21 research outputs found
ROMP Synthesis of CobalticeniumâEnamine 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 <sup>1</sup>H, <sup>13</sup>C NMR,
and DOSY NMR, IR, UVâvis 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 <sup>1</sup>H 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<sup>I</sup> Catalysis of âClickâ 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<sup>I</sup>-catalyzed alkyneâazide cycloaddition (CuAAC)
âclickâ reactions of various substrates in water using
the catalyst CuÂ(hexabenzyltren)Br (tren = triaminoethylamine). Moreover
this recyclable nanoreactor with intradendritic triazole rings strongly
also activates the simple SharplessâFokin catalyst CuSO<sub>4</sub> + sodium ascorbate in water under ambient conditions leading
to exceptional TONs up to 510â000. 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
âClickâ Synthesis of Nona-PEG-branched Triazole Dendrimers and Stabilization of Gold Nanoparticles That Efficiently Catalyze <i>p</i>âNitrophenol 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 HAuCl<sub>4</sub> in water to these
dendrimers quantitatively leads to the intradendritic formation of
AuCl<sub>3</sub>(trz) moieties subsequent to complete Cl<sup>â</sup> substitution by trz on AuÂ(III), whereas the analogous complexation
reaction of AuCl<sub>3</sub> with a linear PEG trz ligand forms only
an equilibrium between trz-coordinated AuÂ(III) and AuÂ(III) that is
not coordinated to trz. Reduction of the dendrimer-AuÂ(III) complexes
to Au<sup>0</sup> by NaBH<sub>4</sub> 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 AuÂ(III) addition per
dendritic trz followed by NaBH<sub>4</sub> 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, AuÂ(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 NaBH<sub>4</sub> 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
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, [FeCpÂ(η<sup>6</sup>-ethynylmesitylene)]Â[PF<sub>6</sub>], <b>3</b>, easily available from [FeCpÂ(η<sup>6</sup>-mesitylene)]Â[PF<sub>6</sub>], <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<sup>I</sup> species
Visible-Light Generation of the Naked 12-Electron Fragment C<sub>5</sub>H<sub>5</sub>Fe<sup>+</sup>: Alkyne-to-Vinylidene Isomerization and Synthesis of Polynuclear Iron Vinylidene and Alkynyl Complexes Including Hexairon Stars
Visible-light photolysis of [FeCpÂ(η<sup>6</sup>-C<sub>6</sub>H<sub>5</sub>CH<sub>3</sub>)]Â[PF<sub>6</sub>] using
a simple 100-W
bulb or a compact fluorescent light bulb in the presence of terminal
alkynes and dppe yielded the vinylidene complexes [FeCpÂ(î»Cî»CHR)Â(dppe)]Â[PF<sub>6</sub>] that were deprotonated by <i>t</i>-BuOK to yield
the alkynyl complexes [FeCpÂ(-CîŒCR)Â(dppe)]. The reaction has
been extended to the synthesis of bis-, tris, tetra-, and hexanuclear
iron complexes including three alkynes of the ferrocenyl family
âClickâ 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<sup>I</sup> 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<sup>III/II</sup> wave (18e/19e) and generation dependent reversibility of the Co<sup>II/I</sup> (19e/20e) wave in DMF. The H<sub>2</sub>PO<sub>4</sub><sup>â</sup> anion is only recognized by the largest metallodendrimer <b>6</b> by a significant cathodic shift of the Co<sup>III/II</sup> 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>-Bu<sub>4</sub>N]Â[BAr<sub>4</sub><sup>F</sup>] {Ar<sup>F</sup> = 3,5-bisÂ(trifluoroÂmethyl)Âphenyl}
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 bisÂ(biferroÂcenyl)Âdiyne. Oxidation of all
of these polyÂ(biferroÂcenyl) complexes using a ferricinium
salt yields blue, robust biferrocenium complexes. Their localized
mixed-valent electronic structure was demonstrated at both MoÌssbauer
and infrared time scales even with the counteranion (BAr<sub>4</sub><sup>F</sup>) 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
âClickâ 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 âClickâ Cu<sup>I</sup> Catalyst in Water
The copperÂ(I)-catalyzed azide alkyne
cycloaddition (CuAAC) using
the conventional SharplessâFokin catalyst that consists of
CuSO<sub>4</sub> + Na ascorbate, the most well-known and used âclickâ
reaction, is considerably accelerated by the addition of a trisÂ(triazolyl)-polyÂ(ethylene
glycol) (tris-trz-PEG) amphiphilic ligand in water under ambient conditions.
Only parts per million amount of Cu<sup>I</sup> were necessary to
reach quantitative yields with TONs up to 86000 and TOFs of 3600 h<sup>â1</sup>. 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