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Catalyst shuttling enabled by a thermoresponsive polymeric ligand: facilitating efficient cross-couplings with continuously recyclable ppm levels of palladium.

ABSTRACT: A polymeric monophosphine ligand WePhos has been synthesized and complexed with palladium(ii) acetate [Pd(OAc)2] to generate a thermoresponsive pre-catalyst that can shuttle between water and organic phases, with the change being regulated by temperature. The structure of the polymeric ligand was confirmed with matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry and size-exclusion chromatography (SEC) analysis, as well as nuclear magnetic resonance (NMR) measurements. This polymeric metal complex enables highly efficient Pd-catalyzed cross-couplings and tandem reactions using 50 to 500 ppm palladium, and this can facilitate reactions that are tolerant to a broad spectrum of (hetero)aryl substrates and functional groups, as demonstrated with 73 examples with up to 99% isolated yields. Notably, 97% Pd remained in the aqueous phase after 10 runs of catalyst recycling experiments, as determined via inductively coupled plasma-atomic emission spectrometry (ICP-AES) measurements, indicating highly efficient catalyst transfer. Furthermore, a continuous catalyst recycling approach has been successfully developed based on flow chemistry in combination with the catalyst shuttling behavior, allowing Suzuki-Miyaura couplings to be conducted at gram-scales with as little as 10 ppm Pd loading. Given the significance of transition-metal catalyzed cross-coupling and increasing interest in sustainable chemistry, this work is an important step towards the development of a responsive catalyst, in addition to having high activity, by tuning the structures of the ligands using polymer science.

SUBMITTER: Wang E

PROVIDER: S-EPMC6844270 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Catalyst shuttling enabled by a thermoresponsive polymeric ligand: facilitating efficient cross-couplings with continuously recyclable ppm levels of palladium.

Wang Erfei E Chen Mao M

Chemical science 20190723 36

A polymeric monophosphine ligand WePhos has been synthesized and complexed with palladium(ii) acetate [Pd(OAc)<sub>2</sub>] to generate a thermoresponsive pre-catalyst that can shuttle between water and organic phases, with the change being regulated by temperature. The structure of the polymeric ligand was confirmed with matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry and size-exclusion chromatography (SEC) analysis, as well as nuclear magnetic resonance ...[more]

PMID: 31803410

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Project description:Here we report the construction and characterization of a recoverable, thermoresponsive polymer-endoglucanase bioconjugate that matches the activity of unmodified enzymes on insoluble cellulose substrates. Two copolymers exhibiting a thermoresponsive lower critical solution temperature (LCST) were created through the copolymerization of an aminooxy-bearing methacrylamide with N-isopropylacrylamide (NIPAm) or N-isopropylmethacrylamide (NIPMa). The aminooxy group provided a handle through which the LCST was adjusted through small-molecule quenching. This allowed materials with LCSTs ranging from 20.9 to 60.5 °C to be readily obtained after polymerization. The thermostable endoglucanase EGPh from the hypothermophilic Pyrococcus horikoshii was transaminated with pyridoxal-5'-phosphate to produce a ketone-bearing protein, which was then site-selectively modified through oxime linkage with benzylalkoxyamine or 5 kDa-poly(ethylene glycol)-alkoxyamine. These modified proteins showed activity comparable to the controls when assayed on an insoluble cellulosic substrate. Two polymer bioconjugates were then constructed using transaminated EGPh and the aminooxy-bearing copolymers. After 12 h, both bioconjugates produced an equivalent amount of free reducing sugars as the unmodified control using insoluble cellulose as a substrate. The recycling ability of the NIPAm copolymer-EGPh conjugate was determined through three rounds of activity, maintaining over 60% activity after two cycles of reuse and affording significantly more soluble carbohydrates than unmodified enzyme alone. When assayed on acid-pretreated Miscanthus, this bioconjugate increased the amount of reducing sugars by 2.8-fold over three rounds of activity. The synthetic strategy of this bioconjugate allows the LCST of the material to be changed readily from a common stock of copolymer and the method of attachment is applicable to a variety of proteins, enabling the same approach to be amenable to thermophile-derived cellulases or to the separation of multiple species using polymers with different recovery temperatures.

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Catalyst shuttling enabled by a thermoresponsive polymeric ligand: facilitating efficient cross-couplings with continuously recyclable ppm levels of palladium.

Publications

Catalyst shuttling enabled by a thermoresponsive polymeric ligand: facilitating efficient cross-couplings with continuously recyclable ppm levels of palladium.

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