Can a Nitrosyl of a Mn(II)–Porphyrin Complex Release Nitroxyl/HNO?

Abstract

In general, the nitrosyl complexes of Mn(II)−porphyrinate having the {Mn(NO)} 6 configuration are not considered as HNO or nitroxyl (NO − ) donors because of [Mn I −NO + ] nature. A nitrosyl complex of Mn(II)− porphyrin, [Mn(TMPP 2− )(NO)], 1 [TMPPH 2 = 5,10,15,20-tetrakis-4-methoxyphenylporphyrin], is shown to release HNO in the presence of HBF 4 . It is evidenced from the characteristic reaction of HNO with triphenylphosphine and isolation of the [(TMPP 2− )Mn III (H 2 O) 2 ](BF 4 ), 2. This is attributed to the fact that H + from HBF 4 polarizes the NO group whereas the BF 4 − interacts with metal ion to stabilize the Mn(III) form. These two effects cooperatively result in the release of HNO from complex 1. In addition, complex 1 behaves as a nitroxyl (NO − ) donor in the presence of [Fe(dtc) 3 ] (dtc = diethyldithiocarbamate anion) and [Fe(TPP)(Cl)] (TPP = 5,10,15,20-tetraphenylporphyrinate) to result in [Fe(dtc) 2 (NO)] and [Fe(TPP)(NO)], respectively.

Sixth Ligand Induced HNO/NO– Release by a Five-Coordinated Cobalt(II) Nitrosyl Complex Having a {CoNO}8 Configuration

“…In the X-band EPR study of the reaction mixture at 77 K, the reaction mixture shows a sharp signal at g ∼ 2.04, which supports the formation of [Fe II (TPP)(NO)] in the reaction medium (Figure 3). 3,26,27 A similar reaction was observed with complex 1 in the presence of [Fe III (DTC) 3 ] without the addition of HBF 4 in a dry and degassed CH 2 Cl 2 medium. Upon addition, complex 1 was found to donate NO − to [Fe III (DTC) 3 ] to result in [Fe II (DTC) 2 (NO)].…”

“…This 1698 cm −1 stretching frequency is attributed to the nitrosyl stretching of newly formed [Fe II (TPP)-(NO)]. 3,14,26,27 The reaction was found to be completed in a near-quantitative manner. In the X-band EPR study of the reaction mixture at 77 K, the reaction mixture shows a sharp signal at g ∼ 2.04, which supports the formation of [Fe II (TPP)(NO)] in the reaction medium (Figure 3).…”

“…29 Recently, it was reported that a five-coordinated {MnNO} 6 complex, in the presence of [Fe III (DTC) 3 ], releases NO − . 27 This has been attributed to the fact that [Fe III (DTC) 3 ] dissociates in solution to [Fe III (DTC) 2 ] + and DTC − . This DTC − then acts as the sixth ligand and binds the Mn center of the {MnNO} 6 complex, resulting in the release of NO − .…”

Characterization and Reactivity of an Incredibly Reactive Intermediate in the Protonation Reaction of Dioxo-Manganese(V) Porphyrin with Acid

“…The optimized structures were not largely changed by the functional, except the Mn–OH 2 distance in 3 . The calculated Mn–OH 2 distances (2.50–2.76 Å) in 3 using these three functionals are longer than those (2.1–2.3 Å) reported in X-ray crystal studies of Mn­(III) porphyrins. − The Mn–OH 2 distance using ωB97xD is close to that using the BP86 functional but ∼0.2 Å shorter than that using the B3LYP, probably because of the dispersion effect. The calculated MnO bond length becomes shorter in the order of 1 , 2 , and 3 in the calculations using all of these three functionals because of the trans influence of the axial ligand.…”

Reaction of a nitrosyl complex of Mn(ii)–porphyrinate with superoxide: NOD activity is favoured over SOD activity

“…15 Upon reaction with hydroxylamine, 1a undergoes reductive nitrosylation to yield the complex [Mn(TMPP 2− )(NO)], 1 . 15 Kubiak et al reported a five-coordinated nitrosyl complex of Mn( ii )–porphyrinate with {Mn(NO)} 6 configuration, which then was synthesized by bubbling excess NO gas through a CH 3 OH solution of complex 1a in the presence of NaBH 4 . 16 Complex 1 shows FT-IR stretching frequency at around 1755 cm −1 in KBr, which matches with the reported one.…”