Electrophilic substitution, aromatic complexing with substituent

Electrophilic substitution, aromatic, 31, 130-167, 381 1,2-ti. 1,4-addition, 195 as addition/elimination, 133 complexing with substituent, 160 deuterium exchange, 131,158 electronic effects in, 148, 158, 159 energetics of, 132, 136 field effect in, 152 hyperconjugation in, 153 inductive effect in, 22,152,153,156, 160... 

Ferrocene, Fe(Ti5-C5H5)2, and related cyclopentadienyl complexes of transition metals in fact are far more thermally stable, less reactive substances than ionic cyclopentadienides, and have an extensive derivative chemistry that is typically aromatic in that their C-H bonds can undergo such electrophilic substitution reactions as Friedel-Crafts alkylation or acylation, nitration, and so on. Moreover, as a substituent, the ferrocenyl group (ri -f sl l5)Fc(ri -( 5l I4) (=R) is even more effective than a phenyl substituent in stabilizing carbenium ions [RCH2]+. The redox and photochemical properties of many metaUocenyl residues make them versatile substituents with many chemical and materials applications. ... 

Aromatic compounds react with palladium(II) salts such as PdCOAc) and Na2PdCl4 via an electrophilic aromatic substitution process to give arylpalladium complexes. This type of reaction is most commonly observed with aromatic rings bearing a substituent that makes a fi e- or six-membered chelate ring with palladium in the metallation products (eq (87)) [118]. In this case, the electrophilic substitution occurs only at the ortho position to the chelating substituent. 

The previous sections leave no doubts that aromatic compounds, react with positively charged electrophiles to form a-complexes-arenium ions. But are they the primary intermediates It is not by accident that the problem of preliminary formation of radical cations has arisen. Its statement is an attempts to explain the orientational peculiarities of electrophilic aromatic substitution of hydrogen. The widespread view that the orientation in the reactions of aromatic compounds with electrophiles is dictated by the relative stabilities of the cr-complexes explains but a part of the accumulated material. In the first place this refers to the meta- and para-orienting effects of electron-releasing substituents in benzene in terms of the QCT -approach and to that of the relative reactivity of various aromatic substrates... 

Aromatic compounds react with mercuric salts to give arylmercury compounds. The reaction shows substituent effects characteristic of electrophilic substitution, and is accelerated by electron-releasing substituents. Mercuration is one of the few electrophilic aromatic substitutions in which proton loss from the cr-complex is rate-determining. The reaction exhibits an isotope effect of about... 

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