Nitrosyl clusters

The use of NO was successfully applied to Ru3(CO)i2 and Os3(CO)i2 to make the first carbonyl clusters containing nitric oxide as a ligand (12). The nitrosyl ligands bridge the same edge of the triangle in both 

The basic problem of using NO gas with clusters is that this reagent often cleaves the metal-metal bond as well as substituting for a carbonyl ligand. Since NO donates three electrons, displacement of precisely one CO and one M—M bond is feasible. Equations (4) (75), (5) (76), and (6) (77) are excellent examples of this. 

The successful isolation of the intact Ru and Os clusters is due in part to the greater strength of the M—M bonds. 

At this point in time NO has been the most successful reagent for the synthesis of nitrosyl carbonyl clusters. It is usually used as the Bp4 or PFe salt, which should be sublimed prior to use, and in all successful uses 

The difficulty often encountered with NO arises from its high oxidation potential which can easily destroy clusters that are not robust. The reaction of NO with [H30s4(C0)x2] [Eqs. (11) and (12)] exemplifies the different products that can form as well as illustrating the dramatic effect 

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The interactions of NO with the iron-sulfur cluster moieties of several enzymes generate iron-sulfur-nitrosyl cluster compounds [156]. However, synthetic nitrosyl clusters such as Roussins black salt (RBS), Roussins red salt (RRS), Roussins red ester (RRE) and [FeNOS]4 (Fig. 5.3) are well known [129, 157] and can be synthesized easily [158-164]. For example, the RBS can be prepared by mixing FeS04 with NaN03 and (NH4)2S in aqueous solution [158]. RRE salts are generally insoluble in water, but recently the water soluble sulfonated derivative, Na2[Fe2(SCH2CH2S03)2(N0)4], has been prepared [165]. 

There is interest in the possible use of other metal nitrosyl complexes as vasodilators, but from the series KJM(CN)6NO] where M = V, Cr, Mn, and Co (n = 3) or M = Mo (n = 4) neither the Cr nor the Mn complexes exhibit any hypotensive action (504). Iron-sulfur-nitrosyl clusters such as [Fe4S4(NO)4] are active, and their effects can be potentiated by visible light (505). 

Cluster Compounds.—The green nitrosyl cluster Os3(CO)jo(NO)2 has been reported in 13% yield from the reaction of NO with Os3(CO) 2 benzene. Its i.r. spectrum suggests bridging nitrosyl groups, which was confirmed from an X-ray analysis of the Ru analogue. I.r. studies show that the structure (23)... 

Figure 17.3 Thermal and photochemical transformations of iron-sulfur-nitrosyl clusters.

Few successful reactions are known by which an organometallic nitrosyl product has been formed from the condensation of mononuclear metal nitrosyl complexes. The unique cluster (Tj -C5H5)3Mn3(NO)4 (39), which contains the only i3-NO known (7) (40), is prepared using photochemical or thermal (41) decarbonylation of (Tj -C5H5)2Mn2(CO)2(NO)2 [Eq. (25)]. The use of the redox condensation of a nitrosyl carbonylmetallate with a neutral metal carbonyl cluster to produce a nitrosyl cluster has... 

The formation of nitrido clusters from coordinated NO will be discussed first, since it is likely that the other products (NH, etc.) form via coordinated N atoms. In this section we will consider only the reactions of well-characterized nitrosyl clusters. The general condensation of mononuclear nitrosyl complexes to yield nitrido clusters will be discussed in Section III,A,2. 

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