Nitrosyl clusters synthesis

N NMR spectroscopy, 32 364-365 heterometallic cluster synthesis by nitrosylation of performed heterometallic aggregates, 32 350-351 from sulfur-rich metal complexes, 32 352-353... 

These methods have also been applied to the synthesis of nitrosyl cluster compounds (24, 25) ... 

An important recent development in this class of reaction has been the use of bis-(triphenylphosphine)iminium (PPN) nitrite. This reagent has proved to be particularly useful, especially in the synthesis of nitrosyl cluster compounds from the more readily available carbonyl clusters under mild conditions 43, 44) ... 

The preparation and X-ray crystal structure of [Ru5C(CO)i3(Ti -C4Ph4)], the first cluster to carry a cyclobutadiene ring, has been reported . The synthesis and X-ray crystal structure of the nitrosyl cluster [Ru6C(CO)i4(NO)( j,-ti3-C3H5)], which contains a fluxional allyl moiety has been reported i . 

It is instructive, in this context, to compare the case of assembly of both nitrosylated iron sulfur tetranuclear clusters and the related clusters with pendant thiolate groups (13), with the laborious and stepwise initial synthesis (38) of cubane C8H8 this comparison is, of course, simply one between thermodynamically controlled processes, in the case of the iron sulfur systems, and kinetically controlled reactions for C8H8 synthesis. 

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... 

Although it is not strictly an organometallic cluster, Roussin s Black salt, [Fe4(S)3(NO)7] , represents the first nitrosyl compound prepared via nitrite. The reaction of FeS04, NaN02, and (NH4)2S is perhaps the most convenient method of synthesis of this cluster (29). A better defined approach to the use of N02 was first introduced by Hieber with Fe(CO)s [Eq. (15)] (30). The direct extension of this reaction to Mo(CO)6... 

By far the most pervasive use of the condensation of mononuclear fragments to form nitrosyl-containing cluster has been in the synthesis of cubane-type clusters (48-51). Although most of these are not formally organometallic clusters, the reagents used as starting materials are. Equations (27)-(29) are typical of these condensations. 

The use of nitrite (NO ) as a source of metal nitrosyls is now well established as discussed in Section II,A3. One study of the reaction of PPN(N02) with carbonyl clusters of the Co triad revealed an alternative synthesis of [Co6N(CO)i5] and [Rh6N(CO)i5] "(i5). As shown in Eqs. (48) and (49), both the tetranuclear and hexanuclear starting materials for Rh lead to the same nitrido cluster. The reasonable yields for Rh by either route suggest that the product is somewhat of a thermodynamic sink. Consistent with this idea, Eq. (50) shows the use of gaseous nitric oxide itself to form the Rh nitrido cluster directly (J). 

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

No detailed mechanistic study of these reactions has been made, and there is little evidence to support the intermediacy of nitrosyl or dinitrogen oxide complexes. Since this report, much interest has been shown in the efficient synthesis of oxide-bridged clusters and dimers of IIIA-VIA metals using nitrogen oxides as the oxidizing agents. The following reactions provide t5q)ical examples (205 207) ... 

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