Abstract
A new polymeric NHC carrier was synthesized by sequential supramolecular self-assembly and copper-catalyzed azide-alkyne cycloaddition (CuAAC) of amphiphilic imidazolium calix[4]arenes with octyl lipophilic fragments. Obtained polytriazole-imidazolium particles were found as monodisperse submicron particles, with the average diameter of 236 ± 34 nm and average molecular weight of 1380 ± 96 kDa. Successful CuAAC polymerization has been proved using IR spectroscopy and high-resolution ESI mass spectrometry. Polymeric particles, as well as aggregates made from precursor macrocycles, were decorated by Pd clusters (2 nm) for further catalytic investigations. Pd nanoclusters, supported on the polymeric surface, were found highly catalytically active in the model reduction of p-nitrophenol, giving reaction rates an order of magnitude higher compared to literature examples. The reaction was recycled using the same catalyst five times without any loss of activity.
Highlights
During the last few decades, N-heterocyclic carbene (NHC) ligands have attracted considerable attention, owing to their high stability and outstanding applications in homogeneous catalysis [1,2,3]
Amongst N-heterocyclic carbenes, polytopic ligands featuring more than one NHC unit are of high demand, as they impact the stability of the final metal complex, owing to their chelating abilities [8,9]
[15], we proposed a new approach to the formation of polymeric NHC carriers based on sequential supramolecular self-assembly of amphiphilic calix[4]arenes containing azidoalkyl/alkynyl fragments on the polar region of macrocycles into aggregates in an aqueous solution, followed by foregoing cross-linking of macrocycles using a coppercatalyzed azide-alkyne cycloaddition (CuAAC) reaction (Scheme 1)
Summary
During the last few decades, N-heterocyclic carbene (NHC) ligands have attracted considerable attention, owing to their high stability and outstanding applications in homogeneous catalysis [1,2,3]. [15], we proposed a new approach to the formation of polymeric NHC carriers based on sequential supramolecular self-assembly of amphiphilic calix[4]arenes containing azidoalkyl/alkynyl fragments on the polar region of macrocycles into aggregates in an aqueous solution, followed by foregoing cross-linking of macrocycles using a coppercatalyzed azide-alkyne cycloaddition (CuAAC) reaction (Scheme 1). The data obtained agree with those previously obtained by the MALDI method: similar structures cleave off imidazolium fragments, converting to the corresponding quinone methides [15]
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