Clusters chalcogen bridged

Scheme 3.2 General synthesis route for the formation of phosphine-ligated, chalcogen-bridged copper clusters.

The use of silylated chalcogen reagents in the synthesis of chalcogen-bridged metal clusters has produced a remarkable number of complexes with a variety of structural types. The nuclearities and structures of these complexes can be highly dependent on the reaction conditions, the steric demands of the ancillary and/or chalcogenolate ligands, as well as the ratio M E. Complexes... 

Several chalcogen-bridged clusters of the group 12 metals (Zn, Cd, Hg) have been synthesized utilizing silylated reagents. Mostly, the structures of these complexes are based on adamantane-like cages, and are similar to II-VI clusters synthesized by other approaches, as described in... 

Table 18 Chalcogen-bridged clusters of the /-block elements.

Chalcogen Bridged D ansition Metal Clusters with i/ -Cydopentadienyl, /13-Allyl, and CO Ligands... 

Finally, the stereodynamics of two mercury-containing metal clusters have been reported. The mercury-bridged osmium cluster [ (ju-H)(/i3-S) (C0)90s3 2(/i4-Hg)] exhibits variable-temperature NMR spectra which are attributed to movements of both fi-Hg and /i-H moieties at comparable rates. Mercury halides form adamantane-like anions with chalcogen bridges. The resulting structures [( i-ER)6(HgX)4] (E = S, Se, Te X = C1, Br, I) have been examined in solution by Se, Te, and Hg NMR spectroscopy. The species tend to dissociate in solution. Pyramidal inversions at Se and Te atoms are slow on the NMR time scale at reduced temperatures, but tend to become rapid at ambient temperatures. ... 

It should be kept in mind that it is often difficult to ascertain what the active catalyst is. There are, in fact, very few proven catalytic mechanisms where the structure of the actual catalyst is known with certainty. There are, to the author s knowledge, few, and possibly no, proven useful homogeneous catalytic processes that involve metal dimers in the catalytic cycle. In an excellent review on cluster catalysis, Muetterties lists the following processes as metal-cluster-catalyzed reactions (see Table 2). This review also lists the important classes of metalloenzyme clusters however, these compounds do not normally involve metal-metal bonds per se but are usually bridged by chalcogens, such as sulfur or oxygen donors. 

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