Synthesis of Rh(I) diamine complexes and their exploitation for asymmetric hydrogen transfer processes

In this paper, we report the synthesis and characterisation of two novel chiral diamine ligands and three new Rh( I) complexes. The diamine ligands were prepared by reducing the Schiff base precursors using NaBH4. Unusually, when ligand 2 was recrystallised in a methanol: acetone solution ( 10: 1) a five membered imidazolidine ring was formed, as confirmed by X-ray crystallography, multinuclear NMR spectroscopy and mass spectrometry. The Rh( I) cationic complexes were prepared in high yields and purities and these have been exploited for the asymmetric reduction of acetophenone to 1-phenylethanol. Modest conversions ( up to 88%) and enantioselectivities ( up to 50%) have been achieved. (C) 2008 Elsevier B. V. All rights reserved.