‘Click’ Synthesis and Redox Properties of Triazolyl Cobalticinium Dendrimers

The supramolecular redox functions of metallomacromolecules

Abstract

Metallomacromolecules are frequently encountered in redox proteins including metal-tanned hide collagen and play crucial roles involving supramolecular properties in biological electron-transfer processes. They are also currently found in non-natural families, such as: metallopolymers, metallodendrimers and metallodendronic polymers. This mini-review discusses the supramolecular redox functions of such nanomaterials developed in our research group. Electron-transfer processes are first examined in mono-, bis- and hexa-nuclear ferrocenes and other electron-reservoir organoiron systems showing the influence of supramolecular and reorganization aspects on their mechanism. Then applications of electron-transfer processes using these same organoiron redox systems in metallomacromolecules and their supramolecular functions are discussed including redox recognition/sensing, catalysis templates, electrocatalysis, redox catalysis, molecular machines, electrochromes, drug delivery device and nanobatteries.

Graphical Abstract

'Click' conjugated porous polymer nanofilm with a large domain size created by a liquid/liquid interfacial protocol

A liquid/liquid interfacial method is used to synthesize a conjugated porous polymer nanofilm with a large domain size. Copper-catalyzed azide-alkyne cycloaddition between a triangular terminal alkyne and azide monomers at a water/dichloromethane interface generates a 1,2,3-triazole-linked polymer nanofilm featuring a large aspect ratio and robustness against heat and pH.

Electrochemical Anion Sensing: Supramolecular Approaches

Anions play a vital role in a broad range of environmental, technological, and physiological processes, making their detection/quantification valuable. Electroanalytical sensors offer much to the selective, sensitive, cheap, portable, and real-time analysis of anion presence where suitable combinations of selective (noncovalent) recognition and transduction can be integrated. Spurred on by significant developments in anion supramolecular chemistry, electrochemical anion sensing has received considerable attention in the past two decades. In this review, we provide a detailed overview of all electroanalytical techniques that have been used for this purpose, including voltammetric, impedimetric, capacititive, and potentiometric methods. We will confine our discussion to sensors that are based on synthetic anion receptors with a specific focus on reversible, noncovalent interactions, in particular, hydrogen- and halogen-bonding. Apart from their sensory properties, we will also discuss how electrochemical techniques can be used to study anion recognition processes (e.g., binding constant determination) and will furthermore provide a detailed outlook over future efforts and promising new avenues in this field.

N-Heterocyclic Carbenes in Materials Chemistry

N-Heterocyclic carbenes (NHCs) have become one of the most widely studied class of ligands in molecular chemistry and have found applications in fields as varied as catalysis, the stabilization of reactive molecular fragments, and biochemistry. More recently, NHCs have found applications in materials chemistry and have allowed for the functionalization of surfaces, polymers, nanoparticles, and discrete, well-defined clusters. In this review, we provide an in-depth look at recent advances in the use of NHCs for the development of functional materials.

Recyclable magnetic nanoparticles grafted with antimicrobial metallopolymer-antibiotic bioconjugates

Over-prescription and improper use of antibiotics has led to the emergence of bacterial resistance, posing a major threat to public health. There has been significant interest in the development of alternative therapies and agents to combat antibiotic resistance. We report the preparation of recyclable magnetic iron oxide nanoparticles grafted with charged cobaltocenium-containing metallopolymers by surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization. β-Lactam antibiotics were then conjugated with metallopolymers to enhance their vitality against both Gram-positive and Gram-negative bacteria. The enhanced antibacterial activity was a result of synergy of antimicrobial segments that facilitate the inhibition of hydrolysis of antibiotics and local enhancement of antibiotic concentration on a nanoparticle surface. These magnetic nanoparticles can be recycled numerous times without losing the initial antimicrobial potency. Studies suggested negligible toxicity of metallopolymer-grafted nanoparticles to red blood cells and minimal tendency to induce resistance in bacteria.

Click Co sandwich-terminated dendrimers as polyhydride reservoirs and micellar templates

Neutral click metallodendrimers with [Co^I(η⁴-cyclopentadiene)(η⁵-cyclopentadienyl)] termini are synthesized by reduction of dendrimers with 9, 27 or 81 cobalticenium termini and serve as polyhydride reservoirs and reductants; for instance, they reduce proton sources to H₂ and Au^III to micellized capsules of gold nanoparticles.

