Abstract
Amidation reactions of ferrocene phosphinocarboxylic acids and various simple or functional amines provide access to a range of specific metalloligands combining the soft phosphine moiety with easily changeable, hard-donor amide substituents. Compounds of this type are also accessible in a complementary manner, as demonstrated by the reactions of [1'-(diphenylphosphino)ferrocenyl]methylamine with carboxylic acids (or their derivatives) and isocyanates.
Owing to their hybrid nature, phosphinoferrocene carboxamides are versatile ligands for coordination chemistry and catalysis. Applications in such areas particularly benefit from the modular structures of these compounds, which allow the design and synthesis of extensive ligand libraries and, hence, the fine tuning of their properties for a particular use.
Moreover, phosphinoferrocene amides can easily be made chiral using either a chiral ferrocene precursor or an attached chiral pendant. The amide linking group stabilizes the phosphinoferrocene moiety towards oxidation and endows phosphinoferrocene amides with the ability to participate in hydrogen bonding interactions and, consequently, form well-defined supramolecular assemblies in the solid state.
As a defined linker, the amide moiety can be used to attach phosphinoferrocene moieties onto a larger scaffold (e.g., dendrimers) and thus create multidonor arrays. Furthermore, the presence of the amide moiety renders the phosphinoferrocene carboxamides useful synthetic building blocks.