The Electrophilic Reactions of Pentacyanonitrosylferrate(II) with Hydrazine and Substituted Derivatives. Catalytic Reduction of Nitrite and Theoretical Prediction of η¹-, η²-N₂O Bound Intermediates

Abstract

The electrophilic reactivity of the pentacyanonitrosylferrate(II) ion, [Fe(CN)(5)NO](2)(-), toward hydrazine (Hz) and substituted hydrazines (MeHz, 1,1-Me(2)Hz, and 1,2-Me(2)Hz) has been studied by means of stoichiometric and kinetic experiments (pH 6-10). The reaction of Hz led to N(2)O and NH(3), with similar paths for MeHz and 1,1-Me(2)Hz, which form the corresponding amines. A parallel path has been found for MeHz, leading to N(2)O, N(2), and MeOH. The reaction of 1,2-Me(2)Hz follows a different route, characterized by azomethane formation (MeNNMe), full reduction of nitrosyl to NH(3), and intermediate detection of [Fe(CN)(5)NO](3)(-). In the above reactions, [Fe(CN)(5)H(2)O](3)(-) was always a product, allowing the system to proceed catalytically for nitrite reduction, an issue relevant in relation to the behavior of the nitrite and nitric oxide reductase enzymes. The mechanism comprises initial reversible adduct formation through the binding of the nucleophile to the N-atom of nitrosyl. The adducts decompose through OH(-) attack giving the final products, without intermediate detection. Rate constants for the adduct-formation steps (k = 0.43 M(-)(1) s(-)(1), 25 degrees C for Hz) decrease with methylation by about an order of magnitude. Among the different systems studied, one-, two-, and multielectron reductions of bound NO(+) are analyzed comparatively, with consideration of the role of NO, HNO (nitroxyl), and hydroxylamine as bound intermediates. A DFT study (B3LYP) of the reaction profile allows one to characterize intermediates in the potential hypersurface. These are the initial adducts, as well as their decomposition products, the eta(1)- and eta(2)-linkage isomers of N(2)O.

Nucleophilic Addition Reactions of the Nitroprusside Ion – The Case of O‐Methylhydroxylamine

“…The results in Table 3 suggest a similar interpretation for primary amines and for hydrazine. In fact, the side‐on η 2 ‐N 2 O intermediate has already been proposed, resulting from the N–N cleavage ensuing from the binding of hydrazine to [Fe(CN) 5 NO] 2– , with concomitant formation of NH 3 7. Moreover, the previous calculations also suggest that the side‐on intermediate evolves to the end‐on isomer before N 2 O release 16…”

“…An example of this chemistry is represented by the nitrosyl group,2 which includes a role for stabilized metal–NO moieties that behave as crucial intermediates in the reactivity of NO 2 – . The nitroprusside ion, [Fe(CN) 5 NO] 2– , is an electrophile toward a variety of substrates,3 reacting with N‐binding nucleophiles such as NH 3 4 and NH 2 R,5 NH 2 OH,6 N 2 H 4 ,7 as well as with others like OH – ,8 HS – ,9 and thiolates 10. In this way, different reduction products of NO + can be obtained.…”

Electronic structure of metastable isomers of Ru nitroso complexes

“…Metastable isomers MS1 were experimentally detected for the above compounds, while the MS2 isomers were only found in [ Ru ( NO )(ë N ) 5 ] 2- [14] and [ Ru ( NO )(ë l ) 5 ] 2- [15]. Intermediates with a side η 2 -coordination of N 2 O, which were obtained theoretically when modeling the coordinate of reaction between [ Fe ( CN ) 5 NO ] 2-and hydrazines [12] are also considered in the context of the studies of the linkage isomers for the coordinated small molecules.The structural characteristics of the nitroso complexes [ Ru ( NO )( X ) 5 ] q (X = NH 3 , Cl -, CN -) and trans -[ Ru ( NO )( NH 3 ) 4 ( L )] 3+ (L is imidazole (Im), pyridine (Py), pyrazine (Pyz), Nc) were calculated by the DFT method in [16]. In addition to a stable structure with the η 1 -coordination of the nitroso group through the N atom (GS), each of the above complexes exhibited two metastable isomers MS1 and MS2.…”

“…Metastable isomers MS1 were experimentally detected for the above compounds, while the MS2 isomers were only found in [ Ru ( NO )(ë N ) 5 ] 2- [14] and [ Ru ( NO )(ë l ) 5 ] 2- [15]. Intermediates with a side η 2 -coordination of N 2 O, which were obtained theoretically when modeling the coordinate of reaction between [ Fe ( CN ) 5 NO ] 2-and hydrazines [12] are also considered in the context of the studies of the linkage isomers for the coordinated small molecules.…”

“…Much attention is given to the quantum chemistry of nitroso complexes. The quantum-chemical calculations of Ru complexes were performed aimed at the search of metastable isomers [2][3][4][5][6][7]; their UV and visible spectra were assigned in [8][9][10]; the mutual effect of their ligands was studied and the proposed intermediates in the reactions with participation of the coordinated NO were modeled [11][12][13]. 1 The structural and energy characteristics of isomers with the linear η 1 -coordination of NO through the oxygen atom (MS1) and with the side η 2 -coordination of NO (MS2) were obtained for the [ Ru ( NO )( NH 3 ) 5 ] 3+ and [ Ru ( NO )( CN ) 5 ] 2-complexes [4].…”