Guido Kickelbick

Concepts for the incorporation of inorganic building blocks into organic polymers on a nanoscale

Hybrid inorganic – organic materials are promising systems for a variety of applications due to their extraordinary properties based on the combination of the different building blocks. The combination of nanoscale inorganic moieties with organic polymers has a high potential for future applications and has therefore attracted a lot of attention during the last years. Since there are countless different combinations of the two moieties, there are also a large number of methodologies to combine them in one material. This review is written with the intention to give an overview of principal concepts of the preparation of such materials for different applications. It focuses on the chemical aspects of the incorporation of inorganic building blocks such as silica networks, porous materials, metals, etc. into an organic polymeric matrix. q 2002 Elsevier Science Ltd. All rights reserved.

Synthesis of Co2Pt, Co2Pd and MoPd2 mixed-metal clusters with the P–N–P assembling ligands (Ph2P)2NH (dppa) and (Ph2P)2NMe (dppaMe). Crystal structure of [Co2Pt(μ3-CO)(CO)6(μ-dppa)]

Heterometallic triangular platinum–cobalt, palladium–cobalt and palladium–molybdenum clusters stabilized by one or two bridging diphosphine ligands such as Ph2PNHPPh2 (dppa) or (Ph2P)2NMe (dppaMe) or by mixed ligand sets Ph2PCH2PPh2 (dppm)/dppa have been prepared with the objectives of comparing the stability and properties of the clusters as a function of the short-bite diphosphine ligand used and of the metal carbonyl fragment they contain. Ligand redistribution reactions were observed during the purification of [Co2Pd(μ3-CO)(CO)4(μ-dppa)(μ-dppm)] (4) by column chromatography with the formation of [Co2Pd(μ3-CO)(CO)4(μ-dppm)2] and the dinuclear complex [(OC)2Cl] (5). The latter was independently prepared by reaction of [Pd(dppa-P,P′)2](BF4)2 with Na[Co(CO)4]. Attempts to directly incorporate the ligand (Ph2P)2N(CH2)3Si(OMe)3 (dppaSi) into a cluster or to generate it by N-functionalization of coordinated dppa were unsuccessful, in contrast to results obtained recently with related clusters. The crystal structure of [Co2Pt(μ3-CO)(CO)6(μ-dppa)] (1) has been determined by X-ray diffraction.

AN UNUSUAL RING STRUCTURE OF AN OLIGOMERIC OXOTITANIUM ALKOXIDE CARBOXYLATE

Ti9O8(OPr)4(methacrylate)16 was obtained by the reaction of Ti(OPr)4 with an excess of methacrylic acid and analyzed by X-ray diffraction. The compound consists of a ring of nine [TiO6] octahedra linked by six μ2- and only two μ3-oxide bridges.

4,4', 4-Tris(5-nonyl)-2,2' : 6', 2-terpyridine as ligand in atom transfer radical polymerization (ATRP)

The bulk atom transfer radical polymerization (ATRP) of styrene or methyl acrylate was carried out in the presence of CuCl or CuBr complexed by equimolar amounts of 2,2′: 6′,2″-terpyridines (tpy) as ligands. Uncontrolled reactions were observed in the presence of unsubstituted ligands whereas relatively fast but controlled polymerization of styrene and methyl acrylate was observed for CuCl and CuBr complexed by tpy with three 5-nonyl substituents (tNtpy). Molecular weights evolved linearly with conversion and polymers with relatively low polydispersities were formed (Mw/Mn < 1.2).

