Asymmetric hydrovinylation of styrene applying cationic allyl palladium complexes of a P-chiral ligand

Cationic allyl palladium complexes of the diasteriomerically pure P-chiral ligand tert-butyl(menthyl-O)phenylphosphinite 1 were prepared from [(¿3-C3H5)PdI]2 and [(¿3-C3H5)Pd(cod)]X. Ligand 1 and the complex [(¿3-C3H5)PdI(1)] 9 were characterized by X-ray crystallography. The absolute configuration at the phosphorus center of 1 was determined to be (S) for the (-)-menthol derivative. Crystals are orthorombic, space group P212121, a=8.505(3) Å, b=10.82(1) Å, c=23.297(3) Å, V=2144(2) Å3. Complex 9 shows distorted square planar geometry. Crystals are trigonal, space group P32, a=13.980(5) Å, c=11.292(3) Å, V=1911(2) Å3. Asymmetric codimerization of styrene and ethylene was successfully applied. High enantioselectivities of up to 86% ee have been obtained at room temperature. The codimer 3-phenylbut-1-ene (3PB1) was formed in high selectivity (up to 96%) with only small amounts of the isomerization products E- and Z-2-phenylbut-2-ene. By addition of various coordinating solvents, the catalyst system was efficiently stabilized. Variation of the complex counter anion had significant effect on enantioselectivity.