Harald Maid

A meso-Helical Coordination Polymer from Achiral Dinuclear [Cu2(H3CCN)2(μ-pydz)3][PF6]2 and 1,3-Bis(diphenylphosphanyl)propane—Synthesis and Crystal Structure of {[Cu(μ-pydz)2][PF6]} (pydz=pyridazine)

Reaction of achiral [Cu2(H3CCN)2(mu-pydz)3][PF6]2 (1) (pydz = pyridazine) with bidendate 1,3-bis(diphenylphosphanyl)propane (2) in acetonitrile at room temperature in a 1:1 ratio yielded the mononuclear copper(I) complex [Cu[CH2(CH2PPh2)2]2][PF6] (3) together with new one-dimensional coordination polymer 1 to infinity[[Cu(mu-pydz)2][PF6]] (4). Air-sensitive single crystals of 4, suitable for X-ray structure determination, were grown from a mixture of dichloromethane/ hexane [crystal system: monoclinic; space group: C2/c: a = 21.910(3), b = 12.130(2), c = 25.704(3) A,beta = 110.08(10) degrees, V = 6416.65(16) A3]. The one-dimensional coordination polymer 1 to infinity[[Cu(mu-pydz)2][PF6]] (4) exhibits as outstanding feature the rare structure of a meso-helix.

Enantiomerisation of tetrahedral homochiral [M4L6] clusters: Synchronised four Bailar twists and six atropenantiomerisation processes monitored by temperature-dependent dynamic 1H NMR spectroscopy

Temperature-dependent 1H NMR studies prove homochiral, racemic [([symbol: see text])/([symbol: see text])]-((NH4)4[symbol: see text] [Mg4(L1)6]) (1) to be kinetically stable on the NMR timescale. Due to steric reasons, rotation around the central C-C single bond in (L1)2- is blocked, which prevents 1 from enantiomerisation. Most interestingly, however, the 1H NMR spectrum of racemic 2a reveals dynamic temperature dependence. This phenomenon can be explained by simultaneous Bailar twists at the four octahedrally coordinated magnesium centres, synchronised with the sterically unhindered atropenantiomerisation processes around the C-C single bonds of the six ligands (L2)2-, leading to the unprecedented enantiomerisation ([symbol: see text])-2a [symbol: see text] ([symbol: see text])-2a. The profound nondissociative rearrangement occurs without the formation of diastereoisomers. Supplementary support for the interpretation of the temperature-dependent dynamic 1H NMR spectra of 2a is presented by additional studies of [([symbol: see text])/([symbol: see text])]-((EtNH3)4 [symbol: see text] [Mg4(L2)6]) (2b). In 2a and 2b, the ether methylene protons exhibit identical temperature dependence. However, with addition, the methylene protons of the ethyl ammonium groups of 2b display similar temperature dependence as the ligand ether methylene protons.

Template and pH‐Mediated Synthesis of Tetrahedral Indium Complexes [Cs⊂{In4(L)4}]+ and [In4(HNL)4]4+: Breaking the Symmetry of N‐Centered C3 (L)3− To Give Neutral [In4(L)4]

There are two classes of well known T-symmetric complexes, in which four octahedrally coordinated metal ions are located in the apices of a tetrahedron, and each of the six edges are bridged by linear C2-symmetric bis(bidentate) chelators (L) and (L) . In [Cs {FeFe3(L)6}] (1), [M {Fe4(L )6}] + (2 ; M = NH4 , K, Cs), and [R4N {M4(L )6}] 11 (3 ; M = Fe, Ga), a cation is endohedrally encapsulated in the center of the tetrahedron, whereas in the complexes [M4\{M4(L)6}] (4) (M = NH4, RNH3: empty, K, Cs: H2O as guest; M 3 = Mg, Co, Ni, Mn), four cations are exohedrally centered above the four tetrahedral triangular faces (Figure 1). However, there are far fewer examples known of Tsymmetric complexes, in which the octahedrally coordinated metal centers in the vertices of the tetrahedra are linked by C3-symmetric tris(bidentate) chelators (L ) or (L) , which occupy the faces of the tetrahedra. Examples thereof

Iron Catalysis for In Situ Regeneration of Oxidized Cofactors by Activation and Reduction of Molecular Oxygen: A Synthetic Metalloporphyrin as a Biomimetic NAD(P)H Oxidase

