ROMP Synthesis of Cobalticenium–Enamine Polyelectrolytes

The synthesis of redox-robust polyelectrolyte polymers has long been investigated. Two simple methods of synthesis of well-defined cobalticenium-containing polymers are presented using both the norbornene ring-opening-metathesis polymerization (ROMP) method initiated by a third-generation Grubbs catalyst and the mild uncatalyzed hydroamination of the easily available ethynyl cobalticenium hexafluorophosphate salt. In the first strategy, a norbornene monomer functionalized with an enamine-cobalticenium group is polymerized by ROMP, whereas in the second one a norbornene derivative functionalized with a secondary amine group is polymerized by ROMP using the same catalyst followed by hydroamination of ethynyl cobalticenium. The structures of the polymers have been established by ¹H, ¹³C NMR, and DOSY NMR, IR, UV–vis spectroscopy, mass spectrometry, elemental analysis, and cyclic voltammetry. The number of units in the polymers have been determined for various polymer lengths using end-group analysis by ¹H NMR using the diffusion coefficient determined by DOSY NMR and by cyclic voltammetry upon comparing the relative intensities of a monomer reference and the cobalticenium polymers

Recyclable Catalytic Dendrimer Nanoreactor for Part-Per-Million Cu^I Catalysis of “Click” Chemistry in Water

Upon catalyst and substrate encapsulation, an amphiphilic dendrimer containing 27 triethylene glycol termini and 9 intradendritic triazole rings serves as a catalytic nanoreactor by considerably accelerating the Cu^I-catalyzed alkyne–azide cycloaddition (CuAAC) “click” reactions of various substrates in water using the catalyst Cu­(hexabenzyltren)Br (tren = triaminoethylamine). Moreover this recyclable nanoreactor with intradendritic triazole rings strongly also activates the simple Sharpless–Fokin catalyst CuSO₄ + sodium ascorbate in water under ambient conditions leading to exceptional TONs up to 510 000. This fully recyclable catalytic nanoreactor allows to considerably decrease the amount of this cheap copper catalyst down to industrially tolerable residues, and some biomedical and cosmetic applications are exemplified

“Click” Synthesis of Nona-PEG-branched Triazole Dendrimers and Stabilization of Gold Nanoparticles That Efficiently Catalyze <i>p</i>‑Nitrophenol Reduction

Two new water-soluble 1,2,3-triazole-containing nona-PEG-branched dendrimers are obtained with nine intradendritic 1,2,3-triazoles (trz). Addition of HAuCl₄ in water to these dendrimers quantitatively leads to the intradendritic formation of AuCl₃(trz) moieties subsequent to complete Cl^– substitution by trz on Au­(III), whereas the analogous complexation reaction of AuCl₃ with a linear PEG trz ligand forms only an equilibrium between trz-coordinated Au­(III) and Au­(III) that is not coordinated to trz. Reduction of the dendrimer-Au­(III) complexes to Au⁰ by NaBH₄ then leads to stabilization of gold nanoparticles (AuNPs) in water. The sizes of the AuNPs stabilized by the dendritic macromolecules are further controlled between 1.8 and 12 nm upon selecting the stoichiometry of Au­(III) addition per dendritic trz followed by NaBH₄ reduction. With a 1:1 Au/trz stoichiometry, the AuNP size depends on the length of the PEG tether of the dendrimer; small dendrimer-encapsulated AuNPs are formed with PEG2000, whereas large AuNPs are formed with PEG550. With Au/trz stoichiometries larger than unity, Au­(III) is reduced outside the macromolecule, resulting in the formation of large interdendritically stabilized AuNPs. The formation of very small and only mildly stabilized AuNPs by neutral hydrophilic triazole ligands offers an opportunity for very efficient <i>p</i>-nitrophenol reduction by NaBH₄ in water at the AuNP surface

Rhodicenium Salts: From Basic Chemistry to Polyelectrolyte and Dendritic Macromolecules

A new, facile synthesis of rhodicenium chloride is described, leading to the synthesis of rhodicenium tetraarylborate, the first rhodicenium salt that is soluble in less polar solvents. This opens the route to further chemistry that was prevented by the insolubility of the formerly available rhodicenium salts. This strategy has been extended to the synthesis of water-soluble polyelectrolyte and dendritic macromolecular cobaltocenium and rhodicenium salts

Visible-Light Generation of the Naked 12-Electron Fragment C₅H₅Fe⁺: Alkyne-to-Vinylidene Isomerization and Synthesis of Polynuclear Iron Vinylidene and Alkynyl Complexes Including Hexairon Stars

Visible-light photolysis of [FeCp­(η⁶-C₆H₅CH₃)]­[PF₆] using a simple 100-W bulb or a compact fluorescent light bulb in the presence of terminal alkynes and dppe yielded the vinylidene complexes [FeCp­(CCHR)­(dppe)]­[PF₆] that were deprotonated by <i>t</i>-BuOK to yield the alkynyl complexes [FeCp­(-CCR)­(dppe)]. The reaction has been extended to the synthesis of bis-, tris, tetra-, and hexanuclear iron complexes including three alkynes of the ferrocenyl family

Click Chemistry of an Ethynylarene Iron Complex: Syntheses, Properties, and Redox Chemistry of Cationic Bimetallic and Dendritic Iron-Sandwich Complexes

