Helically chiral polymers: a class of ligands for asymmetric catalysis.
Helically chiral polymers from achiral monomers containing N and P atoms have been shown to be ligands for transition metals such as Pd and Rh. The Rh complex of the phosphane-containing polyisocyanate p(18-co-17) was an active albeit hardly enantioselective catalyst in the asymmetric hydrogenation of the dehydro amino acid N-acetamidocinnamic acid (15% enantiomeric excess). The most active catalyst obtained until now was the Pd-complexed polymethacrylate Pd-p12, which catalyzes the allylic substitution reaction of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate even at -20 degrees C in quantitative yield, although again the enantioselectivity was unsatisfactory. The most successful application of a helically chiral polymer in asymmetric catalysis with respect to both reactivity and enantioselectivity is the polymethacrylate p(5-co-8). Its palladium complex catalyzes the above-mentioned reaction at 0 degrees C with quantitative yield and 60% enantiomeric excess.
Reggelin
Michael
M
Institut für Organische Chemie, Technische Universität Darmstadt, Petersenstrasse 22, D-64287 Darmstadt, Germany. re@punk.oc.chemie.tu-darmstadt.de
Doerr
Sebastian
S
Klussmann
Martin
M
Schultz
Melanie
M
Holbach
Michael
M