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.

Graphical abstractThe synthesis, characterisation and catalytic activity of three new Rh(I) complexes are reported, together with the unusual product obtained from the recrystallisation of one of the diamine ligands in acetone.Figure optionsDownload full-size imageDownload as PowerPoint slide