Effect of Chiral Cavities Associated with Molecularly Imprinted Platinum Centers on the Selectivity of Ligand-Exchange Reactions at Platinum

The metallomonomer (vinyl dppe)Pt[(R)-Bu2BINOL] (1) was copolymerized with ethylene glycol dimethacrylate to produce the molecularly imprinted polymer (MIP) P1. The chiral imprinting ligand (R)-Bu2BINOL was removed from P1 by treatment with HCl or an excess of α,α,α-trifluoro-m-cresol, BINOL, or Br2BINOL, giving polymers P2−P5. The amount of imprinting ligand released from P1 varied inversely with the steric bulk of the cleaving agent, indicating that a distribution of Pt sites with different accessibilities exists in the MIP. Exposure of P3 (containing Pt(OAr)2 centers surrounded by (R)-Bu2BINOL-shaped cavities) to rac-BINOL, an imprinting ligand analogue, led to preferential rebinding of the imprinted enantiomer via ligand exchange. Both aggregate selectivity and extent of reaction (percent of the total Pt sites in the MIP that participated in rebinding) increased with rebinding time and with temperature, up to 69% ee and 58% Pt sites rebound, respectively. A positive linear correlation between selectiv...