Co- and terpolymers of N-isopropylacrylamide exhibit inverse temperature solubility in water with the polymer's lower critical solution temperature (LCST) being dependent on the polymer's microstructure and the concentration of salt in the water solvent. This solubility behavior has been used to prepare “smart” recoverable homogeneous catalysts and substrates. These catalysts' activity reversibly turns first off and then on as the temperature is first raised and then lowered due to changes in the polymer support's solubility. Such catalysts can be recovered by heating the aqueous solution or by adding brine. Catalysts prepared include both phosphine-ligated transition metal catalysts and acid catalysts. The transition metal catalysts are active in alkene hydrogenation, C−C coupling, and allylic substitution reactions. The acid catalysts are active in acetal hydrolysis. Substrates can be attached to these polymers and their activity likewise can be turned off and on by heating or cooling. Substrate activity on such supports can equal that of a low molecular weight analogue. NMR spectroscopic studies show that a vinyl group bound to PNIPAM has peaks whose line widths in 1H NMR spectroscopy are like those of a low molecular weight compound when a nine-carbon tether chain is used to attach the vinyl group to PNIPAM.

A new pincer-type SCS ligand containing Pd(II) is a simple, robust catalyst for Heck chemistry using a variety of alkene acceptors and aryl iodides. It is less active with aryl bromides. While certain palladium(II) species insert slowly into the aryl C−H bond of an unsubstituted version of this ligand, the introduction of activating groups into the 5 position of the aromatic ring readily allows quantitative metal insertion. These ligands were synthesized and attached to soluble polymers by simple modification of inexpensive starting materials. For example, both 5-oxy and 5-amido SCS ligands were successfully appended to 5000 M n poly(ethylene glycol) via ether or amide linkages, respectively. Both the 5-oxo and 5-amido complexes are active as Heck catalysts in DMF solution in air. The PEG-bound 5-amido-SCS−Pd complex was recycled via solvent precipitation three times with no observed catalyst deactivation. While the 5-amido-SCS−Pd complexes are very robust, their 5-oxo counterparts decompose slowly under certain conditions. These SCS catalysts are analogous to PCP-type catalysts previously reported in the literature but avoid the requirement of an air-sensitive phosphine synthesis.

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