Transition-metal-coordinated arenes

In another interesting series of one-dimensional conductors where the cation is an arene such as perylene, the anion is a transition-metal-coordinated complex [M(mnt)2] which provides an additional degree of freedom, depending on whether the metal atom carries a spin M = Ni, Pd, Pt, etc. or not for M = Au [11]. Superconductivity has also been found in another series of materials based on transition metal complexes M(dmit)2, where M = Ni or Pd with Tc = 1.6 K under 6 kbar [12]. 

By coordinating to arenes, transition metals can facilitate ring lithiation by decreasing the electron density in the ring and acidifying the ring protons. We shall consider briefly the two most important metal-arene complexes in this regard—arenechromium tricarbonyls and ferrocenes. 

This chapter covers reactions in which coordination of a transition metal to the ir-system of an arene ring activates the ring toward addition of nucleophiles, to give V-cyclohexadienyl-metal complexes (1 Scheme 1). If an electronegative atom is present in the ipso position, elimination of that atom (X in 1) leads to nucleophilic aromatic substitution (path a). Reaction of the intermediate with an electrophile (E+) can give disubstituted 1,3-cyclohexadiene derivatives (path b). If a hydrogen occupies the ipso posi-... 

The fact that coordination of the diolefin occurs by displacing the arene also favors the hypothesis that the diolefin coordinates in the cis conformation by the two double bonds. Displacement reactions of this type are well known in organometallic chemistry (See e.g. (2)) and, in the cases already clarified, it has been shown that diolefin coordinates in the cis conformation by the two double bonds. This is not surprising if we consider that the diolefin, coordinated in this way to a transition metal, has a quasi-aromatic character owing to the complete delocalization of the 7r-electrons. 

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