Arene substituted clusters

This compound was shown not to be a complete novelty by the preparation of Ru6(CO)i7C (94, 211, 324) and the arene-substituted derivatives Rue(CO)i4(arene)C (211). The latter were obtained by refluxing Rug(CO)i2 in the appropriate arene (mesitylene, m-xylene, or toluene) or by reaction of the arene with the hexanuclear cluster. Ru6(CO)i7C was obtained by refluxing Ru3(CO)i2 in a variety of high-boiling inert solvents such as octane and nonane. Structural studies revealed the position of the carbon atom, in this case at the center of the regular octahedron or ruthenium atoms and equidistant from all six of them (296, 349) (Fig. 3). 

Acetylenes are not the only compounds with organic tt systems which can substitute in metal carbonyls, and the same general synthetic methods can be used for other ligands. Reaction of carbonyl clusters with polyolefin systems, such as 1,5-cycloocatadiene and 1,3,5,7-cyclo-octatetraene, have produced substituted carbonyl systems, but only with Ru3(CO)i2 have clusters been isolated. Arene-substituted carbonyl clusters have also been obtained, as has been described in Section II.D.l. 

As mentioned above, polymorphism may also arise for compounds formed by isomers whose structures are related by low-energy interconversion pathways, e.g. cluster carbonyls with different distributions of bridging and terminal ligands, or substituted metallo-arenes and metallo-cyclopentadienyl complexes [60]. In such cases, the structural isomers correspond to different energetic minima along the interconversion pathway and the cohesion of the respective crystals may stabilize the less thermodynamically stable isomers. Crystals of structural isomers may (or may not) interconvert via a phase transition. 

The chemistry of Ru and Os compounds with metal-carbon bonds is extremely extensive and complicated. Much of this chemistry involves organic groups such as C5H5 and its substituted derivatives and arenes, effectively as spectator ligands, other groups being present as ligands. There is also an extensive chemistry of carbonyls like Ru3(CO)12 and other Ru and Os clusters. We can deal here only with some of the simpler compounds, especially those with M—C, M=C, MCp, and M(arene) bonds. 

The family of 19-electron complexes [Fe Cp(/7 -arene)] has also been investigated as catalysts for the substitution of one, two and three carbonyls in metal-carbonyl clusters as shown below. 

The carbonyl clusters substituted by acetylenes, olefins, and arenes are listed in Table VII, together with their methods of preparation and references to structural studies. 

Substituted styrenes cluster complexes with face-capping arene ligands... 

Entirely different products are formed from la and methyl substituted styrenes. With a- or jff-methylstyrene the trinuclear cluster complexes 13 with face-capping arene ligands were isolated in high yields. A large number of similar complexes has subsequently been prepared from either of la, lb or 2 and substituted styrenes, allylbenzenes and related phenyl-containing olefins (Table 1). 

There is ample chemical evidence that the 1-alkenyl substituent on the arene plays a crucial role during the assembly of the metal cluster. For example, no arene cluster complexes are formed with alkyl substituted benzene derivatives. Such complexes, 14, are perfectly stable and could be obtained indirectly through hydrogenation of the corresponding /rs-alkenylbenzene precursors (Table... 

Braga and Grepioni have undertaken a series of analyses of the crystal structures of metal carbonyl clusters, 7t-arene complexes, mixed carbonyl n-arene complexes and some substituted derivatives [170]. Their analyses are based on examination of the packing details and motifs in the crystal structures, recognition of specific interactions, calculation of the packing potential energy for the crystal and consideration of contributions to the lattice volume. Their objective, to investigate the interplay between molecular structure and crystal structure, is very similar to the perspective in this article. 

Generalized ligand substitution reaction (24) proceeds with a variety of anionic ligands such as halides, thiolates, and arene oxides. Certain neutral ligands also substitute on the 6484] core, notably isonitriles and tertiary phosphines. Although nitrosyl clusters are not within the purview of this section, we note the existence of cubane-type [Fe4S4(NO)4] . Iron-sulfur-nitrosyl... 

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