Imines resin supported catalysts

At a loading as low as 1 mol%, 10b promoted the hydrocyanation of A-allyl or -benzyl imines derived from aromatic and aliphatic aldehydes and of some ketones in very high yield and almost complete stereoselectivity (see Scheme 2). It is interesting to note that the soluble and the resin-bound catalysts performed equally well. Recovery and recycling of the supported catalyst was shown to occur without any erosion of chemical or stereochemical efficiency over ten reaction cycles. 

The isolation of product is usually possible after evaporation of the solvent and extraction with hexane, ether, or toluene. Supported versions, for example on polystyrene grafted with PPh2 groups, have proved unsatisfactory because the rate of deactivation is greatly enhanced under these conditions [37]. Asymmetric versions exist, but the ee-values tend to be lower than in the Rh series [38]. With acid to neutralize the basic N lone pair, imine reduction is fast. Should it be necessary to remove the catalyst from solutions in order to isolate a strictly metal-free product, a resin containing a thiol group should prove satisfactory. A thiol group in the substrate deactivates the catalyst, however. 

Shibasaki et al. developed a polymer-supported bifunctional catalyst (33) in which aluminum was complexed to a chiral binaphtyl derivative containing also two Lewis basic phosphine oxide-functionahties. The binaphtyl unit was attached via a non-coordinating alkenyl Hnker to the Janda Jel-polymer, a polystyrene resin containing flexible tetrahydrofuran-derived cross-Hnkers and showing better swelling properties than Merifield resins (Scheme 4.19) [105]. Catalyst (33) was employed in the enantioselective Strecker-type synthesis of imines with TMSCN. 

Polymer-supported equivalents of the widely used organic base 4-(dimethylamino)pyridine (DMAP) were soon developed, but many of their reported applications are as a stoichiometric base. Resin 37 (Scheme 10.10), containing a polyethylene imine) matrix was the first supported system to be prepared. Those materials were more efficient catalysts than DMAP itself, under the same conditions, for the hydrolysis of p-riilropheriyl esters in aqueous solution [175, 176],... 

Portnoy focused his attention on the immobilization of PyBox ligands [153], The polymer-supported PyBox 240 were prepared in five steps from the Wang trichloroacetamidate resin (Scheme 96). The supported-ligands 240 were allowed to react with copper (1) triflate for 24h to afford the corresponding catalysts 241. These catalysts were then used in the first heterogeneous catalyzed addition of phenylacetylene to imine. 

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