilized by two deprotonated carboxamide groups upon photorelease of NO from a {Fe–NO}6 iron nitrosyl

Abstract

The iron nitrosyl [(PaPy2Q)Fe(NO)](ClO4)2 (2), derived from the quinoline-based ligand PaPy2QH (N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-quinoline-2-carboxamide, where H is dissociable proton) has been characterized by spectroscopy and X-ray diffraction techniques. The 1H NMR spectrum (S = 0 ground state) and v(NO) value of 1885 cm(-1) indicate that 2 is a [Fe-NO]6 nitrosyl. Although 2 is stable in the dark, exposure of an acetonitrile solution of 2 (lambdamax = 510 nm) to light in the visible range causes rapid release of NO and formation of the solvato species [(PaPy2Q)Fe(MeCN)](ClO4)2 (6). Quantum yield (Phi) measurements indicate that 2 is a more efficient NO donor (Phi = 0.258) than [(PaPy3)Fe(NO)](ClO4)2 (1, Phi = 0.185), a complex derived from a similar but pyridine-based ligand. Interestingly, when the photoproduct 6 is exposed to water or a small amount of base, the triply bridged diiron(III) species [(PaPy2Q)FeOFe(PaPy2Q)](ClO4)2 (3) forms in good yield. This species can be independently synthesized from aerobic oxidation of the Fe(II) species [(PaPy2Q)Fe(MeCN)](ClO4) in acetonitrile. The structure of 3 reveals a unique Fe(III)-O-Fe(III) link supported by two (eta2,mu2)mu-NCO bridges derived from the carboxamido groups of the two (PaPy2Q)Fe(III) moieties.

Syntheses, Structures, and Photochemistry of Manganese Nitrosyls Derived from Designed Schiff Base Ligands: Potential NO Donors That Can Be Activated by Near-Infrared Light

“…18 This diamagnetic non-heme nitrosyl rapidly releases NO upon illumination with 5-10 mW of visible light (500-600 nm) in solvents such as acetonitrile (Φ = 0.18). 20 The corresponding {Ru-NO} 6 nitrosyl [Ru(PaPy 3 )(NO)](BF 4 ) 2 exhibits NO photolability under UV illumination. 21 We have also synthesized a series of {Ru-NO} 6 nitrosyls coordinated to tetradentate planar dicarboxamide N 4 ligands that also release NO upon exposure to light in the range 320-500 nm.…”

Synthesis of N-Pyridin-2-ylmethyl and N-Quinolin-2-ylmethyl ­Substituted Ethane-1,2-diamines

“…This complex can readily release NO upon illumination by near-infrared (NIR) light of low intensity (<5 mW, 780 nm). 29 A similar redshift was also observed for 1,2-bis(quinaldine-2-carboxamido)-4,5-dimethylbenzene (H 2 Me 2 bqb), in which a pyridine-2-carboxylic acid moiety was replaced with a quinolyl-2-carboxic acid group. 26,30 In an effort to develop effective NO donors for the treatment of prostate cancer, we selected (PaPy 2 QH) as the base structure and added moieties that can enable incorporation onto carboxylic group-containing gold-nanoparticles whose surfaces would be further modified with prostatespecific membrane antigens (PSMA-a10) for targeted delivery.…”

“…According to the published results for PaPy 2 QH, compounds 11, 18, 12, and 19 formed complexes with Mn(II)-NO likely release NO by NIR light at or above 780 nm wavelength illumination. 29 The chemistry used for the preparation of the 6-aminoethoxy substituted quinoline-2-carboximide analogues is shown in Scheme 1. Both 11 and 12 were synthesized in 10 steps from the starting material 6-methoxyquinoline.…”

“…25,26 One compound with the structure of N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy 3 H) has been identified as an effective complexing agent for several metal ions, such as Mn(II), Mn(III), Fe(III), and Ru(III). [27][28][29] On replacing the pyridyl-2-carboxamide moiety in PaPy 3 H with a quinolyl-carboxamide structure, the resultant compound, N,N-bis (2-pyridylmethyl)amine-N-ethyl-2-quinoline-2-carboxamide (PaPy 2 QH), has a significant redshift on forming the manganese nitrosyl complex due to additional conjugation ( Figure 1). This complex can readily release NO upon illumination by near-infrared (NIR) light of low intensity (<5 mW, 780 nm).…”

Crystal structure of 1,1′-(pyridine-2,6-diyl)bis[N-(pyridin-2-ylmethyl)methanaminium] dichloride dihydrate

“…The utilization of polydentate ligands in coordination chemistry gives a few benefits over monodentate ligands, in particular because of the chelate effect (Martell, 1967). Multidentate pyridylamine derivative ligands can better control the stability (Afshar et al, 2004;Eroy-Reveles et al, 2007), solubility (Harrop et al, 2005) and structural characteristics of the resulting complex. More particularly, ruthenium complexes derived from pentadentate ligands are generally stable in physiological media (Halpenny et al, 2007;Rose & Mascharak, 2008b).…”