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°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°C with quantitative yield and 60% enantiomeric excess.polymethacrylate ͉ polyisocyanate ͉ helicity ͉ polymeric ligand ͉ chiral catalyst S oluble chiral polymers may be promising ligands in asymmetric transition metal catalysis for a number of reasons. The reisolation of the mostly expensive chiral catalyst by precipitation or ultrafiltration should be easy, while all of the analytical and kinetic advantages of a reaction in homogeneous phase should be maintained. Moreover, there might be a number of beneficial effects related to the macromolecular state, for example cooperativity or chiral amplification as observed in polyisocyanates (1). These advantages may allow for the synthesis of novel catalysts with properties not achievable with micromolecular systems.The most obvious way to prepare macromolecular metal catalysts is to attach well known, catalytically active chiral components to soluble polymers. To get equal asymmetric inductions from each active site, the microenvironments of the complexed metal atoms must be uniform. This uniformity can be achieved either by attaching only one metal-binding site per polymer chain or by complexing several transition metals by a stereoregular polymer. The former strategy was realized rather successfully in the asymmetric dihydroxylation reaction with MeO-polyethylene glycolbound chiral ligands described by Bolm and Gerlach (2) and Han and Janda (3). However, the major disadvantage of this approach is the very low density of reactive centers per unit mass. A successful example for the second strategy is the application of polybinaphthol complexes as catalysts as exemplified by Pu (4). Problems associated with the latter ligands include the necessity to prepare the enantiomerically pure monomers and the question of potential counterproductive interactions of the different sources of chirality (axial chirality of the monomers and helical chirality of the polymer). Indeed, we think that for the phosphane-modified helical chiral dodecapeptides developed by Gilbertson and Wang (5) the major reason for their failure to achieve good enantioselectivities in asymmetric hydrogenation r...

A practical, one-pot synthesis of enantiopure unsymmetrical salen ligands is described, using a 1:1:1 molar ratio of a chiral diamine and two different salicylaldehydes. The new synthetic protocol can be readily performed in good yields (60-85%) on a multigram scale with good tolerance toward various functional groups.

We report a modular approach toward polymer-supported, metalated, salen catalysts. This strategy is based on the synthesis of monofunctionalized Mn- and Co-salen complexes attached to a norbornene monomer via a stable phenylene-acetylene linker. The resulting functionalized monomers can be polymerized in a controlled fashion using ring-opening metathesis polymerization. This polymerization method allows for the synthesis of copolymers, resulting in an unprecedented control over the catalyst density and catalytic-site isolation. The obtained polymeric manganese and cobalt complexes were successfully used as supported catalysts for the asymmetric epoxidation of olefins and the hydrolytic kinetic resolution of epoxides. All polymeric catalysts showed outstanding catalytic activities and selectivities comparable to the original catalysts reported by Jacobsen. Moreover, the copolymer-supported catalysts are more active and selective than their homopolymer analogues, providing further proof that catalyst density and site isolation are key toward highly active and selective supported salen catalysts.

No other sources of chirality except its helicity are present in the polymeric ligand shown, which was prepared by helix‐sense‐selective polymerization. Palladium complexes of this ligand catalyze allylic substitution reactions. The resulting asymmetric induction is a direct and sole consequence of the uniform helicity of the polymeric ligand.