Nitrosyl clusters reduction

In recent years, several model complexes have been synthesized and studied to understand the properties of these complexes, for example, the influence of S- or N-ligands or NO-releasing abilities [119]. It is not always easy to determine the electronic character of the NO-ligands in nitrosyliron complexes thus, forms of NO [120], neutral NO, or NO [121] have been postulated depending on each complex. Similarly, it is difficult to determine the oxidation state of Fe therefore, these complexes are categorized in the Enemark-Feltham notation [122], where the number of rf-electrons of Fe is indicated. In studies on the nitrosylation pathway of thiolate complexes, Liaw et al. could show that the nitrosylation of complexes [Fe(SR)4] (R = Ph, Et) led to the formation of air- and light-sensitive mono-nitrosyl complexes [Fe(NO)(SR)3] in which tetrathiolate iron(+3) complexes were reduced to Fe(+2) under formation of (SR)2. Further nitrosylation by NO yields the dinitrosyl complexes [(SR)2Fe(NO)2], while nitrosylation by NO forms the neutral complex [Fe(NO)2(SR)2] and subsequently Roussin s red ester [Fe2(p-SR)2(NO)4] under reductive elimination forming (SR)2. Thus, nitrosylation of biomimetic oxidized- and reduced-form rubredoxin was mimicked [121]. Lip-pard et al. showed that dinuclear Fe-clusters are susceptible to disassembly in the presence of NO [123]. 

Reductive nitrosylation, transition metal nitrosyl complexes, 34 296-297 ReFejSj cluster, 38 41-43 self-assembly system, 38 41-42 Refining, of actinide metals, see Actinide, metals, purification Refractory compounds heat treatment of solids, 17 105-110 crystal growth, 17 105, 106 decomposition, 17 107,-110 spheroidization, 17 106, 107 preparation of, using radio-frequency plasma, 17 99-102... 

Reduction of the nitrosyl group occurs in certain cases, providing an effective method for the synthesis of nitrido clusters. For example (19) ... 

In the managanese system [Mn3(i7-C5Me5)3(/i,-NO)3(/i,3-NO)] (279), very similar chemistry is observed but in addition, reduction of the nitrosyl group occurs, yielding the imido cluster [Mn3(i7-C5Me5)3(/u,3-NH)(/i2-NO)3] in low yield. Such a reaction undoubtedly proceeds by a nitrido intermediate, though the exact mechanism is, at present, unknown. 

The two isostructural clusters [Co6N(CO)i5] and [Rh6N(CO)i5] were synthesized by reaction of the octahedral clusters [M6(CO)i5] (M = Co, Rh) with nitrosonium tetrafluoborate. Better yields of the rhodium species were obtained by treatment, in a strongly reducing medium, of [RhyjCOjie] " with NO (diluted 1 1 with CO). The reactions are complex and no intermediate step could be identified. However, a nitrosyl derivative is very likely to be involved, and subsequent reduction, by the reaction medium or the starting reduced carbonyl itself, would yield the nitrido cluster. 

Compared to the more extensively studied metal clusters of NO, there are only a handful of examples of monomeric or dimeric nitrosyl complexes undergoing N-O bond dissociation. Cummins and coworkers [117] reported novel in-termolecular NO reductive cleavage reactions of chromium nitrosyl complexes utilizing a highly reactive low-coordinate V htriaryl complex (THF)V(Mes)3 (Mes = 2,4,6-C6H2Me3) as the 0-atom acceptor (Scheme 2.4). 

---