Nucleophilic addition arene-metal complexes

M. F. Semmelhack, Nucleophilic Addition to Arene-Metal Complexes, in Comprehensive Organic Synthesis (Ed. B. Trost, Pergamon, Oxford, U.K., 1991, Vol. 4, pp. 517-549). 

Addition of Oxygen Nucleophiles to Transition Metal 7r-Arene Complexes 685... 

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 first arene-transition metal complexes were prepared in the 1950s1314 and it was immediately recognized that the added polarizibility or electron deficiency would promote addition of nucleophiles to the arene ligand. A number of cyclohexadienyl complexes were characterized following nucleophilic addition, but the question of inducing the ipso hydrogen to depart was not answered (equation 1). 

Numerous synthetically useful carbon-carbon bond-forming reactions are based on the fact that unsaturated hydrocarbon ligands bound to electrophilic transition metal moieties are activated toward addition of nucleophiles. Normally the metal moiety in such complexes is a neutral or cationic metal carbonyl group. Prominent and well-studied examples include [Cr(arene)(CO)3] complexes (covered in Chapter 2.4, this volume),1 [Fe(dienyl)(CO)3]+ complexes (covered in Chapter 3.4, this volume),2 [FeCp(CO)2(alkene)]+ complexes3 and [M(CO) (diene)] complexes.4... 

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