Air-stable SCS palladacycles that can be used to promote C À C coupling chemistry were studied mechanistically. Using a small library of electronically varied SCS ligands, a collection of palladacycles was synthesized. Kinetic studies showed that these complexes all had induction periods, induction periods that were effected by concentration of substrates, products and trace impurities. Hammet correlations showed that electronically diverse palladacycles had identical 1 values, values that suggested that aryl halide electrophilic addition to a Pd species was not the rate-determining step. Phosphine addition experiments led to increased reactivity of the starting palladacycles, possibly by trapping an in situ generated Pd(0) species. Studies that examined reactivity in biphasic thermomorphic reactions showed residual activity in phases that do not contain polymer-bound palladacycle and provided convincing evidence that palladacycles are not the actual catalyst. Poisoning experiments using mercury metal to test for the presence of a Pd colloid were very effective with low molecular weight palladacycles, completely suppressing Heck chemistry. Similar studies with polymer-bound palladacycles showed mercury poisoning too. However, since so little decomposition of the palladacycle occurred, the polymer-bound palladacycle could still be recycled multiple times. However, mercury poisoned subsequent cycles of the experiment too. The conclusion is that SCS palladacycles are actually reservoirs of a catalytically active but ill-defined form of palladium(0).

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Ion‐exchange polymers with “on”/“off” solubility can be prepared from N‐isopropylacrylamide (PNIPAM) copolymers that incorporate hydroxamic acid ligands. Such complexing agents quantitatively remove trace amounts of FeIII from aqueous solutions (vial 1) by precipitating the metal – polymer complex on heating (suspension in vial 2). Physical separation of the insoluble polymer leaves a metal‐free solution (vial 3). Similar fluorous phase‐soluble hydroxamic acid derivatives of fluoroacrylate polymers remove FeIII ions from organic solutions by liquid/liquid phase separation.

A new strategy for carrying out reactions with a soluble polymer-bound reagent or catalyst is described. In this latent biphasic process, a solvent mixture at the cusp of immiscibility is prepared and used to carry out a reaction under homogeneous conditions. Then, after the reaction is complete, this mixture is perturbed by the addition of solvent or some other perturbing agent to produce a biphasic mixture. The product-containing phase is then separated under liquid/liquid conditions from the polymer-containing phase. The generality of this process is demonstrated using both dye-labeled polymers as surrogates for polymer-bound catalysts and with various polymer-bound organic and transition metal catalysts or reagents. In cases where a polymeric catalyst is used, the addition of fresh solvent and substrate reforms the original mixture allowing facile reuse of the catalyst.

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