Sandwich compounds multidecker

The borole ring and various 1,3-diborolyl anions have been extensively employed as ligands to prepare a huge array of transition metal complexes and multidecker sandwich compounds.96 97 Inevitably, the electronic character of the borole is profoundly changed upon complexation, so a study of such complexes can reveal nothing certain about B—C multiple bonding in the isolated ligand. 

Figure 3.24. Routes to multidecker sandwich compounds incorporating C2B3 rings.

Both CgB2 and CgB -based systems have been used to construct multidecKer sandwich compounds.Reaction of bls(allyl) nickel and... 

Multidecker sandwiches and coordination compounds, formed by unstable organic particles such as radicals, biradicals, carbenes, and carbynes [7,112,113] (see Sec. 2.2.4.1), also belong to MCCC. 

These systems exhibit considerable affinity for halide anions. X-ray analysis ascertained the formation of an anionic 2 1 chloride adduct of (1) where the chloride is simultaneously bound by four mercury atoms. In the crystal structures of (2) Cl and (2) l2, the anions are located within the macrocycle and complexed cooperatively by the four mercury(II) centers. Several anionic complexes of (3), including bromide, iodide, and thiocyanide salts, have been isolated. The compounds adopt multidecker stmctures with the hexacoordinated anions effectively sandwiched between two successive molecules of (3). The Lewis acidity of perfluoro-ortAo-phenylenemercury (3) has also been substantiated by its ability to form stable adducts with neutral substrates (HMPA, DMSO, ethyl acetate, and acetonitrile) and arenes. The (3) -CeHe adduct exists as extended stacks of nearly parallel, staggered molecules of (3), which sandwich benzene molecules. Similar structures have been reported for the corresponding adducts with biphenyl, naphthalene, pyrene, and triphenylene. 

In addition to biscyclopentadienyl sandwich-type complexes, triple-decker and multidecker compounds are known.[structures (9.10)]. 

In a kind of inversion of this concept, hydrocarbons can also serve as platforms for polycluster systems the tri- and tetrametallic complexes shown in Chart 8 (A and B) were recently prepared in our laboratory and characterized via X-ray crystallography at the University of Heidelberg (59). Compounds of this type are prototypes for extended oligomeric and polymeric networks such as that proposed in Chart 8(C), that are expected to exhibit extensive electron-delocalization between the metal centers (60). Systems of this kind, together with alkynyl-and phenyl-linked polyhedra, and multidecker sandwich-based arrays, are current targets of our research (61). 

---