Molecularly Imprinted Polymers for (Thio)urea Organocatalyst Recovery and Recycling

The strong binding affinity of carboxylate-based ion pair monomers toward ureas and thioureas (>105 L mol–1 in DMSO-d6) has been utilized to prepare organocatalyst-selective molecularly imprinted polymers for the first time. These polymers exhibited exceptionally strong binding for the organocatalyst targets and were applied in the reversible capture of Schreiner’s urea and thiourea from reaction mixtures. Recycling and reuse of these precious homogeneous catalysts is achieved using rapid and straightforward solid-phase extraction protocols. Catalyst recoveries of up to 98% from Diels–Alder and Baylis–Hillman reactions are demonstrated, while the polymers themselves are stable for at least 100 extraction cycles without loss of performance.