Metallo-polymers

The ability of the boron atom of 59 to engage in a donor-acceptor interaction was illustrated with DMAP and DABCO (DABCO = diazabi-cyclo-[2.2.2]-octane) that readily formed the corresponding Lewis adducts. Interestingly, a similar behavior was retained after coordination of the phosphorus atom to palladium. The formation of the Lewis base adducts 66a and 66b of complex 65 (Scheme 38) was supported by solid-state 31P and nB CP/MAS-NMR spectroscopy (<5 1 B = 5-6 ppm), although the occurrence of decomposition and/or dissociation processes impeded spectroscopic characterization in solution and recrystallization to obtain X-ray quality crystals. Compounds 66a and 66b substantiate the ability of ambiphilic compounds to engage concomitantly into the coordination of donor and acceptor moieties. Such a dual behavior opens interesting perspectives for the preparation of metallo-polymers and multimetallic complexes. 

Polymers that consist of metal atoms joined together in a linear array are quite rare. This is because such systems prefer to collapse to three-dimensional clusters—literally very small chunks of metal stabilized on the surface by ligands. However, many of the intriguing electrical properties proposed for linear metallo polymers might be realized if a non-metallo polymer, such as a polyphosphazene, were used as a template and scaffold to stabilize a string of metal atoms and prevent cluster formation (structures 3.67 and 3.68). This has been accomplished only in a very preliminary and tentative way,... 

The resulting materials were difficult to work with because of a lack of solubility. By heating solutions containing low molecular weight PVP (Mjj 3900) and Ru(trpy)(bpy)H202+ in ethanol it was possible to prepare and isolate a series of well-defined metallo-polymers where the py/Ru ratio varied from 2/l to 20/l (27). 

Pomogailo AD, Rozenberg AS, DzhardimaUeva GI. (2005) In Nicolais L, Carotenuto, GH (eds) Controlled pyrolysis of metal-containing precursors as a way for synthesis of metallo-polymer nanocomposites, metab olymer nanocomposites. Wiley, New York, p. 75. 

A second wave is also predicted, but it was not observed experimentally due to the large overpotential required to oxidize Fe " at the support electrode. Typically a value of Ir given by 4.5 X 10 "F Acm was obtained. Electron-hopping current were obtained using potential step chronoamperometry (see Chapter 2). Typically is = 2.9 X IQ-io/F Acm The value of is was obtained via an indirect route. The corresponding Fe(III/II) reduction process was examined at the metallo-polymer. The reduction via mediation is thermodynamically unfavorable, so only the direct reduction at the inner interface should be observed. 

Schliitter F, Wild A, Winter A, Hager MD, Baumgaertel A, Friebe C, Schubert US (2010) Synthesis and characterization of new self-assembled metallo-polymers containing electron-withdrawing and electron-donating bis(terpyridine) zinc(n) moieties. Macromolecules 43 2759-2771... 

These ideas might be used to explain the interesting results obtained recently by Williams et al.53 These workers observed formation of crystalline polystyrene when the reaction was initiated by triphenyl methyl potassium (or some other potassium metallo-organic compounds) in a hexane solution, but an amorphous polymer was formed in benzene. They point out that the catalyst is soluble in benzene but insoluble in hexane, and suggest that the heterogeneity of the catalyst is responsible for the results. Although this might be the case, an alternative explanation could be advanced.42 1... 

Organometallic compounds are considered only with strong restrictions, namely when organic ligands, e.g., methyl groups, are introduced to avoid formation of coordination polymers, as is the case with mononuclear metallo-onium complexes. 

Researchers have already been using ink jet systems to print several types of novel materials, some of which have been used to fabricate circuit electrodes and interconnects. The four main types of materials used are metallo-organics, conductive polymers, molten metals, and metallic nanoparticle suspensions. 

