The synthesis and X-ray structure of a chiral rhodium–NHC complex: Implications for the use of NHCs in asymmetric hydroformylation catalysis

An optically active N-heterocyclic carbene (NHC) has been metallated with [RhCl(COD)]2 to give a rhodium(I) monocarbene substituted complex. This complex has been fully characterized by 1H and 13C NMR spectroscopy and by single-crystal X-ray analysis. Preliminary tests of hydroformylation of styrene catalyzed with this compound have shown that branched to linear aldehyde ratio was rather low 0.67 (40%) and that the enantiomeric excess measured on the corresponding alcohols was only 10%. In the presence of an excess of triphenylphosphine, the ratio of branched to linear aldehyde increased markedly (91%) whereas the enantioselectivity of the reaction remained almost unchanged (12.5%).

The synthesis of a new optically active rhodium(I) NHC complex is described and its structure determined by single-crystal X-ray diffraction. Preliminary tests of asymmetric hydroformylation of styrene with this compound are reported.Figure optionsDownload as PowerPoint slide