A Concept of Supported Amino Acid Ionic Liquids and Their Application in Metal Scavenging and Heterogeneous Catalysis

Abstract

Novel supported task-specific ionic liquids have been developed for the first time via the ionic-pair coupling of imidazolium cation of the modified polystyrene support with L-proline. The materials have shown an efficient metal scavenging ability (e.g., CuI, Pd(OAc)2, Pd0, and IrCl3) without the aid of a nonimmobilized ionic liquid, which relies on the highly synergistic effect of the coordination with the nitrogen atom and the COO- group of the L-proline moiety, electrostatic forces, and steric protection. The resulting metal-soaked supported ionic liquids can be used as efficient heterogeneous catalysts. These materials have been investigated in the CuI-catalyzed N-arylation of nitrogen-containing heterocycles and exhibit much higher catalytic activity and a more extensive structural range of aryl and heteroaryl halides than those exhibited by free L-proline in combination with CuI both in the ionic liquid ([BMIM][BF4]) and in the corresponding homogeneous reaction conditions. The CuI-soaked catalyst 4a-2 can be recycled for nine runs at least without any considerable loss of activity. To the best of our knowledge, our catalytic process is among the most efficient approaches to the N-arylation of imidazoles with aryl halides so far reported. Furthermore, the Pd-soaked material 4a-2 also shows higher catalytic activity in the solvent-free hydrogenation of styrene to ethylbenzene. This new concept is generally applicable and may easily be extended to other supported task-specific ionic liquids.

Reduction Reactions in Green Solvents: Water, Supercritical Carbon Dioxide, and Ionic Liquids

“…Examples of hydrogenation of alkenes have been reported with a metal catalyst immobilized on sepiolite, [99] alumina, [100] polyaniline, [101] silica gel, [102] and in polymeric backbones (Figure 2). [103] Similar to supercritical fluids, there are very few examples of enzymatic reactions in ionic liquids. Howarth and co-workers reported the reduction of several ketones using immobilized baker's yeast in 10:1 bmimPF 6 /H 2 O mixture.…”

Amphiphilic Hybrid π‐Conjugated Polymers Containing Polyhedral Oligomeric Silsesquioxanes

“…Presumably, in the case of 1b, the deprotonation at the C2 position of the imidazolium nucleus can generate N-heterocyclic carbenes because of the relatively high acidity (pK a ¼ 21-23) of the H2 hydrogen, and may further result in the formation of metal-carbene complexes and subsequent insoluble polymer networks. [12] In the case of 1c, although the 2-position of the imidazolium ring is protected by a methyl group, the higher packing ability of the dodecyloxy groups could cause insoluble aggregate formation. The number-average molecular weights of P1 and P2 measured by GPC were 4 500 and 7 000 g Á mol À1 , respectively, which were in good agreement with the molecular weights determined by 1 H NMR spectroscopy ( Figure S1).…”

Hydrogenation in Ionic Liquids

“…The authors describe formation of solvent cages in IL systems as the reason for enantioselectivity promotion with the SILCs. Chen et al [127] discovered efficient metal scavenging abilities of their task-specific ILs (TSILs) supported on a polystyrene backbone. The materials were formed by the ionic pair coupling of the imidazolium cation tethered to a polystyrene support with L-proline.…”