The functionalization of dendrimers and other macromolecules with cationic redox-active organometallics remains a target toward metal-containing dendrimers and polymers that can serve in particular as polyelectrolytes and multielectron redox reagents. Along this line, we report the click functionalization of organometallics and dendrimers with a redox-active ethynylarene iron complex, [FeCp­(η⁶-ethynylmesitylene)]­[PF₆], <b>3</b>, easily available from [FeCp­(η⁶-mesitylene)]­[PF₆], <b>1</b>. Complex <b>3</b> reacts with azidomethylferrocene upon catalysis by copper sulfate and sodium ascorbate (CuAAC reaction) to give a bimetallic complex that is reduced on the mesitylene ligand to a mixture of isomeric cyclohexadienyl complexes. Complex <b>3</b> also reacts according to the same click reaction with zeroth- and first-generation metallodendrimers containing, respectively, 9 and 27 azido termini to provide new polar polycationic metallodendrimers that are reversibly reduced, on the electrochemical time scale, to 19-electron Fe^I species

‘Click’ Synthesis and Redox Properties of Triazolyl Cobalticinium Dendrimers

The derivatization of macromolecules with redox-stable groups is a challenge for molecular electronics applications. The large majority of redox-derivatized macromolecules involve ferrocenes, and there are only a few reports with cobalticinium. We report here the first click derivatization of macromolecules with the cobalticinium redox group using ethynylcobalticinium hexafluorophosphate, <b>1</b>. Cu^I catalysis was used for these selective click metallodendrimer syntheses starting from <b>1</b> and providing the tripodal dendron <b>3</b> that contains three 1,2,3-triazolylcobalticinium termini and a phenol focal point and the dendrimers of generations 0, 1, and 2 containing 9, 27, and 81 triazolylcobalticinium units for the dendrimers <b>4</b>, <b>5</b>, and <b>6</b>, respectively. Atomic force microscopy (AFM) statistical studies provided the progression of height upon increase of dendrimer generation. Cyclic voltammetry studies in MeCN and dimethylformamide (DMF) show the solvent-dependent reversibility of the Co^III/II wave (18e/19e) and generation dependent reversibility of the Co^II/I (19e/20e) wave in DMF. The H₂PO₄^– anion is only recognized by the largest metallodendrimer <b>6</b> by a significant cathodic shift of the Co^III/II wave

Poly(Biferrocenylethynyl)arene and Bis(biferrocenyl)diynyl Complexes and Their Redox Chemistry

Orange linear bis-, star tris-, and dendritic tetra-biferrocenes linked by rigid ethynylaryl and diynyl spacers were synthesized through Sonogashira coupling and homocoupling reactions and oxidized to robust blue biferrocenium complexes. The proximity of the two ferrocenyl units to each other in the biferrocenyl units introduces electrostatic and electronic effects that are observed by cyclic voltammetry and are responsible for mixed-valence stabilization and localization. The use of the polyfluorinated electrolyte [<i>n</i>-Bu₄N]­[BAr₄^F] {Ar^F = 3,5-bis­(trifluoro­methyl)­phenyl} allows observing considerable enhancement of these effects and separation of electrochemical waves representing the two ferrocenyl groups of the biferrocenyl unit. The electrostatic effect is also selectively observed with the latter electrolyte between the two central ferrocenyl units of bis­(biferro­cenyl)­diyne. Oxidation of all of these poly­(biferro­cenyl) complexes using a ferricinium salt yields blue, robust biferrocenium complexes. Their localized mixed-valent electronic structure was demonstrated at both Mössbauer and infrared time scales even with the counteranion (BAr₄^F) that provokes the maximum electrostatic effect and very much enhances the difference between the two oxidation potentials. Their near-infrared spectra show the intervalent charge transfer and are similar to those previously recorded for biferrocenium and derivatives, confirming the class-II mixed valence. The biferrocene units around the arene linker are completely electronically independent in the neutral and cationic complexes. In conclusion, from a practical standpoint, the easy oxidation of these stiff electrochromic nanosystems and the largely increased robustness of their oxidized form compared to ferricinium make their potential use as electrochromes considerably more attractive than that of simple ferrocene derivatives

“Click” Assemblies and Redox Properties of Arene- and Gold-Nanoparticle-Cored Triazolylbiferrocene-Terminated Dendrimers

Large dendritic assemblies terminated by organometallic groups that possess a rich redox chemistry and stability in two or more oxidation states are highly desired as electron-reservoir systems, sensors, and redox catalysts. Here the synthesis and click (CuAAC) chemistry of ethynyl biferrocene including branching onto dendrons, arene-cored dendrimers, and gold nanoparticles are developed, and the role of the 1,2,3-triazole linkers and redox chemistry of these assemblies are discussed including the properties and stabilities of the redox states

Design and Applications of an Efficient Amphiphilic “Click” Cu^I Catalyst in Water

The copper­(I)-catalyzed azide alkyne cycloaddition (CuAAC) using the conventional Sharpless–Fokin catalyst that consists of CuSO₄ + Na ascorbate, the most well-known and used “click” reaction, is considerably accelerated by the addition of a tris­(triazolyl)-poly­(ethylene glycol) (tris-trz-PEG) amphiphilic ligand in water under ambient conditions. Only parts per million amount of Cu^I were necessary to reach quantitative yields with TONs up to 86000 and TOFs of 3600 h^–1. The ligand was fully recycled, and the catalyst was reused at least six times without decomposition. Large-scale syntheses were also successfully achieved with 93% yield. The catalyst was applied to the efficient synthesis of various useful functional products with medicinal, catalytic, targeting, and labeling properties