New Amphiphilic Imidazolium/Benzimidazolium Calix[4]arene Derivatives: Synthesis, Aggregation Behavior and Decoration of DPPC Vesicles for Suzuki Coupling in Aqueous Media.

Vladimir Burilov,Ramilya Garipova,Svetlana Solovieva,Elsa Sultanova,Ilya Grigoryev,Diana Mironova,Igor Antipin

doi:10.3390/nano10061143

Vladimir Burilov, Ramilya Garipova + Show 5 more

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https://doi.org/10.3390/nano10061143

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Journal: Nanomaterials	Publication Date: Jun 10, 2020
Citations: 14	License type: CC BY 4.0

Affiliation: Kazan Federal University

Abstract

In this study, new types of amphiphilic calix[4]arene derivatives bearing N-alkyl/aryl imidazolium/benzimidazolium fragments were designed and synthesized by two step transformation: Regioselective Blanc chloromethylation of distal-di-O-butyl calix[4]arene and subsequent interaction with N-Substituted imidazole/benzimidazole. Critical aggregation concentration (CAC) values were estimated using pyrene fluorescent probe. Obtained macrocycles were found to form submicron particles with electrokinetic potential +44–+57 mV in aqueous solution. For the first time it was found that amphiphilic calixarene causes the fast transformation of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) multilamellar vesicles into unilamellar ones and leads to the ordering of the lipid in membranes at the molar calixarene/DPPC ratio more than 0.07. In situ complexes of calixarene aggregates with Pd(OAc)2 were found to be active in Suzuki–Miyaura coupling of 1-bromo-4-nitrobenzene with phenylboronic acid in water. It was shown that bulky N-substituents of heterocycle decrease the catalytic activity of the aggregates. These result can be assigned to the inhibition effect of Pd(II) complex in situ formation by bulky substituents located on the aggregate surface. Embedding of the most active palladium N-heterocyclic carbene (NHC) complex with methylimidazolium headgroups into DPPC vesicles enhances its catalytic activity in Suzuki–Miyaura coupling.

Highlights

Effective approaches to the new carbon–carbon and carbon–heteroatom bond formation are attracting a lot of attention among chemists [1,2]
Synthesis of Imidazolium/Benzimidazolium Calix[4]arene Derivatives. As it was previously shown by Schatz group, tetra-O-alkyl calixarene derivatives bearing at the distal positions of upper rim two [(3-N-substituted imidazolium-1-yl)methyl] fragments formed stable N-heterocyclic carbenes and corresponding cis/trans Pd(II) complexes which effectively catalyzed Suzuki–Miyaura coupling [25,26]
This structural motive of N-heterocyclic carbene (NHC) precursors with two imidazolium fragments on the upper rim seems to be very attractive for designing self-organizing systems for different catalytic transformations in water

Summary

Introduction

Effective approaches to the new carbon–carbon and carbon–heteroatom bond formation are attracting a lot of attention among chemists [1,2]. One of the most important tools is cross-coupling reactions, available to synthetic chemists in their quest to create artificial (or reproduce natural) organic scaffolds [3]. A special place in the cross-coupling catalysis has been occupied by palladium complexes with N-heterocyclic carbene (NHC) ligands [4,5,6]. The most attractive property of NHC complexes is their stability to moisture and air oxygen, allowing to perform specific catalytic reactions in aqueous media without inert atmosphere [7,8]. NHC complexes with amphiphilic properties allow to combine both micellar and metallocomplex types of catalysis in aqueous media [10,11]. The design of new amphiphilic NHC complexes is very promising for enhancing the cross-coupling reactions’ efficiency

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