Salen dendrimer-cored

Seebach introduced a novel concept for the immobilization of chiral ligands in PS. The ligand of choice was placed in the core of a styryl-substituted dendrimer 134, which was copolymerized with styrene under suspension polymerization conditions to give the polymeric chiral ligand 135 [74]. The corresponding polymeric (salen) Mn complexes were used to catalyze the enantioselective epoxidation of alkene (Scheme 3.38), with the polymeric complexes being recycled ten times... 

Figure 4.42 Chiral BINOL- and salen-cored dendrimers with styryl groups located at the periphery.

Styryl-terminated Frechet-type dendrimers have been introduced as novel polymer crosslinkers by Seebach et al. [43-45]. They are constituted of four to 16 peripheral styryl units attached to aryl end branches of dendritic TADDOL, BINOL or Salen ligands and were copolymerised with styrene by suspension polymerisation. The catalytic performance of the polymer-bound catalyst was identical to that of the homogeneous analogues however, the supported catalysts could be used in many consecutive catalytic runs with only small loss in catalytic activity. A major drawback of fixing the catalytic unit in the core of the crosslinker is the poor loading capacity of the final polymer (0.13-0.20 mmol g 0> especially when high amounts of catalysts (10-20 mol%) are needed. 

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