Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2023 Mar 28;15(7):1671.
doi: 10.3390/polym15071671.

Supramolecular Linear-Dendritic Nanoreactors: Synthesis and Catalytic Activity in "Green" Suzuki-Miyaura Reactions

Xin Liu  1   2 , F Max Yavitt  1   3 , Ivan Gitsov  1   4
Affiliations

Supramolecular Linear-Dendritic Nanoreactors: Synthesis and Catalytic Activity in "Green" Suzuki-Miyaura Reactions

Xin Liu et al. Polymers (Basel). .

Abstract

This study describes the synthesis of novel amphiphilic linear-dendritic block copolymers and their self-assembly in water to form supramolecular nanoreactors capable of catalyzing Suzuki-Miyaura coupling reactions under "green" conditions. The block copolymers were formed through copper(I)-catalyzed alkyne-azide cycloaddition between azide functionalized poly(benzyl ether) dendrons as the perfectly branched blocks, as well as bis-alkyne modified poly(ethylene glycol), PEG, as the linear block. A first-generation poly(benzyl ether) dendron (G1) was coupled to a bis-alkyne modified PEG with molecular mass of 5 kDa, forming an ABA copolymer (G1)2-PEG5k-(G1)2 (yield 62%), while a second-generation dendron (G2) was coupled to a 11 kDa bis-alkyne modified PEG to produce (G2)2-PEG11k-(G2)2 (yield 49%). The structural purity and low dispersity of the linear-dendritic copolymers were verified by size-exclusion chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Their self-assembly was studied by dynamic light scattering, showing that (G1)2-PEG5k-(G1)2 and (G2)2-PEG11k-(G2)2 formed single populations of micelles (17 nm and 37 nm in diameter, respectively). The triazole rings located at the boundaries between the core and the corona are efficient chelating groups for transition metals. The ability of the micelles to complex Pd was confirmed by 1H NMR, transmission electron microscopy, and inductively coupled plasma. The catalytic activity of the supramolecular linear-dendritic/Pd complexes was tested in water by model Suzuki-Miyaura reactions in which quantitative yields were achieved within 3 h at 40 °C, while, at 17 °C, a yield of more than 70% was attained after 17 h.

Keywords: Suzuki coupling; block copolymer; linear-dendritic; self-assembly; “green” chemistry.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Scheme 1
Scheme 1
Synthesis of (G2)2−PEG−(G2)2. PEG5k: n = 97; PEG 11k: n = 233.
Figure 1
Figure 1
1H NMR spectra of PEG5k (A), bis-alkyne PEG5k (B), (G1)2−PEG5k−(G1)2 (C) and (G1)2−PEG5k−(G1)2/Pd complex (D). Blue labels: PEG protons, orange labels: bis-PPA protons, purple labels: methine/triazole protons, red labels: poly(benzyl ether) dendron protons. ×—solvent protons. See Section 2.2.3. in ‘Materials and Methods’ for analysis conditions.
Figure 2
Figure 2
Analysis of starting material PEG 5k, A, intermediate (alkyne)-PEG5k-(alkyne), B, and final products (G1)2−PEG5k−(G1)2, C, (G2)2−PEG5k−(G2)2, D: (a) Overlay of SEC eluograms; (b) Overlay of MALDI-TOF spectra. See Section 2.2.1 and Section 2.2.2 in Materials and Methods for analysis conditions.
Figure 3
Figure 3
Analysis of starting material PEG11k, A, intermediate (alkyne)−PEG11k−(alkyne), B, and final product (G2)2−PEG11k−(G2)2, C: (a) Overlay of SEC eluograms; (b) Overlay of MALDI-TOF spectra. See Section 2.2.1 and Section 2.2.2 in Materials and Methods for analysis conditions.
Figure 4
Figure 4
Structures of linear dendritic block copolymers containing the same amount of poly(benzyl ether) dendrons attached to the same PEG block (n = 233): (a) (G2)2−PEG11k−(G2)2, this work; (b) [G-3]−PEG11k−[G-3], [1,6].
Figure 5
Figure 5
Dynamic light scattering of aqueous solutions before (A) and after addition of PdCl2(PhCN)2 (B): (a) (G1)2−PEG5k−(G1)2 micelles; (b) (G2)2−PEG11k−(G2)2 micelles. See Section 2.2.5, Section 2.3.7 and Section 2.3.8 in ‘Materials and Methods’ for analysis conditions.
Figure 6
Figure 6
Aqueous solutions of PdCl2(PhCN)2: (a) without (G1)2−PEG5k−(G1)2 micelles; (b) with (G1)2−PEG5k−(G1)2 micelles.
Figure 7
Figure 7
Schematic cross-section representation of Pd loaded micelles formed in water by solvent displacement: (a) Monomolecular (G1)2−PEG5k−(G1)2 micellar Pd complex; (b) Multimolecular (G1)2−PEG5k−(G1)2 micellar Pd complex.
Figure 8
Figure 8
TEM micrographs of Pd-loaded linear dendritic block copolymers.: (a) (G1)2−PEG5k−(G1)2 micellar Pd complex; (b) (G2)2−PEG11k−(G2)2 micellar Pd complex. Scale bar: 50 nm. Red arrows mark possible Pd monomolecular micelle complexes. See Section 2.2.6 and Section 2.3.8 in ‘Materials and Methods’ for analysis conditions.
Scheme 2
Scheme 2
Synthesis of 4-acetylbiphenyl. 4′-BAcP:PBA:TEA (1:2:3 eq), water, 40 °C, 3 h.
See this image and copyright information in PMC

References

    1. Gitsov I., Fréchet J.M.J. Solution and solid-state properties of hybrid linear-dendritic block copolymers. Macromolecules. 1993;26:6536–6546. doi: 10.1021/ma00076a035. - DOI
    1. van Hest J.C.M., Baars M.W.P.L., Elissen-Roman C., van Genderen M.H.P., Meijer E.W. Acid-Functionalized Amphiphiles, Derived from Polystyrene-Poly(propylene imine) Dendrimers, with a pH-Dependent Aggregation. Macromolecules. 1995;28:6689–6691. doi: 10.1021/ma00123a043. - DOI
    1. Blasco E., Piñol M., Oriol L. Responsive Linear-Dendritic Block Copolymers. Macromol. Rapid Commun. 2014;35:1090–1115. doi: 10.1002/marc.201400007. - DOI - PubMed
    1. Gitsov I. Synthesis and Self-Assembly of Linear-Dendritic Hybrid Polymers. In: Kobayashi S., Müllen K., editors. Encyclopedia of Polymeric Nanomaterials. Springer; Berlin/Heidelberg, Germany: 2015. pp. 2436–2446. - DOI
    1. Liu X., Gitsov I. Nonionic Amphiphilic Linear-Dendritic Block Copolymers. Solvent-Induced Self-Assembly and Morphology Tuning. Macromolecules. 2019;52:5563–5573. doi: 10.1021/acs.macromol.9b01023. - DOI

LinkOut - more resources