Enantioface discriminating carbonylations of styrene with cationic palladium(II) catalyst precursors

The enantioface discriminating copolymerization of styrene with carbon monoxide using palladium complexes [(L∧L′)Pd(S)2](X)2 of the C1-symmetric ligands (S,S)-2-[2-(diphenylphosphino)phenyl]-3-phenyl-4-methoxymethyl-4,5-dihydrooxazole or (S,S)-2-(2-pyridyl)-3-phenyl-4-methoxymethyl-4,5-dihydrooxazole gives highly isotactic or syndiotactic poly(1-oxo-2-phenyl-1,3-propanediyl), respectively. With the former catalytic system, efficient enantioface discrimination takes place only after the first insertion step and is only slightly influenced by the growing chain, as shown by the chiroptical properties of terpolymers with ethene. Similar terpolymerization experiments with the latter catalyst precursor show that the fairly good enantioface discrimination due to the catalyst is in opposition to the influence of the chirality of the growing chain. The latter effect predominates resulting in the formation of the overwhelmingly syndiotactic copolymer.