Asymmetric catalytic synthesis of polyketones and polycarbonates
K. Nozaki
Department of Chemistry and Biotechnology, Graduate
School of Engineering,
The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Abstract: Two examples are presented for the synthesis of optically
active polymers with main-chain chirality from achiral monomers using
chiral metal-complexes as catalysts. Asymmetric alternating copolymerization
of α-olefins with carbon monoxide provided optically active polyketones
when catalyzed by an (R,S)-BINAPHOS-Pd complex. From propene
and CO, highly isotactic polyketone with high enantioselectivity (>97
% like diad and >95 % ee). Spectroscopic and theoretical studies revealed
that the olefin insertion is the key step for the enantiofacial selection
and that this step takes place at cis to the phosphine part of (R,S)-BINAPHOS.
The catalyst is applicable not only to propene/CO but also to styrene/CO,
which enabled the first asymmetric terpolymerization of propene/styrene/CO.
The catalyst tolerates funational groups such as fluorocarbons and a
nitrile group so that they can be incorporated in the side chain. Optically
active polycarbonate was also synthesized by the alternating copolymerization
of cyclohexene oxide with carbon dioxide via the desymmetrization of
the meso-epoxide. Dinuclei zinc species prepared from diethylzinc,
ethanol, and α,α'-diphenylprolinol, was revealed to be the
real active species.
*Plenary and invited lectures presented at the 12th
International Symposium on Organometallic Chemistry Directed Towards
Organic Synthesis (OMCOS-12), Toronto, Ontario, Canada, 6-10 July 2003.
Other lectures are published in this issue, pp.
453-695.
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