Optically active transition-metal complexes. 9. A general stereoselective route to alpha-chiral (R)-tricarbonyl(eta(6)-ethylbenzene)chromium complexes. Novel organometallic phosphine catalysts for the asymmetric hydrovinylation reaction

Treatment of (R)-[{alpha-(dimethylamino)ethyl}-eta(6)-benzene]Cr(CO)(3) wit h esters of chloroformic acid leads to stereoselective substitution of the dimethylamino group for a chloro substituent. The reaction can be extended to systems in which the chromium arena complex, after metalation, is diaste reoselectively substituted in the ortho position with carbon and silicon el ectrophiles to generate planar chirality; The! chloro group in turn can be replaced stereoselectively for various phosphorus, nitrogen, and oxygen nuc leophiles. Both substitution reactions ill the benzylic position proceed vi a retention of configuration. The addition of cyanide is not stereospecific . The phosphine derivatives are efficient catalysts for the enantioselectiv e hydrovinylation of styrene to 3-phenyl-1-butene. X-ray crystal structures establish the absolute configuration of (R)-[(alpha-chloroethyl)eta(6)-ben zene]Cr(CO)(3), (R)-[{alpha-(diphenylphosphanyl)ethyl}-eta(6)-benze ne]Cr(C O)(3), and (pS,S)-[1-(alpha-cyanoethyl)-2-methyl-eta(6)-benzene]Cr(CO)(3).