Nanofiltration for Homogeneous Catalysis Separation:  Soluble Polymer-Supported Palladium Catalysts for Heck, Sonogashira, and Suzuki Coupling of Aryl Halides

Abstract

The anionic polymerization of 4-methylstyrene results in a linear poly(4-methylstyrene), whose substoichiometric bromination with Br 2 converts a portion of 5-18% of the -CH 3 units into -CH 2 Br groups, which were then reacted with (1-Ad) 2 PH to synthesize a polymer loaded with sterically demanding and electron-rich -CH 2 P(1-Ad) 2 groups as the respective air-stable phosphonium salt. Palladium complexes with the phosphinated polymer are efficient catalysts for carbon-carbon coupling reactions of the Sonogashira, Suzuki, and Heck type with aryl chlorides and bromides. The molecular weight of the respective phosphines in the range of 5-35 kDa does not have a significant effect on the catalytic performance. Such polymer-enlarged catalysts are suitable for separation over a solventresistant nanofiltration membrane composed of a dense poly(dimethylsiloxane) (PDMS) layer cast on a porous sublayer of poly(acrylonitrile) (PAN). The membrane displays virtually quantitative retention of the polymeric catalyst; furthermore palladium could not be found in the permeate; TXRF and spectrophotometric determinations are indicative of >99.95% retention of the catalyst. The activity of the catalyst retained in the retentate is almost unchanged, as shown by the high (typically >90%) and almost constant yields of the coupling reactions as well as by the constant turnover frequencies of the catalysts following the membrane separation experiments during up to nine cycles of Sonogashira and Suzuki reactions. For the Heck coupling the used polar aprotic solvents best suited for the catalytic reaction lead to rapid deterioration of the membranes tested.

Synthesis and determination of pKa values of new enantiopure pyridino- and piperidino-18-crown-6 ethers

“…heneicosa -1(21),17,19-triene-2,16-dione (S,S)-6. Crown ether (S,S)-6 was prepared as described above in the General procedure starting from methoxy-substituted carboxylic acid (19) (287.8 mg, 1.46 mmol), thionyl chloride (3.60 mL, 49.66 mmol), chiral diamine (S,S)-10 (328.3 mg, 1.46 mmol), triethylamine (0.55 mL, 3.95 mmol) using toluene (280 mL). The crude product was purified by column chromatography on neutral aluminium oxide using EtOH-toluene 1:180 mixture as an eluent to yield (S,S)-6 (75.0 mg, 11%) as a yellowish brown oil.…”

“…[14][15][16] OSN was suggested for the separation of Williamson etherification reaction mixtures 17,18 and homogeneous catalyst recovery. 19 Schaepertoens et al recently proposed a three-stage membrane cascade for the purification of dibenzo-18-crown-6 ether and in situ solvent recycle. 20 This article presents a preliminary study of the potential of OSN in the purification and recovery of pyridino-and piperidino-crown ether based catalysts.…”

Interests and challenges of organic solvent nanofiltration for sustainable chemistry: the case of homogeneous catalysis of metathesis

“…Various studies at laboratory scale have been published dealing with the retention of homogeneous organometallic catalysts and recycling by organic nanofiltration (OSN) most often in methanol or other polar solvents: CoJacobsen (4 cycles) [11], Heck (5 cycles) and Suzuki (10 cycles) reaction catalysts [12,13] and more rarely in an aromatic solvent (toluene) as for Hoveyda catalysts for the olefin metathesis [14]. However, to be widely used on an industrial scale, the NF in organic medium faces several challenges.…”

Aspects of Immobilisation of Catalysts on Polymeric Supports

“…[272][273][274][275] Sometimes, a trade-off exists when the best conditions for catalysis are incompatible with those for filtration. [276,277] The introduction of high-throughput membrane testing [278] and combinatorial synthesis techniques [279] for SRNF membranes might speed up developments. SRNF has recently been coupled to nanocolloid-catalysed reactions to realise the first effi-cient recycling of this type of pseudo-homogeneous catalysts for which filtration remained problematic.…”