Cyclometallation reactions. Part 17. Comparative studies of the manganation and palladation of some substituted azobenzenes

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Abstract
Comparative studies of the manganation {with [MnMe(CO)5]} and palladation (with PdCl2) of several substituted azobenzenes have demonstrated that these complexes behave as nucleophilic and electrophilic reagents, respectively. Assignment of the isomeric structures of the products is facilitated by 19F n.m.r. spectroscopy using fluoroazobenzenes. Metallation of the 2- and 4-substituted azobenzenes XC6H4N:NPh may give products in which the azobenzene has been metallated either in the Ph ring [isomer (a)] or in the substituted ring [isomer (b)]; 3-substituted azobenzenes may give complexes in which the Ph ring has been metallated [isomer (a)], or isomers in which metallation occurs at either of the carbons ortho to the azo-function in the substituted ring [isomers (b) or (c)]. Using XC6H4N:NC6F5 the C6F5 group is not metallated, and the only complexes formed have structures corresponding to isomer (b)(with 2- or 4-substituted compounds), or to isomers (b) and (c)(in the 3-substituted series). Electron-withdrawing substituents activate the aromatic ring to attack by [MnMe(CO)5], while electron-donating substituents activate the ring towards electrophilic attack by PdCl2.

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