Optically active transition-metal complexes. 104. Asymmetric Michael reactions of iron complexes (RFe)- and (SFe)-[(.eta.5-C5H5)Fe(CO)(PPh3)COCH:CH2]. Synthesis of an enantiomerically pure precursor for verapamil. X-ray crystal structure of [RFeRC)-{(.eta.5-C5H5)Fe(CO)(PPh3)COCH2CH2C(CN)(iPr)[3,4-C6H3(OMe)2]}