An interesting novel approach to the synthesis of (metallo)dendrimer catalysts could be the use of random hyperbranched polymers [38]. Obviously, these hyperbranched polymers have comparable but less defined structures, but to arrive at dendrimers with similar sizes, a larger number of preparative steps are required, which may be an economic disadvantage. Furthermore, materials involving heterogeneous supports with well-defined metallodendritic subunits [15] can be a promising future direction giving rise to new types of supramolecu-lar catalysts that can easily be recovered from production streams. 

The halogen atoms remaining can then be replaced by organic residues such as trifluoroethoxy units. High polymers can also be prepared by ring-opening polymerization of the chlorocyclo-phosphazene, XXVIII. Compounds of this type can be converted to nldo-carboranes in the presence of base, but these do not form metallo-derivatlves, presumably for sterlc reasons (29). 

Schubert US, Eschbaumer C Angew Chem Int Ed (2002) 41 2892-2926 Macromolecules containing bipyridine and terpyridine metal complexes towards metallo-supramolecular polymers... 

Schmatloch S, van den Berg AMJ, Fijten MWM, Schubert US (2004) A high-throughput approach towards tailor-made water-soluble metallo-supramolecular polymers. Macromol Rapid Commun 25 321-325... 

Lohmeijer BGG, Schubert US (2003) Water-soluble building blocks for metallo-supramo-lecular polymers synthesis, complexation and decomplexation studies of poly(ethylene-oxide) moities. Macromol Chem Phys 204 1072-1078... 

Lohmeijer BGG, Schubert US (2004) Expanding the supramolecular polymer LEGO system nitroxide mediated living free radical polymerization for metallo-supramolecular block copolymers with a polystyrene block. J Polym Sci Part A Polym Chem 42 4016-4027... 

Beck JB, Rowan SJ. Multistimuli, multiresponsive metallo-supramolecular polymers. J Am Chem Soc 2003 125 13922-13923. 

Iyer PK, Beck JB, Weder C, Rowan SJ. Synthesis and optical properties of metallo-supramolecular polymers. Chem Commun 2005 (3) 319-321. 

Loveless DM, Jeon SL, Craig SL. Chemoresponsive viscosity switching of a metallo-supramo-lecular polymer network near the percolation threshold. J Mater Chem 2007 17 56-61. 

Over the last few years there has been an explosion of interest in this area and compounds displaying selective absorption, ion exchange and even catalytic properties have been reported.[1-3] Metallo-organic polymers do offer greater potential for chemical and structural diversity than traditional zeolite micro-porous solids, but are plagued by low dimensionality, lattice interpenetration and framework instability. Experience in constructing such materials can address most of these problems. 

On the basis of a catalytic system previously developed by the same group, Nicholls and collaborators [51] reported the preparation of an imprinted polymer for enantioselective formation of a C-C bond with properties of a metallo-enzyme aldolase type II. Polymers were imprinted using the two enantiomers of a 1,3-diketone, the (l.S, 35,45)-(75), and the corresponding (l/ ,3/ ,4/ )-(75), together with two 4-vinyl-pyridine held in place by a Co(II). The cross-aldol condensation... 

The spacer units in 3.60 are assembled from polyphosphazenes that bear p-bromophc-noxy side groups via a lithiation reaction, and treatment with a diorganochlorophosphine to give 3.62. The chemistry is summarized in reaction sequence (45).107 Polymer 3.62 coordinates to a variety of metallo species,108 including osmium cluster compounds and cobalt carbonyl hydroformylation catalysts. When used as a polymeric hydroformylation catalyst, this latter species proved how stable the polyphosphazene backbone is under the drastic conditions often needed for these types of reactions. The weakest bonds in the molecule proved to be those between the phosphine phosphorus atoms and the aromatic spacer groups. 

After publication of our work,22 new self-assembled Zn(II) terpyridine polymers were prepared and used in PLEDs. Following the methodology reported by us, Lin et al. similarly prepared a series metallopolymers by self-assembled reaction containing Zn(II) terpyridine units, including a metallo-homopolymer and metallo-u/t-copolymer containing carbazole pendants attached to the C-9 position of fluorene by long alkyl spacers.27... 

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