Effects of Thickness and Grafting Density on the Activity of Polymer‐Brush‐Immobilized Tris(triazolyl) Copper(I) Catalysts

Abstract

We report herein the application of polymer brushes for the immobilization of tris[(1,2,3‐triazolyl)methyl]amine CuCl catalysts. Well‐defined catalytic brushes were prepared through grafting‐from and postpolymerization modification approaches on Si surfaces and characterized by X‐ray reflectivity, X‐ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry. Hairy catalysts of varying thickness and grafting density were investigated in a model CuI‐catalyzed azide–alkyne cycloaddition reaction and showed remarkable activity at loadings as low as 0.02 mol % as a result of the unique catalytic site density and nuclearity found in the brush. We demonstrate that thickness and grafting density parameters can be adjusted to maximize catalytic activity along the brush thickness.

Sequence and Surface Confinement Direct Cooperativity in Catalytic Precision Oligomers

“…Detailed analysis of C, N, and Cu high resolution XPS regions did not show significant differences between the two grafted oligomers to account for specific conformations on the surface; yet, Cu 2p 1/2 and Cu 2p 3/2 peaks at ca. 952.2 and 932.4 eV, respectively, confirmed the presence of Cu I species in each catalyst . ICP-AES analysis of 3 and 4 gave close Cu contents values of 0.14 and 0.12 mmol/g, respectively, indicating partial but equivalent Cu complexation for both catalysts (Table S3); it is remarkable to notice that the Cu center in 3 and 4 is the copper used for the CuAAC-grafting itself, hence reducing the preparation of the supported hybrid multifunctional catalysts to one single step from azide silica .…”

“…952.2 and 932.4 eV, respectively, confirmed the presence of Cu I species in each catalyst. 18 ICP-AES analysis of 3 and 4 gave close Cu contents values of 0.14 and 0.12 mmol/g, respectively, indicating partial but equivalent Cu complexation for both catalysts (Table S3); it is remarkable to notice that the Cu center in 3 and 4 is the copper used for the CuAAC-grafting itself, hence reducing the preparation of the supported hybrid multifunctional catalysts to one single step from azide silica. 12 Nitrogen physisorption measurements showed a decrease in average pore size and surface area following CuAAC-grafting, which further confirm the efficient functionalization (Table S4).…”

Supported Tris-Triazole Ligands for Batch and Continuous-Flow Copper-Catalyzed Huisgen 1,3-Dipolar Cycloaddition Reactions

“…A second CuAAC step, in this case, with 4-azidomethylstyrene, led to the TBTA monomer 3 in a high overall yield and without the need for chromatographic purification in any stage of the synthetic sequence. Variants of P2 were reported in the following years to include soluble macromolecular analogs [20][21][22] and surface-immobilized TBTA units in microfluidic devices [23]. However, to the best of our knowledge, no supported TBTA material suitable for continuous-flow chemistry at a scale of truly preparative interest has been described to date (for recent examples of CuAAC in flow with other supported catalytic systems, see [13][14][15][16][24][25][26][27][28][29][30][31][32]).…”

“…Even though the preparation of 3 has been reported in the literature [20,21], at the beginning of this work, we set out to find a more convenient and scalable route for its synthesis. In particular, the goal was to avoid the use of expensive reagents and multiple chromatographic purification steps required by the published preparations of the TBTA monomer 3, or its direct precursor 4 [17,[20][21][22][23].…”

Silica–Polystyrene Hybrid Core/Shell Microparticles of Rhodium–Chiral Diene Complexes as Catalysts for Asymmetric 1,4-Addition Reactions

“…To address this issue, we have designed a core/shell type support in which low-cross-linking degree PS is attached on a rigid core material to maintain high mass transport efficiency and make the whole support insoluble, stable, and easy to handle (Figure b). There have been several reports of the immobilization of catalytic sites on core/shell-type supports, in which the catalytic centers were integrated on the outer surface to maintain high accessibility; − however, these systems tended to lack generality, the structures of the catalysts were not controlled well, and the relationship between structure and activity was not clear. , To immobilize sophisticated catalysts while maintaining their (enantio)­selectivities, we hypothesized that, in addition to the integration of catalytically active species on the outer surface, an inert shell backbone with low cross-linking degree on a rigid core might be an ideal strategy to create supports that would allow efficient mass transport to be retained. Herein, we have successfully immobilized a chiral catalyst while maintaining catalytic activity and enantioselectivity at levels comparable to those of the corresponding homogeneous catalyst in rhodium–diene complex catalyzed asymmetric 1,4-addition reactions.…”