The compound [Pd(Me-DUPHOS)(MeCN)2](BF4)2, 1[Me-DUPHOS = 1,2-bis(2,5-dimethylphospholano) benzene], has been found to be an effective catalyst for the highly enantioselective, alternating copolymerization of aliphatic α-olefins with carbon monoxide to form optically active, isotactic polymers. The α-olefin-carbon monoxide copolymers, as synthesized in CH3NO2/CH3OH, had a mixture of 1,4-ketone and spiroketal repeating units in the backbone. The interchange between 1,4-keto and spiroketal units was observed even in the absence of any added metal catalyst. The temperature dependence of the molar optical rotation of the isotactic pure poly(1,4-ketone)s indicated that the chirality of the copolymers was due to the presence of stereogenic tertiary carbons in the polymer backbone rather than due to polymer conformation. The degree of enantioselectivity in the formation of chiral, isotactic propylene—carbon monoxide copolymer was found to be >90% (as determined by NMR spectroscopy using a chiral NMR shift reagent). The isotactic α-olefin—carbon monoxide copolymers serve as excellent starting materials for the synthesis of other classes of chiral polymers. For example, the complete reduction of the propylene—carbon monoxide copolymer resulted in the formation of a novel, optically active poly(1,4-alcohol). Finally, 1 was also found to be a catalyst for the novel alternating isomerization cooligomerization of 2-butene with carbon monoxide to form optically active, isotactic poly(1,5-ketone).
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry