Clusters cubane types

Among the clusters derivatized by these methods, [ Mo(tacn) 3(PdCl)(n3-S)4]3+ (tacn = 1,4,7-triazacyclononane) is noteworthy, since this cluster can bind the substrate molecules such as alkene and CO at its tetrahedral Pd site generated by dissociation of the Cl anion. More interestingly, it has turned out that addition of ROH and RCOOH to various alkynes proceeds at this Pd site to give vinyl ethers and vinyl carboxylates catalytically.53 These reactions represent one of the yet rare examples that are catalyzed by well-defined cubane-type clusters with retention of their core structures. 

Figure 13 Syntheses of cubane-type clusters starting from incomplete cubane-type Mo3S4 aqua cluster...

Figure 16 Single cubane-type and corner-shared double cubane-type clusters derivedfrom the incomplete cubane-type sulfido-hydrosulfido cluster [(Cp Ir)3(p3-S)(p2-...

Bonding concepts for cubanes, as discussed in Chapter 2.3., predict that the metal polyhedra in the cubanes will contract upon oxidation because of increased metal-metal interaction and vice versa. This has been verified for [CpFeS] 381), [CpFe(CO)]4 167, 177), and [CpCoS]4 361). Furthermore, the ease of oxidation and reduction of several cubane-type clusters 166,167, 361, 381), and the delocalization of electrons in the charged species 48, 176,177, 401) is noticeable. This, together with the prefered formation of iron-sulfur clusters, 381), is borne out by the fact that Nature uses iron-sulfur proteins for redox reactions 207). 

II. Incomplete Cubane-Type Clusters with Mo304. S Cores... 

In contrast to the situation a decade ago, many incomplete cubane-type clusters with Mo304 S cores have been prepared and the structures have been determined by X-ray structure analyses. The results obtained are summarized in Tables I—III. The formal oxidation state of molybdenum in the compounds cited here is in all cases IV. Unlike Mo(VI) and Mo(V) compounds, mononuclear oxo or dioxo compounds of the Mo(IV) state are relatively rare and all the incomplete cubane-type compounds cited here have no terminal oxo ligand. Three Mo atoms form an equilateral triangle, and three single bonds exist between each Mo. Except for the compounds 1, 8, and 31 (Table III), and excluding Mo—Mo bonds, each molybdenum is octahedrally coordinated. 

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