Catalytic sugar-assisted transfer hydrogenation with Ru(II), Rh(III) and Ir(III) halfsandwich complexes

• Arene complexes with sugar ligands were applied in asymmetric transfer hydrogenation.
• The complexes under study induce an enantiomeric excess up to 66%.
• The D-gluco- and D-mannopyranoside ligands behave as pseudo-enantiomers.
• The enantiomeric excess is supported by the substitution pattern of the arene ligands.
• With DFT calculations the favored transition states could be identified.

The application of halfsandwich ruthenium(II), rhodium(III) and iridium(III) complexes of four different methyl 2,3-diamino-4,6-O-benzylidene-2,3-dideoxy-α-D-hexopyranosides and a methyl 2-amino-3-tosylamido-α-D-glucopyranoside as catalyst precursors in asymmetric transfer hydrogenation of acetophenone is reported. The configuration of the hexopyranosides and the type of arene ligands determine the formation of R- or S-1-phenylethanol up to 66% ee. A large influence of the substitution pattern of the arene ligands on the extent of the enantiomeric excess is demonstrated. The results are interpreted by means of DFT calculations.

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