SYNTHESIS, STRUCTURE AND ELECTROCHEMICAL STUDIES OF THE FIRST MIXED-METAL CLUSTERS WITH THE P-N-P ASSEMBLING LIGANDS (PH2P)2NH (DPPA), (PH2P)2N(CH3) ( DPPAM) AND (PH2P)2N(CH2)3SI(OET)3 (DPPASI)

Heterometallic triangular palladium–cobalt clusters stabilized by three bridging diphosphine ligands such as Ph 2 PNHPPh 2 (dppa), (Ph 2 P) 2 N(CH 3 ) (dppam), (Ph 2 P) 2 N(CH 2 ) 3 Si(OEt) 3 (dppaSi), or mixed ligand sets Ph 2 PCH 2 PPh 2 (dppm)/dppa, dppm/dppam or dppm/dppaSi have been prepared with the objectives of comparing the stability and properties of the clusters as a function of the short-bite diphosphine ligand used and of making possible their use in the sol–gel process (case of dppaSi). The crystal structure determination of [CoPd 2 ( μ 3 -CO) 2 ( μ -dppam) 3 ]PF 6 confirms the triangular arrangement of the metal core, with each edge bridged by a dppam ligand, although disorder problems prevent a detailed discussion of the bonding parameters. Different approaches are given to functionalize the heterometallic clusters: alkylation of the nitrogen atom of co-ordinated dppa ligands or introduction of a third bridging diphosphine in a precursor tetranuclear cluster containing only two bridging diphosphine ligands. In the latter case, it was found that their nature critically determined whether or not the reaction occurred. The diversity of bridging ligands allowed an investigation of their influence on the electrochemical properties of the clusters. By comparison with [CoPd 2 ( μ 3 -CO) 2 (CO) 2 ( μ -dppm) 2 ] + which contains only two assembling ligands, it is generally observed that trinuclear cationic CoPd 2 clusters containing three (identical or different) edge-bridging bidentate diphosphine ligands show increased redox flexibility. A notable stabilisation of the metal core is observed when three dppm ligands bridge the metal–metal bonds and [CoPd 2 ( μ 3 -CO) 2 ( μ -dppm) 3 ] reversibly undergoes either a single-step two-electron oxidation or two distinct one-electron reductions. Complexes with the other diphosphines exhibit similar redox behaviour, but the stability of their redox congeners depends upon the nature of the diphosphine: a lower redox aptitude is exhibited by the dppa and dppam derivatives [CoPd 2 ( μ 3 -CO) 2 ( μ -dppa) 3 ] + and [CoPd 2 ( μ 3 -CO) 2 ( μ -dppam) 3 ] + .

Structural comparison of CuII complexes in atom transfer radical polymerization

The molecular structures of [CuII(dNbpy)2Br]+[CuIBr2]−, CuII(pmdeta)Br2, CuII(tNtpy)Br2, [CuII(hmteta)Br]+[Br]− and [CuII(cyclam)Br]+[Br]− [dNbpy=4,4′-di(5-nonyl)-2,2′-bipyridine, pmdeta=N,N,N′,N″,N″-pentamethyldiethylenetriamine, tNtpy=4,4′,4″-tris(5-nonyl)-2,2′:6′,2″-terpyridine, hmteta=1,1,4,7,10,10-hexamethyltriethylenetetramine, Me4cyclam=1,4,8,11-tetraaza-1,4,8,11-tetramethylcyclotetradecane] isolated from atom transfer radical polymerizations (ATRP) were determined. The CuII complexes showed either a trigonal bipyramidal structure as in the case of the dNbpy ligand, or a distorted square pyramidal coordination in the case of triamines and tetramines. Depending on the type of amine ligand, the complexes were either neutral (triamines) or ionic (bpy and tetramines). The counterions in the case of the ionic complexes were either bromide (Me4cyclam and hmteta) or the linear [CuIBr2]− anion (dNbpy). No direct correlation was found between the CuII–Br bond length and the deactivation rate constant in ATRP, which suggests that other parameters such as the entropy for the structural reorganization between the CuI and CuII complexes might play an important role in determining the overall activity of the catalyst in ATRP.

