CHIRAL CO-EMULATING LIGANDS - FROM ARENE CHROMIUM CHEMISTRY TO ENANTIOSELECTIVE CATALYSIS

A one pot nucleophile/electrophile addition/hydrogenation sequence was applied to [(benzene)Cr(CO)(3)] to give predominantly the 4,5-trans-d isubstituted cyclohexene. Several asymmetric modifications of the sequ ential addition of C-nucleophiles and C-electrophiles to (arene)Cr(CO) (3) complexes are discussed. A mechanistically intriguing route involv es the use of chiral phosphorous ligands to control the diastereoselec tivity in the migratory CO insertion step and/or the reductive elimina tion step in the sequence. Ephedrine and norephedrine derived ligands gave product ee of up to 69 %. New C-2-chiral bidentate ligands (L()) which emulate some of the bonding characteristics of CO were synthesi zed and briefly considered for this application. The main interest in these ligands concerns their potential in catalytic C-C bond forming r eactions; a first application to the Lewis acid [CpFeL()](+) catalyze d Diels-Alder reaction between enals and dienes was successfully reali zed.