Self-Assembled Complexes of Non-cross-linked Amphiphilic Polymeric Ligands with Inorganic Species: Highly Active and Reusable Solid-Phase Polymeric Catalysts

Abstract

IntroductionDevelopment of immobilized and insoluble metal catalysts is of great interest in recent organic chemistry. [1][2][3][4][5][6][7][8][9] The simple recovery of catalysts by filtration and their reuses resulted in enhancing the economical evaluation of the reaction. At the same time, there is a prospect that the environmental pollution caused by residual metals in the waste fluid will be decreased. Although a great deal of effort has been made to carry out such ideal reactions using immobilized metal catalysts, what seems to be lacking is the efficiency of the catalytic systems. It is obvious that the heterogeneous catalytic systems exhibit generally lower activity than the homogeneous ones. Besides, it is expected that the activity of the catalysts decreases gradually in the recycled systems because the metal species leaches away from their supports. Taking these into consideration, we decided to concentrate on developing insoluble metal catalysts which are highly active and stable. We designed that they were still effective in the use of ppm mol eq, and in the recycled use of many times in any reaction media. To achieve the challenging theme, we have focused on the amphiphilic insoluble catalysts based on a novel concept (Chart 1).Over the past few decades, a considerable numbers of study have been made on solid-phase catalysts which were immobilized with cross-linked polystyrene resins, silica gels or metals. These catalytic systems, however, generally resulted in lower catalytic activity compared with their soluble counterparts, and were often obliged to use hazardous chlorohydrocarbon solvents. [10][11][12][13][14][15] Besides, reuse of these catalysts was often difficult owing to the gradual decline of the catalytic activity. These problems made them less practical.In traditional triphase catalysts, as I have mentioned before, a catalytic species was anchored to a linker that was immobilized to a polymer resin or silica gel (Chart 1, above). In July 2005Chem. Pharm. Bull. 53(7) 723-739 (2005)

Development of dipyridine‐based coordinative polymers for reusable heterogeneous catalysts

“…The electron‐donating substituent on bromobenzene led to a lower catalytic efficiency (Table , Entry 6) and reversely, the electron‐withdrawing group raised the conversion and TON of the reaction (Table , Entries 7 and 8), which matched the trend reported in the literature . The TON could approach a higher value of 116 in the reaction of 4‐tolyboronic acid and iodobenzene with a shorter reaction time (Table , Entry 9) . However, the leakage of Pd species was significant during the recycling process and thus we tried to improve Catalyst 2 by the modification of the polymer backbone.…”

“…The Pd leakage was undetectable and the yield was constantly higher than 94% after 5 times recycling. In the literature, the range of TON for heterogeneous catalysis of Suzuki‐Miyaura coupling is generally around 30 to 20,000 . Although poly(MVPhDPy‐ co ‐NIPAM)‐Pd(OAc) 2 showed a moderate catalytic activity, the ease of catalyst recycle and the little leakage of metal ions along with the versatility of polymeric platform that could coordinate with different metal ions to catalyze varied reactions provide this copolymer a great potential for future applications.…”

Development and Application of New Oxidation Systems Utilizing Oxometalate Catalysts

“…[214][215][216][217][218][219][220] Previously, our group found that an assembled complex of non-cross-linked PNIPAAm copolymer ligands and inorganic salts affords insoluble solids in water and possesses functions as a triphase catalyst. [221][222][223][224] To design a new oxometalate catalyzed oxidation system based on thermomorphic property of PNIPAAm, a dye-labeled catalyst 11b comprising a phosphotungstate anion, a PNIPAAm polymer chain, and a Disperse Red moiety was synthesized (Chart 7). 224) Interestingly, this model catalyst 11b could cause drastic mode transfer at several temperatures in aqueous medium; when 11b is used together with water and the organic substrates it is insoluble in both phase at room temperature.…”

Tightly Convoluted Polymeric Phosphotungstate Catalyst: An Oxidative Cyclization of Alkenols and Alkenoic Acids

“…The development of immobilized catalysts exhibiting high aquacatalytic activity and recyclability has become an important topic in organic chemistry today. , We have developed amphiphilic polymer resin-supported transition-metal complexes and nanoparticles that catalyze various organic transformations in water under heterogeneous conditions. − Recently, we have also presented a novel self-assembling protocol for the preparation of solid-phase catalysts where metal species served as cross-linkers of non-cross-linked polymeric ligands as well as catalytically active centers. , Thus, for example, an ionically cross-linked polymeric phosphotungstate catalyst PWAA was prepared via salt formation of PW 12 O 40 3- with poly{{[3-(acryolylamino)propyl]dodecyldimethylammonium nitrate}- co -( N - isopropylacrylamide) 12 }, a main chain of poly( N -isopropylacrylamide) bearing branched ammonium cation parts (Figure , top) . The polymeric phosphotungstate PWAA catalyzed the oxidation of alkenes, amines, and sulfides; however, it could not be sufficiently recycled presumably due to its physical fragility.…”