Interactions with arene rings

Yet another variety of self-association via r-interactions was discovered in the solid-state structure of imsolvated 2,4,6-triisopropylphenyllithium. In the crystal this compound forms the tetramer [Li(2,4,6-Pr 3C6H2)]4, 63. This structure has not been observed for other aryllithium species. It consists of an almost planar arrangement of four lithium atoms, each n-bonded to just one phenyl ring (average Li-C distance 2.12 A). In addition, each Li interacts with the 7t-electron system of a 

Ti-lnteractions between phenyl rings and alkali metals can even occur in some more exotic molecular structures as exemplified by the unusual heterobimetallic lutetium butadiene complex [K(THF)2(/r-Ph2C4H4)2Lu(thf) ] , 73 [73]. In 73 the central Lu atom is coordinated by two 4-diphenyl-1,3-butadiene ligands and two THF molecules. Self-assembly with the formation of one-dimensional polymeric chains occurs because potassium forms / -interactions with the -systems of two phenyl substituents from neighboring molecules. 

The structural chemistry of solvated alkali metal derivatives of planar polycyclic hydrocarbon dianions has been well investigated. Monomeric complexes have been isolated with hydrocarbons such as naphthalene, anthracene, perylene, pentalene, 

Most of the remaining examples of supramolecular alkali metal compounds involving r-coordination are alkoxides, siloxides, and thiolates. In polymeric sodium phenolate ( NaOC6H4Me-4 2]n, 79 [78], the / -arene interaction of the phenolate ligands with sodium plays a crucial role, because it restricts the structure of the resulting polymer to a one-dimensional stack of [NaOC6H4Me-4]2 dimers and prevents the formation of a fully extended three-dimensional network. 

The formation of polymeric chains by / -arene coordination to alkali metals has 

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The key initiation step in cationic polymerization of alkenes is the formation of a carbocationic intermediate, which can then interact with excess monomer to start propagation. We studied in some detail the initiation of cationic polymerization under superacidic, stable ion conditions. Carbocations also play a key role, as I found not only in the acid-catalyzed polymerization of alkenes but also in the polycondensation of arenes as well as in the ring opening polymerization of cyclic ethers, sulfides, and nitrogen compounds. Superacidic oxidative condensation of alkanes can even be achieved, including that of methane, as can the co-condensation of alkanes and alkenes. 

The ferrocene moiety is not just an innocent steric element to create a three-dimensional chiral catalyst environment. Instead, the Fe center can influence a catalytic asymmetric process by electronic interaction with the catalytic site, if the latter is directly coimected to the sandwich core. This interaction is often comparable to the stabilization of a-ferrocenylcarbocations 3 (see Sect. 1) making use of the electron-donating character of the Cp2Fe moiety, but can also be reversed by the formation of feirocenium systems thereby increasing the acidity of a directly attached Lewis acid. Alternative applications in asymmetric catalysis, for which the interaction of the Fe center and the catalytic center is less distinct, have recently been summarized in excellent extensive reviews and are outside the scope of this chapter [48, 49], Moreover, related complexes in which one Cp ring has been replaced with an ri -arene ligand, and which have, for example, been utilized as catalysts for nitrate or nitrite reduction in water [50], are not covered in this chapter. 

Longer Hg-7r interactions are observed in the /> ra-/-butylcalix[4]arene mercury complex 162. The mercury atom forms primary bonds with the two sulfur atoms and engages in weaker secondary interactions with two arene rings of the calixarene whose centroids sit at 3.07-3.11 A from the metal center.201... 

Manganese, iron, cobalt, and nickel vapors do not give arene complexes with haloarenes. Interactions with hexafluorobenzene have been reported, but the explosive products are unlikely to be complexes containing planar C8F8 rings. The Ni-C8F8 cocondensate is a source of... 

If one of the cyclopentadienyl rings of ferrocene is replaced with an arene moiety, the Fe(II) complex becomes cationic and hence gains the potential for electrostatic interaction with anions. This concept was first explored by Beer and co-workers using the simple amido[CpFe(arene)]+, 30 [25]. Simi-... 

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