Multiple-decker sandwich

The most unusual geometries among these types of clusters are clearly the multiple-decker sandwich structures observed for vanadium ion-benzene clusters Vn(C6H6)+ [142, 151-157]. One interesting finding is that early transition metals all appear to form sandwich compounds with benzene but for the late metals the benzene adducts coat a central metal cluster [158]. 

Several examples illustrate how organometallic molecules are strikingly different from those encountered in classical inorganic and organic chemistry. Ligands1 of cyclic delocalized n systems (e.g., benzene or cyclopentadienyl) can team up with metal atoms to form sandwich compounds with a metal sandwiched between them. Sometimes atoms of other elements, such as phosphorus or sulfur, can be included as well. Examples of these double- and multiple-decker sandwich... 

Nagao S, Kato A, Nakajima A, Kaya K (2000) Multiple-decker sandwich poly-ferrocene clusters. J Am Chem Soc 122 4221-4222... 

Observed magic-number behavior and ionization energies are consistently explained by assuming the structure of the clusters to be multiple-decker sandwiches forn — m (m = n +, 1-3) and... 

Gas Phase Experiments. - In gas phase laser ablation experiments with organic ligands, novel organometallic network structures were obtained. With 3d transition metals and benzene, two kinds of structures, multiple sandwich and rice-bair, were formed, depending on the nature of the metal. The multiple-decker sandwich structures were also formed with lanthanide atoms and COT. Not surprisingly, such clusters consist of positively charged Ln ions and COT dianions. Their electronic structure is fairly ionic and is localized around each metal atom. ... 

There has been considerable interest in the synthesis of polymers such as structure (6) in which aromatic rings and metal atoms alternate, due to the possibility of building extended electron-delocalized organometallic polymer chains. However, such a multiple decker polymer has not yet been synthesized, and only a few triple decker-sandwich compounds such as tris( 5-cyclopentadienyl)dinickel cation and tris-(cyclooctatetraene)dititanium dianion have been reported10. ... 

Siebert and Herberich have systematically synthesized boron-containing electron-deficient rings, especially because they found that these rings were excellent stabilizers of the triple-and multiple-decker structures. For instance, borole C4H4BH (4e) and 2,3-dihydro-1,3-diborole (3e) are bonded to the metal in a pentahapto fashion as Cp, yet they have and bring a reduced number of k electrons. The tripledecker sandwich complexes formed herewith can have different oxidation states as known in transition-metal sandwich chemistry. - ... 

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