Christian Eschbaumer

4′-Functionalized 2,2′:6′,2″-terpyridines as building blocks for supramolecular chemistry and nanoscience

Abstract Different mono- and bis-terpyridines were synthesized utilizing nucleophilic substitution of 4′-chloro-2,2′:6′,2″-terpyridine. In the case of the mono-functionalized ligands, different functional groups opposite to the metal binding site could be introduced; with the bis-functionalized ligands building blocks for metal-containing polymers with a tailored alkyl-chain length were accessible. As examples, a functionalized terpyridine cadmium(II) complex as well as a fullerene derivative were prepared.

Makromoleküle mit Bipyridin- und Terpyridinkomplexen als Verknüpfungsstellen: erste Schritte auf dem Weg zu metallo-supramolekularen Polymeren

Die Fahigkeit von Stickstoffheterocyclen, Ubergangsmetallionen wie Cobalt(II), Kupfer(II), Nickel(II) und Ruthenium(ii) auserordentlich effektiv und stabil zu komplexieren, wird schon seit langem in der Analytischen Chemie angewendet. In der Supramolekularen Chemie nutzte man spater diese Eigenschaft zum Aufbau anspruchsvoller Strukturen wie Helicate, Leitern oder Gitter. Die Entdeckung der Makromolekule durch Staudinger eroffnete bereits 1922 den Zugang zu einer Materialklasse mit bis dahin vollig unbekannten Eigenschaften. Erst in den letzten Jahrzehnten jedoch wurde versucht, die Makromolekulare und Supramolekulare Chemie durch die Entwicklung von metallkomplexierenden und metallhaltigen Polymeren mit Anwendungen von der Filtration bis zur Katalyse zu vereinen. Die entscheidende Anforderung an Materialien fur solche Anwendungen ist die Stabilitat der Polymer-Metallkomplexe. Besonders vielversprechend ist die Verwendung der mehrzahnigen Bipyridin- und Terpyridin-Chelatliganden, die sehr stabile Ubergangsmetallkomplexe mit beeindruckenden physikalischen Eigenschaften bilden. Ein breites Spektrum an Strukturen ist fur eine ebenso umfangreiche Zahl von Anwendungen entwickelt worden. Die Synthese von Polymeren auf Basis koordinativer Wechselwirkungen wurde dagegen bis vor wenigen Jahren nur in sehr wenigen Fallen realisiert und fuhrte daruber hinaus haufig zu geringen Ausbeuten. In den vergangenen Jahren jedoch erlebte die Forschung zu selbstorganisierten und supramolekularen Polymeren als neue, „intelligente“ Materialien mit einstellbaren Eigenschaften einen Hohenflug. In diesem Aufsatz geben wir einen Uberblick uber dieses Gebiet an der Schnittstelle von Supramolekularer und Makromolekularer Chemie.

Functionalized polymers with metal complexing segments : a simple and high-yield entry towards 2,2':6',2''-terpyridine-based oligomers

Williamson type ether reactions were utilized for a high yield reaction of 4′-chloro-2,2′:6′,2″-terpyridine with α,ω-dihydroxy-functionalized poly(ethylene oxide) and poly(oxytetramethylene)s to obtain bis(terpyridine)-terminated telechelics. The completeness of the functionalization was proven by NMR spectroscopy, GPC and MALDI-TOF-MS investigations. The addition of transition metal ions resulted in a polyaddition polymerization leading to the formation of extended metallo-supramolecular polymers, as proven by UV/VIS spectroscopy titration experiments.

Access to Heterogeneous Atom-Transfer Radical Polymerization (ATRP) Catalysts Based on Dipyridylamine and Terpyridine via Ring-Opening Metathesis Polymerization (ROMP)

Full Paper: A series of dipyridylamine and terpyridine derivatives, norborn-2-ene-5-di(pyrid-2-yl)carbamide (1), 49-(norborn-2-ene-5-ylmethyleneoxy)terpyridine (2), di-(pyrid-2-yl)acetamide (3) and bis(49-(norborn-2-ene-5ylmethyleneoxy)-2,29:69,299-terpyridine)iron(II) hexafluorophosphate (4) have been synthesized. Linear homopolymers, poly-1 and poly-2, as well as grafted and coated silica- and PS-DVB-based polymer supports have been prepared therefrom via ring-opening metathesis polymerization (ROMP). Monomer 3, poly-1, poly-2 have been loaded with Cu (I), Cu (II), Fe (II) as well as Hg (II) salts, respectively. These metal complexes as well as metal loaded supports based on compounds 1, 2 and 4 have subsequently been used for homogeneous and heterogeneous atom-transfer radical polymerization (ATRP) of styrene. Systems based on poly-2 coated silica loaded with Cu (I) were found to work best. Under optimum conditions, polystyrene was obtained in 30% yield with polydispersity indices a 1.6 within 2 h and with a remaining metal content in the ng/g (ppb)-range.