A major challenge in biomimetic catalysis is the development of synthetic low-molecular-weight compounds that are able to mimic the catalytic function of enzymes. Thus, biomimetic redox enzymes should, on the one hand, be able to function as a catalyst in water and on the other hand accept cofactors, in particular NADH and NADPH (NAD(P) = nicotinamide adenine dinucleotide (phosphate)) and their oxidized forms NAD and NADP, respectively, as co-substrates. The in situ recycling of the expensive cofactors, a process carried out mostly by means of biotransformations, is considered a key technique for conducting enzymatic redox reactions in an attractive fashion. For the reduction mode of the cofactor regeneration (to regenerate the reduced forms NADH and NADPH) Steckhan et al. developed a “biomimetic formate dehydrogenase” for the regeneration of NAD(P)H by oxidation of formic acid into carbon dioxide by using a suitable rhodium complex. For the oxidation mode of the cofactor regeneration, NAD(P)H oxidases as natural catalysts have been applied as well as chemoenzymatic, electrochemical, and biomimetic catalyst systems. However, the biomimetic catalysts developed so far produce undesired hydrogen peroxide as a by-product instead of (preferably) water. To the best of our knowledge no biomimetic catalyst for the regeneration of NAD(P) from NAD(P)H by activation and reduction of molecular oxygen into water, similar to the mode of action of a NAD(P)H oxidase, is known. The mode of action of such a water-producing NAD(P)H oxidase is depicted in Scheme 1. In addition only a few synthetically suitable NAD(P)H oxidases, which serve as key tools for the “oxidative cofactor regeneration”, are known. However, in part these enzymes show a lack of stability under process conditions, different preferences for the two cofactors NADH and NADPH, and the production of unwanted hydrogen peroxide (instead of water) as a byproduct. Additionally, from this perspective the availability of an “artificial” biomimetic, water-producing NAD(P)H oxidase would be desirable and a valuable alternative to NAD(P)H-oxidase-type enzymes in preparative syntheses. Herein we report the application of a synthetic, watersoluble iron(III) porphyrin as an artificial, biomimetic waterproducing NAD(P)H oxidase. In analogy to enzymes, the metalloporphyrin is suitable for the in situ regeneration of both cofactors NAD and NADP by activation and reduction of molecular oxygen, and is also compatible with different preparative enzymatic oxidative reactions. Furthermore, to the best of our knowledge, this represents the first application of a synthetic metalloporphyrin as a catalyst for the activation and reduction of molecular oxygen into water by means of a natural cofactor in aqueous solution. Additionally a novel alternative is presented for carrying out enzymatic oxidation reactions under in situ regeneration of the oxidized cofactor NAD(P) by means of a non-enzymatic, synthetic catalyst serving as an “artificial enzyme mimic”. At the beginning of our work we searched for a lowmolecular-weight and water-soluble metal complex that accepts the natural cofactors NAD(P)H as a hydride donor for the activation of molecular oxygen, and would thereby be able to reduce oxygen into water while simultaneously being recycled as a catalyst. As the Fe porphyrin subunit, located in the active site of monooxygenases, exhibits comparable characteristics in the initial steps of monohydroxylation (though here a one-electron transfer involving a further cofactor takes place), we focused our preliminary screening on low-molecular-weight Fe complexes having a waterScheme 1. Concept of the NAD(P)H-oxidase-catalyzed or biomimetic in situ cofactor regeneration of NAD(P).

Enantiospecific Syntheses of Copper Cubanes, Double-Stranded Copper/ Palladium Helicates, and a (Dilithium)-Dinickel Coronate from Enantiomerically Pure Bis-1,3-diketones-Solid-State Self-Organization Towards Wirelike Copper/Palladium Strands