Methacrylate‐Substituted Mixed‐Metal Clusters Derived from Zigzag Chains of [ZrO8]/[ZrO7] and [TiO6] Polyhedra

Reaction of titanium butoxide and zirconium butoxide with methacrylic acid in different molar ratios results in the formation of the mixed-metal clusters Ti4Zr4O6(OBu)4(OMc)16, Ti2Zr4O4(OBu)2(OMc)14, Ti4Zr2O4(OBu)6(OMc)10, and Ti2Zr6O6(OMc)20 (OMc = methacrylate). The molecular structures of these clusters have been determined by single-crystal X-ray diffraction analysis. They are based on a common structural motif, namely a zigzag chain comprising two terminal [TiO6] octahedra and two or four central [ZrO8] dodecahedra or [ZrO7] pentagonal bipyramids sharing common edges. Two additional [TiO6] octahedra or [ZrO8] dodecahedra are condensed at the flank of the main chain.

Synthesis and crystal structures of multifunctional tosylates as basis for star-shaped poly(2-ethyl-2-oxazoline)s

Summary The synthesis of well-defined polymer architectures is of major importance for the development of complex functional materials. In this contribution, we discuss the synthesis of a range of multifunctional star-shaped tosylates as potential initiators for the living cationic ring-opening polymerization (CROP) of 2-oxazolines resulting in star-shaped polymers. The synthesis of the tosylates was performed by esterification of the corresponding alcohols with tosyl chloride. Recrystallization of these tosylate compounds afforded single crystals, and the X-ray crystal structures of di-, tetra- and hexa-tosylates are reported. The use of tetra- and hexa-tosylates, based on (di)pentaerythritol as initiators for the CROP of 2-ethyl-2-oxazoline, resulted in very slow initiation and ill-defined polymers, which is most likely caused by steric hindrance in these initiators. As a consequence, a porphyrin-cored tetra-tosylate initiator was prepared, which yielded a well-defined star-shaped poly(2-ethyl-2-oxazoline) by CROP as demonstrated by SEC with RI, UV and diode-array detectors, as well as by 1H NMR spectroscopy.

Transition metal oxide-doped mesostructured silica films

Abstract Mixed metal oxide-doped mesostructured silica films have been prepared by a combination of a ligand-assisted templating (LAT) and solvent evaporation-induced self-assembly (EISA) approach using metal alkoxides as precursors. To overcome the problem of the different hydrolysis and condensation rates of the various alkoxide precursors (silicon alkoxides and transition metal alkoxides), the hydrophilic head group of oligo(ethylene oxide) containing surfactants was coordinated to the M(OR) x groups resulting in metal-containing surfactants. These novel surfactants serve different functions in the EISA process: first, they moderate the hydrolysis and condensation rate of the transition metal alkoxide; second, they allow for a positioning of the transition metal alkoxide within the silica matrix; and third, they act as structure-directing agents. The obtained films are characterized by a high loading of the transition metal oxide species within the silica matrix and a homogeneous distribution throughout the whole film as shown by X-ray photoelectron (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Several transition metal oxides have been incorporated into the silica matrix such as titania, zirconia and tantalum oxide.

Cluster-Crosslinked Inorganic-Organic Hybrid Polymers: Influence of the Cluster Type on the Materials Properties

Methacrylate-substituted tetranuclear tantalum, zirconium and titanium oxide clusters (Zr4O2(OMc)12, Ti4O2(OPri)6(OMc)6, and Ta4O4(OEt)8(OMc)4) were prepared by reaction of the alkoxides with methacrylic acid. The clusters were then polymerized with methyl methacrylate as co-monomers in different molar ratios (0.5–2 mol% of the functionalized cluster). In the resulting inorganic-organic hybrid polymers, the clusters crosslink the polymer chains very efficiently. The physical properties and structural features of the hybrid polymers, investigated by their swelling behavior, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), 13C MAS NMR and impedance spectroscopy, exhibit a clear dependence on the cluster portion in the polymer and on the cluster type.