Chirality at Metal Half-sandwich Compounds

1 Chiral Three-legged Piano Stool the CpMnL L L Model 

Half-sandwich compounds with three-legged piano stool geometry with different substituents are archetypal examples of optically active chiral-at-metal complexes. In 1969 Brunner et al. prepared and resolved the first chiral organometallic complex with four 

Chirality in Transition Metal Chemistry Molecules, Supramolecular Assemblies and Materials H. Amouri and M. Gruselle 2008 John Wiley Sons,Ltd. ISBN 978-0-470-06053-7 

To complete the resolution, the optically active auxiliary was removed from the separated diastereomers by bubbling HCl through solutions of 3.2a and 3.2b in benzene. During this reaction the C—Omenthyi bond was cleaved. Menthol was formed and the carbonyl group at the metal centre was restored. The counter anion Cl was then replaced by PFg. Thus starting from diastereomer 3.2a ([a]579 = +460 (c = 0.1, benzene)),the PFg salt 3.1a = +375) was formed while the diastereomer 3.2b = —450 

An important issue in these chiral complexes is the configurational stability at the metal centre. A complex may be configurationally stable over weeks while others epimerize or racemize rapidly even at low temperatures. Thus in one case complexes may be 

---

Stability of the metal configuration in chiral-at-metal half-sandwich compounds (with heterocycles as ligands at metal atom) 01EJI905. 

---