Liquid/Liquid Interfacial Synthesis of a Click Nanosheet

A liquid/liquid interfacial synthesis is employed, for the first time, to synthesize a covalent two-dimensional polymer nanosheet. Copper-catalyzed azide-alkyne cycloaddition (CuAAC) between a three-way terminal alkyne and azide at a water/dichloromethane interface generates a 1,2,3-triazole-linked nanosheet. The resultant nanosheet, with a flat and smooth texture, has a maximum domain size of 20 μm and minimum thickness of 5.3 nm. The starting monomers in the organic phase and the copper catalyst in the aqueous phase can only meet at the liquid/liquid interface as a two-dimensional reaction space; this allows them to form the two-dimensional polymer. The robust triazole linkage generated by irreversible covalent-bond formation allows the nanosheet to resist hydrolysis under both acidic and alkaline conditions, and to endure pyrolysis up to more than 300 °C. The coordination ability of the triazolyl group enables the nanosheet to act as a reservoir for metal ions, with an affinity order of Pd²⁺ >Au³⁺ >Cu²⁺ .

Functional Materials Based on Metal-Containing Polymers

Since the dawn of human civilization, there has been a demand for materials that include ceramics, metals, and polymers. Increasing demand as well as the need for enhanced performance has driven material scientists to research metal-containing polymers as complements of these materials. Consequently, metal-containing polymers that integrate the excellent thermal, electronic, optical, and magnetic properties of metals with the lightweight, low cost, and in some cases, the chemical stability of organic-based polymers have been designed, and used as catalysts, sensors, ceramic precursors, magnetic materials, and electrical conductors. This chapter provides an overview of some of these functional metal-containing polymers.

Recent advances in click chemistry applied to dendrimer synthesis

Dendrimers are monodisperse polymers grown in a fractal manner from a central point. They are poised to become the cornerstone of nanoscale devices in several fields, ranging from biomedicine to light-harvesting. Technical difficulties in obtaining these molecules has slowed their transfer from academia to industry. In 2001, the arrival of the "click chemistry" concept gave the field a major boost. The flagship reaction, a modified Hüisgen cycloaddition, allowed researchers greater freedom in designing and building dendrimers. In the last five years, advances in click chemistry saw a wider use of other click reactions and a notable increase in the complexity of the reported structures. This review covers key developments in the click chemistry field applied to dendrimer synthesis from 2010 to 2015. Even though this is an expert review, basic notions and references have been included to help newcomers to the field.

Ring-opening metathesis polymerization of 18-e Cobalt(I)-containing norbornene and application as heterogeneous macromolecular catalyst in atom transfer radical polymerization

In the last decades, metallopolymers have received great attention due to their various applications in the fields of materials and chemistry. In this article, a neutral 18-electron exo-substituted η(4) -cyclopentadiene CpCo(I) unit-containing polymer is prepared in a controlled/"living" fashion by combining facile click chemistry and ring-opening meta-thesis polymerization (ROMP). This Co(I)-containing polymer is further used as a heterogeneous macromolecular catalyst for atom transfer radical polymerization (ATRP) of methyl methacrylate and styrene.

Sandwich complex-containing macromolecules: property tunability through versatile synthesis

Sandwich complexes feature unique properties as the physical and electronic properties of a hydrocarbon ligand or its derivative are integrated into the physical, electronic, magnetic, and optical properties of a metal. Incorporation of these complexes into macromolecules results in intriguing physical, electrical, and optical properties that were hitherto unknown in organic-based macromolecules. These properties are tunable through well-designed synthetic strategies. This review surveys many of the synthetic approaches that have resulted in tuning the properties of sandwich complex-containing macromolecules. While the past two decades have seen an ever-growing number of research publications in this field, gaps remain to be filled. Thus, we expect this review to stimulate research interest towards bridging these gaps, which include the insolubility of some of these macromolecules as well as expanding the scope of the sandwich complexes.

Facile preparation of cobaltocenium-containing polyelectrolyte via click chemistry and RAFT polymerization

A facile method to prepare cationic cobaltocenium-containing polyelectrolyte is reported. Cobaltocenium monomer with methacrylate is synthesized by copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction between 2-azidoethyl methacrylate and ethynylcobaltocenium hexafluorophosphate. Further controlled polymerization is achieved by reversible addition-fragmentation chain transfer polymerization (RAFT) by using cumyl dithiobenzoate (CDB) as a chain transfer agent. Kinetic study demonstrates the controlled/living process of polymerization. The obtained side-chain cobaltocenium-containing polymer is a metal-containing polyelectrolyte that shows characteristic redox behavior of cobaltocenium.