Olefin complexes containing prochiral

Circular Dichroism Spectra of Square Planar Complexes Containing Prochiral Olefins and Their Stereoselective Olefin Exchange... 

Several workers have studied platinum(II) complexes of olefins containing chiral amine or amino-acid ligands. Panunzi(9) observed stereoselectivity in the reaction between cis-(S - a-methylbenzylamine)dichloroplatinum (II) and trans-2-butene with the major diastereomer formed to the extent of 70% of total complex. More recently (10), it has been shown that the replacement of coordinated trans-2-butene by free olefin in (S-prolinato) dichloroplatinum (II) complexes takes place more easily with retention than with inversion. Addition of a large excess of trans-2-butene to solutions of the corresponding ethylene complexes produced first an increase and then a gradual decrease in their circular dichroism. The kinetic stereoselectivity in this reaction (that is, the differing reaction rates of the two prochiral faces of trans-but-2-ene) was 3 1, but at equilibrium the ratio of major and minor diastereomers was 64 36 in the cis-isomer and 59 41 in the trans-isomer. 

In the early 1980s, Kaminsky and Sinn discovered an efficient way to activate homogeneous metallocene catalysts with methylaluminoxane (MAO). Titanocene and zirconocene complexes activated with MAO exhibited very high activity for ethylene polymerization these early systems, however, still had low activity for propylene polymerization and formed atactic polypropylene [5]. Met-allocene/MAO systems containing stereospecific ligands could be used to catalyze the polymerization of prochiral olefins (a-olefins) through the use of catalysts with well-defined active sites [6]. Later, Brintzinger [7] and Ewen... 

Like reactions of many other prochiral olefins, the geometry of the enamine can affect selectivity. Thus, cyclic enamides that contain one geometry react with high selectivities (Equation 15.36). Alternatively, catalysts that react with both isomers with high selectivity for the same enantiomer can be developed. Equation 15.37 shows that the rhodium-DuanPhos complex catalyzes the hydrogenation of an /Z mixture of isomeric enamides with high enantioselectivity. ... 

---