Nitrosyl compounds

Nitrosyl Compounds.—Mn(NO)3PF3 has been prepared by two methods  

Payne and H. Frye, Inorg. Nuclear Chem. Letters, 1973, 9, 505. 

Jacobson, P. Reich-Rohrwig, and A. Wojcicki, Inorg. Chem., 1973,12, 717. 

The loss of an electron by NO should lead to a stable ion [ N=0 ] since this contains a triple bond compared with a 2i-bond (double + 3-electron bonds) in NO. Hantzsch showed that nitrous acid does not exist as HNO2 in acid solution but as NO ions  

Support for this polar structure comes from the dipole moments of pure NOCl and NOBr (2-19 D and 1-90 D respectively) which are much greater than the values (around 0 3 D) estimated for structure (1). 

The structure of [CofCNljNO] has been studied by spectral means. I.r. and electronic spectra indicate it should be reformulated as [(CN)5Co(N202)-CoICNjs] - however, the appearance of v(NO) in range 1770—1860 cm in dilute solution is taken as evidence for a monomer-dimer equilibrium.  

Tamaki, I. Masuda, and K. Shinra, Bull. Chem. Soc. Japan, 1972, 45, 171. 

Jezowska-Trzebiatowska, J. Hanuza, O. Ostern, and J. Ziolkowski, Inorg. Chim. Acta, 1972, 

Cobalt(i).— Anhydrous CoX (X - Cl,Br. or I) can be reduced by BH in the presence of MeC(CH2PPh2)3 to form [CoXL], which are non-electrolytes and isomorphous with the analogous Cu complexes. Pseudo-tetrahedral geometry is proposed.  

---

Several iron sulfide nitrosyl compounds are known. These have stmctures that in some cases are formally related to the FeS clusters by replacement of thiolate by NO. The compounds include the anions [Fe2S2(NO)4] and [Fe4S2(NO)2] (Roussin s red and black salts, respectively) and the neutral compounds [Fe2S2(NO)4] and [Fe4S4(NO)4]. Roussin s black salt has found use as a NO releasing vasodilator. 

Efficient nitrosations of amines with inorganic nitrosyl compounds also have been reported (60). 

These, and related, iron nitrosyl compounds have excited considerable interest because of their biological activity.Nitroprusside induces muscle relaxation and is therefore used to control high blood pressure. Roussin s black salt has antibacterial activity under conditions relevant to... 

Two factors have contributed particularly to the interest in the iridium and rhodium nitrosyl compounds [179] ... 

CEC [Chisso Engineering Company] A process for removing oxides of nitrogen from flue-gases by scrubbing with an aqueous solution containing ferrous ion and ethylenediamine tetra-acetic acid (EDTA). An iron nitrosyl compound is formed. Developed by Chisso Engineering Company, Japan, and piloted in France and Japan. 

Selected Reactions of Metal Nitrosyl Compounds with Nucleophiles... 

The syntheses, structures and properties of wide varieties of metal nitrosyl complexes have been well documented [4, 5, 20-23]. However, the bulk of the complexes reviewed previously are of academic interest and only a few of these metal nitrosyl complexes have been considered as biologically effective NO donors. It was observed that the metal nitrosyls with significant NO+ character are subject to attack from a variety of nucleophiles and have hypertensive properties. This could be due to the strong trans- labilizing effect of NO. In contrast, the metal nitrosyl compounds with the general formula [M(CN)5NO]n, where the NO ligand was either neutral (for M = Co) or anionic (for M = Cr) showed no vasodilatory effect [24]. 

The very close vicinity of the abovementioned 5-values, and the surprising similarity of the optical spectra of Os(OEP)NO(OMe) [31c] and Os(OEP)N(OMe) [25c] are nice examples of the oxidation state ambiguity typical for the nitrosyl compounds the trivial representation of [25c] as a nitridomethoxoosmium(VI) derivative could justify the formulation of [31c] as a derivative of N03e and OsVI instead of NO and Os11. On the other hand, our preference to regard [57c] as a NO derivative (66) could imply the absurd view of [25c] containing a N ion stabilized by coordination. 

Garif yanov, N. S., Luchkina, S. A. EPR study of certain nitrosyl compounds of chromium. Teor. i Eksperim. Khim. Acad. Nauk Ukr. SSR J, 571 (1969). 

Other nitrosyl compounds such as, K[NOBr5lr], K2[NOCLsRu] and [NO(NH3)sRu]Cl3, have also shown vasodilatory activity, presumably by releasing NO, but are too toxic for clinical use. A nitro complex, [Cl(02NXbpy)2Ru], which probably releases NOJ, exhibited higher activity than sodium nitrite [38]. 

Nitric oxide rapidly reacts with transition metals, which have stable oxidation states differing by one electron (see Chapters 2 and 3). Nitric oxide is unusual in that it reacts with both the ferric (Fe " ) and ferrous forms (Fe " ) of iron. TTie unpaired electron of nitric oxide is partially transferred to the metal forming a principally ionic bond. Complexes of ferric iron with nitric oxide are called nitrosyl compounds and will nitrosate (add an NO group) many compounds, while reducing the iron to the ferrous state (Wade and Castro, 1990). 

Payne, M. J., Glidewell, C., and Cammack, R. (1990b). Interactions of iron-thiol-nitrosyl compounds with the phosphoroclastic system of Clostridium sporogenes. J. Gen. MicrO biol. 136, 2077-2087. 

In spite of the above speculation, the actual mechanisms used by NO-pro-ducing nitrite reductases for reduction of nitrite and its activation for nitrosyl transfer are poorly understood. The fact that both the heme and Cu types of enzyme catalyze the reaction is remarkable in view of the fact that nitrosyl compounds of Fe complexes are well known, whereas Cu-nitrosyl compounds are rare [see Garber and Hollocher (1982) and Kim and Hollocher (1984) for further discussion]. On the other hand, both Fe and Cu can coordinate O and this might be more relevant for the activation of an O atom of nitrite for N-O bond breaking. In the case of the Cu-type nitrite reductase of A. cycloclastes, the... 

The nitrosyl compounds can be readily classified on the basis of three modes of reaction of the NO molecule in accordance with the above formulation. 

Nitrosyl compounds of copper, manganese, iron, cobalt, nickel, and palladium... 

The results are consistent with the predictions of the ligand field theory and with the observed photochemical reactions. Bond bending distortions are observed in metal-nitrosyl compounds. The photochemical reactions of CotCCO NO and the photohydrogenation catalyzed by RhCPPhjJ NO provide indirect support for the bending. 

Figure 3.4 Iron-sulfur nitrosyl compounds (a) Roussin s black salt and (b) Roussin s methyl red ester.

---