Directed Synthesis of Monofunctionalized 5,5'-Disubstituted 2,2'-Bipyridines and their first Application as Metallo-Supramolecular Initiators #

Abstract Monofunctionalized 5,5′-disubstitued 2,2′-bipyridines were synthesized in very high yields and used in a first application for the construction of a metal centered star-like AB block copolymer.

Characterization of Metallo-Supramolecular Systems by MALDI-TOF Mass Spectrometry

MALDI-TOF mass spectrometry was used for the characterization of metallo-supramolecular coordination arrays with molecular weights between 500 and 4000 g/mol. The stepwise loss of the counterions was used as an additional fingerprint for the investigated species. The isotope pattern yielded further information, especially in combination with simulations.

Self-assembled thin films of organo-metal complexes

Abstract Organo-metal complexes have been self-assembled into thin monomolecular films by adsorption onto polyelectrolyte covered substrates. The basic molecular building blocks of these systems consist of octahedral coordinating metal ions (Cu(II), Co(II), Zn(II), and Hg(II)) and terpyridines or fused terpyridines, held together by non-covalent interactions. The structure of the films has been characterized by synchroton based X-ray reflectivity and fluorescence techniques, clearly proving the successfull deposition of a close-packed monomolecular layer of complexes. First results of diffuse X-ray scattering indicate that the complexes exhibit no long-range lateral order, while however, forming a laterally homogeneous film.

Solution properties of supramolecular cobalt coordination arrays

A number of chemically related gridlike Co coordination arrays were studied by UV/vis absorption spectroscopy, electron microscopy and, in particular, analytical ultracentrifugation and partial specific volume measurements, in order to determine their solubility, stability and association behavior in a variety of organic solvents. As judged by the naked eye, solubilization of the compounds occurred instantaneously or at least within minutes. In contrast, the UV/ vis absorbance of the samples distinctly changed for hours or even days, depending on the compound in question. In some cases, the spectral changes indicated dissociation events, probably involving dissolution of clusters or microcrystals. This was supported by 1H NMR (on related Cd and Zn compounds) and electron microscopic observations at different time intervals after addition of the solvent. Under certain conditions, addition of 20–50 mM salt (necessary to obtain ultracentrifuge data not influenced by nonideal sedimentation behavior) again led to aggregation of the material. However, according to equilibrium sedimentation experiments in most solvents the solubilized Co coordination arrays finally were in the form of monomers, whereas in some solvents intermediate aggregates were predominant. Prolonged storage of the solubilized compounds at room temperature in most cases led to their decomposition or conversion. Reliably determining the partial specific volume, ν, of the compounds turned out to be the most difficult problem in our studies. Density measurements using a Paar density meter apparently suffered from disturbances (probably due to aggregation) at the relatively high compound concentrations required. v determinations applying the Edelstein—Schachman method to data collected in solvents of different density suffered from dependencies of v on the solvent. Combining measurements in nondeuterated and deuterated solvents (as in the original Edelstein—Schachman method) suffered from relatively low accuracy; in addition, it is applicable to a few solvents only. At present, weighted averages of the ν values from the different ultracentrifuge methods seem to yield the most reliable figures.

Terpyridine Based Metallo-Supramolecular Initiators: Towards Novel Self-Organizing Materials

Abstract[Fe(II){5,5″- bis(bromomethyl)-terpyridin}2](PF26)22 complexes were used as metallo-supramolecular initiators for the living polymerization of 2-ethyl-2-oxazolines yielding defined hydrophilic polymers with a central supramolecular building unit and star-like architectures. The living character of the polymerization allows an exact control of the molecular weight as well as the incorporation of additional (complexing) units at the polymer chain ends.

Exchange interaction and Jahn—Teller correlations in novel tetranuclear supramolecular Cu(II) grid complexes: an ESR study

Novel tetranuclear Cu(II) complexes in which four Cu(II) ions are arranged in a square planar fashion by four bis(bipyridyl)pyrimidine ligands were investigated by X and Q band ESR in the temperature range 4.2-300 K. The ESR spectra of this grid-like structure were well simulated as rising from triplet species. Analysis of their intensities allowed the spectra to be assigned to the first excited triplet state, and revealed intramolecular antiferromagnetic coupling of the Cu(II) spins. The isotropic exchange interaction J was determined as −47 K and reducing to about −5 K on functionalizing the bridging pyrimidine ring at the 2-position by methyl or phenyl. For comparison an ESR investigation was also carried out on the mononuclear analogue Cu(II)—(terpyridine)2 complexes with substituted terpyridine ligands at the 5′ and 5″ position. Depending on the substitutent, the spectra exhibit a static or dynamic Jahn—Teller effect at room temperature. The temperature dependence of their g-values is examined by a modified Silver—Getz model which includes cooperative Jahn—Teller interactions. There is evidence that both an anisotropic spin exchange contribution to D = 0.0159 cm−1 and a coupled (static) Jahn—Teller effect are responsible for efficient coupling between the four Cu(II) ions in the grid complexes with non-substituted pyrimidine bridges.