Cyclopentadienyl-metal-arene complex

Cyclopentadienyl-metal-arene complexes are mostly known with Fe and Ru. The CpM group (M = Fe or Ru) activates many aromatic syntheses (nucleophilic addition and substitution, benzylic deprotonation, etc.). With Fe, they are stable in the 17, 18 and 19e forms with perme-thylated rings, which provides electron-reservoir properties (stoichiometric and catalytic) and proton-reservoir functions (perfunctionalization of polymethylbenzene ligands). 

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