Steroid imines as chiral ligands. Diastereoselective formation of (1-azadiene)Fe(CO)3 complexes by sterically tuning the ligand coordination spheres1Dedicated to Prof. Dirk Walther on the occasion of his 60th birthday.1

The condensation of steroid amines with α,β-unsaturated aldehydes leads to the formation of chiral 1-azadiene ligands with a steroid core attached to nitrogen. If the azadiene chain is situated at the D-ring of the steroid at C16 or C17, respectively, the two diastereotopic faces of the ligand may be discriminated by different neighbouring substituents and their configuration. The reaction of these ligands with Fe2(CO)9 produces mixtures of diastereomeric (1-azadiene)Fe(CO)3 complexes. By increasing the steric demands of the neighbouring groups it is possible to improve the diastereoselectivity of this complexation reaction from 1:1 mixtures using the least sterically hindered ligands to complete diastereoselectivity using the azadiene derived from cinnamaldehyde and 16β-amino-3-methoxy-estra-1,3,5(10)-triene-17β-ol. In addition, the molecular structure of [17β-(3-phenyl-prop-2-enyliden)-amino-3-methoxy-estra-1,3,5(10)-triene]Fe(CO)3 was determined by X-ray structure analysis.