Biomimetic catalysis with an immobilised chiral rhodium(III) complex

An organometallic transition state analogue for the asymmetric reduction of acetophenone with a Cp*Rh complex has been synthesised and structurally ch aracterised (3). This complex has a chiral N,N'-chelate Ligand with a styre ne side chain to allow its incorporation into organic polymers. The remaini ng coordination site is occupied by a methyl-phenylphosphinato ligand. This ligand acts asa pseudosubstrate which mimics acetophenone. The conformatio n and configuration of 3 in the crystal are in excellent agreement with the postulated transition structure. Following the protocol of molecular impri nting, complex 3 was co-polymerised with ethylene glycol dimethacrylate in the presence of a porogen. The resulting polymer P3 was ground and sieved a nd the phosphinato ligand was substituted with a chloro ligand to generate a shape-selective cavity in proximity to the catalytically active metal cen tre. When tested for its ability to catalyse the reduction of acetophenone and related substrates the imprinted polymer P3 showed a significantly high er activity than a control polymer P2 without a cavity. Excellent enantiose lectivities (up to 95% ee) were obtained, with the catalyst P3 being more s elective than the respective control catalyst P2 (Delta ee = 2-9%). Competi tion experiments with acetophenone and a second co-substrate have revealed that the cavity generated with the phosphinato ligand is specific for aceto phenone.