European researchers have developed a choice of routes to [3]ferrocenophanones, important building blocks for ligands used in asymmetric catalysis.

Gerhard Erker at Universität Münster, Germany, and colleagues prepared a methyl-substituted [3]ferrocenophanone in several ways from a simple starting material. 

Erker used a Mannich-type reaction (carbon-carbon coupling) to close the carbon bridge between the two aromatic rings of a ferrocene-based molecule. The result is an amine that can be converted to the desired ketone in a number of ways. Erker's group separated the enantiomers of the amine intermediate, allowing the researchers to prepare final product in enantiomerically pure form.

Ferrocenophanones are important starting materials for a series of ligands used in asymmetric catalysis, the ferrocenophanes. Both are derivatives of ferrocene, a molecule in which an iron atom is sandwiched between two aromatic rings. In ferrocenophanes these two rings are connected by a carbon-atom bridge, forming a third ring.  Ferrocenophanones are similar structures in which one, or more, of the bridging atoms is part of a carbonyl group.

 

    

 

Conventional methods of making the carbonyl derivatives, though excellent for some systems, are not always reliable and can fail in sterically hindered cases, according to Erker. 

He said that the special characteristics of the carbonyl group and the unique features of the ferrocene core are likely to allow selective attachment of various functional groups to the derivatives and hence lead to the 'development of novel ligand systems and improved catalytic processes'.

Celia A. Clarke