Synthesis, structure, and catalytic activity of some new chiral 2-menthylindenyl and 2-menthyl-4,7-dimethylindenyl rhodium complexes

Optically active rhodium complexes containing the chiral, menthyl-substituted indenyl ligands (-)-2-menthyl-4,7-dimethylindene and (-)-2-menthylindene are described. Metathesis reactions of the chiral lithium salts of these indenyl systems with the appropriate starting materials yielded the complexes (-)-(2-menthyl-4,7-dimethylindenyl)Rh(CO)₂ (2), (-)-(2-menthyl-4,7-dimethylindenyl)Rh(dppe) (3), (+)-(2-menthylindenyl)Rh(dppe) (5), (-)-(2-menthylindenyl)Rh(PMe₃)₂ (6), and (-)-(2-menthylindenyl)Rh(nbd) (8). All compounds obtained were diastereomerically pure. The structures of 2, 3, and 6 were determined by single crystal X-ray diffractometry. Complexes 3 as well as (-)-bis(η²-ethylene)(η⁵-2-menthyl-4, 7-dimethylindenyl)rhodium(I) (9), (-)-(cycloocta-1,5- diene)(η⁵-1-menthyl-4,7-dimethylindenyl)rhodium(I) (10), (-)-(cycloocta-1,5-diene)(η⁵- 2-menthyl-4,7-dimethylindenyl)rhodium(I) (11), and (-)-(cycloocta-1,5-diene)(η⁵-2- menthylindenyl)rhodium(I) (12) were found to be active as double bond hydrogenation catalysts. Two of them proved to induce asymmetry up to 18% ee. These complexes also promote the hydroformylation of olefins yielding both linear and branched aldehydes in varying ratios but hardly transfer chirality.