Cross-linked polystyrene-TiCl4 complex as a reusable Lewis acid catalyst for solvent-free Knoevenagel condensations of 1,3-dicarbonyl compounds with aldehydes

Cross‐linked poly(N‐vinylpyrrolidone)‐titanium tetrachloride complex: A novel stable solid TiCl4 equivalent as a recyclable polymeric Lewis acid catalyst for regioselective ring‐opening alcoholysis of epoxides

“…Also, PNVP/TiCl 4 was found to be a more effective catalyst than PS/TiCl 4 for the ring‐opening of styrene oxide with methanol under identical conditions (Table 1, entry 5) due to the higher loading of TiCl 4 per monomer unit immobilized in the PNVP carrier and better swelling in the reaction media than the PS carrier. [ 44 ] Another model ring‐opening reaction involving propylene oxide and methanol as a nucleophile using PNVP/TiCl 4 was also examined and the results are now provided in Supporting Information (Table S1).…”

“…Given the merits of catalytic performance of cross-linked polystyrene-based heterogeneous Lewis acid catalysts for a variety of organic transformations, [44][45][46][47][48][49] our goal of this study was to synthesis polymeric carrier beads containing electron-rich functional groups to enhance strong binding affinity toward small molecules, namely desired conventional metal Lewis acids and in turn the increase in the loading capacity and improve the catalytic performance of the resulting polymeric Lewis acid catalysts. Based on this strategy, we selected N-vinyl-2-pyrrolidone as a monomer for the preparation of insoluble crosslinked PNVP carrier beads containing the high pyrrolidone binding sites and their coordination complexes formation with Lewis acids.…”

“…The shelf-life period of the complex is also increased much and it did not lose its catalytic activity even after 1 year of storage and was by far more stable than that of the polystyrene-titanium tetrachloride complex catalyst, PS/TiCl 4 . [44,48]…”

“…The titanium content of the catalyst was measured by ICP, which was a value of 5.09 mmol/g while its polystyrene-supported analogue (PS/TiCl 4 ) used in our previous study had a loading capacity of 0.673 mmol/g due to the high metal binding capacity of PNVP. [44] To investigate the effect of the extent of crosslinking on capacity or the amount of titanium immobilized on PNVP support (in mmol/g), the cross-linked PNVP carrier was functionalized to the corresponding titanium tetrachloride resin by treating with a slight excess amount of TiCl 4 under identical conditions according to the procedure described in the experimental section. All the prepared complexes retained the bead form characteristic of PNVP carrier and on functionalization, the color of the resulting resin beads changes to cream, and they are stable on open air.…”

Knoevenagel Condensations Catalyzed by New Oil Shale Recyclable Catalyst at Room Temperature and Assisted by Ultrasounds Irradiations

“…Too many catalysts have been reported since the first synthesis of Knoevenagel condensation which was catalyzed by diethylamine 13 and showed then that this transformation needs a basic catalyst. In this regard, researchers developed many basic catalysts which could generate this transformation such as metal oxides such mesoporous Mg-Fe bi-metal oxides and Fly ash supported calcium oxide 14,15 , Metal-organic framework [16][17][18] , phosphates catalysts 19,20 , Dolomite 21 , alkali metal hydroxide such LiOH 21 and a limited variety of acid catalysts were also reported, we mentioned in this regard polymer-metal complex PS-TiCl 4 23 and Nano-crystalline HoCrO 4…”