Functionalized Alkali Metal Cyclopentadienides: Structural and Chemical Features

Synthetic routes to alkali metal cyclopentadienides that bear various organic functional groups on their five-membered carbocyclic ring systems are presented and discussed using selected examples. These include carbonyl addition reactions of cyclopentadienides to, for example, alkyl isocyanates to eventually yield carboxamide-substituted cyclopentadienide systems. These and related routes have been used to, for example, prepare peptide-substituted Cp anions. Fulvene routes are very useful for the synthesis of alkenylcyclopentadienides, of imino-Cp compounds, of aminomethyl- or phosphinomethyl-Cp derivatives, and even their respective dianionic analogues. Many of the new functionalized lithium cyclopentadienide examples were structurally characterized. Many of them form well-defined extended oligomeric structures that make specific use of the functional groups in the construction of the supramolecular complex framework. Eventually, first examples of specific carbon−carbon coupling reactions are presented and discussed that take place at the active lithium cyclopentadienide stage, which may lead to the development of a selective functional group chemistry at the alkali metal cyclopentadienides.