Enantiomerically pure, vicinal diols 1 afforded in a two-step synthesis (etherification and subsequent Claisen condensation) chiral bis-1,3-diketones H(2)L((S,S)) (3 a-c) with different substitution patterns. Reaction of these C(2)-symmetric ligands with various transition-metal acetates in the presence of alkali ions generated distinct polynuclear aggregates 4-8 by diastereoselective self-assembly. Starting from copper(II) acetate monohydrate and depending on the ratio of transition-metal ion to alkali ion to ligand, chiral tetranuclear copper(II) cubanes (C,C,C,C)-[Cu(4)(L((S,S)))(2)(OMe)(4)] (4 a-c) or dinuclear copper(II) helicates (P)-[Cu(2)(L((S,S)))(2)] (5) could be synthesized with square-pyramidal and square-planar coordination geometry at the metal center. In analogy to the last case, with palladium(II) acetate double-stranded helical systems (P)-[Pd(2)(L((S,S)))(2)] (6,7) were accessible exhibiting a linear self-organization of ligand-isolated palladium filaments in the solid state with short inter- and intramolecular metal distances. Finally, the introduction of hexacoordinate nickel(II) in combination with lithium hydroxide monohydrate and chiral ligand H(2)L((S,S)) (3 a) allowed the isolation of enantiomerically pure dinuclear nickel(II) coronate [(LiMeOH)(2) subset{(Delta,Lambda)-Ni(2)(L((S,S)))(2)(OMe)(2)}] (8) with two lithium ions in the voids, defined by the oxygen donors in the ligand backbone. The high diastereoselectivity, induced by the chiral ligands, during the self-assembly process in the systems 4-8 could be exemplarily proven by circular dichroism spectroscopy for the synthesized enantiomers of the chiral copper(II) cubane 4 a and palladium(II) helicate 6.

1D- and 2D-Coordination Polymers from Self-Complementary Building Blocks: Co-Crystallization of (P)- and (M)-Single-Stranded Diastereoisomers

Reaction of methanolic copper(II) acetate solution with oxazolidine 21 (HL7) led to the formation of the one-dimensional coordination polymer 1D-∞1[CuL27] 23. On the contrary, reaction of copper(II) acetate in methanol with pyrrolidine 24 (HL8) yielded the two-dimensional coordination polymer 2D-∞2[CuL28] 26. A common feature of 23 and 26 are the C2h-symmetric coordinatively unsaturated building blocks 22 and 25. In 1D-∞1[CuL27] 23, the cyano groups are linked to copper in a side-on fashion and the monomers 22 are oriented parallel to one another, whereas in 2D-∞2[CuL28] 26 the cyano groups are bound to copper in the end-on mode and the monomers 25 are oriented at an angle of 117° to one another. In both 1D-23 and 2D-26, copper has a distorted octahedral coordination sphere. On the other hand, reaction of methanolic copper(II) acetate solution with enantiomerically pure (5S)-pyrrolidine 27 (HL9(S)) led to the formation of the diastereomeric helical strands (M)-/(P)-1D-∞1[CuL29] 29. (M)- and (P)-29 are present in pairs in the infinite unit cell. In helical 1D-29, copper is tetragonal-pyramidally coordinated and the C2-symmetric monomers 28 (CuL29) are linked through only one cyano group. Moreover, it has been shown that the reaction of chiral racemic pyrrolidine 30 (HL10(R,S)) with copper(II) acetate via the intermediate Ci-symmetric building blocks 31 (CuL10(R)L10(S)) furnishes one-dimensional 1D-∞1[CuL10(R)L10(S)] 32. Single-crystal X-ray diffraction analyses of the supramolecular species 23, 26, 29, and 32 unequivocally establish the structures of these coordination polymers.

Metal–Organic Coordination Networks of Ferric Wheels, their Surface-supported Supramolecular Architectures and STM/STS Imaging

Six-membered ferric wheels [Fe6Cl6(L2)6] were generated from the corresponding N-alkylsubstituted diethanolamines (H2L2) {L2 = [®-N(CH2CH2O)2]2−; ® = Me-[CH2-]17 (3d); Me-[CH2-]19 (3e)}, calcium hydride and iron(III) chloride. Compound 3d was characterized by X-ray crystal structure analysis. The lipophilic tails of 3d interdigitate to create strands that, by lateral van der Waals interactions, pack to form 2D layers. The stacking of these sheets creates the final 3D architecture of the crystal. An elementary structure formation process of complex molecule 3d on highly oriented pyrolytic graphite (HOPG) was studied. Using scanning tunneling microscopy (STM) under ambient conditions, we succeeded in combining high-resolution topography mapping with simultaneous current–voltage characteristics (scanning tunneling spectroscopy, STS) measurements on single molecules deposited on HOPG surfaces. One of the most interesting results is that the location of the individual metal ions in their organic matrix is directly addressable by STS.

Fused Perylene–Phthalocyanine Macrocycles: A New Family of NIR‐Dyes with Pronounced Basicity

The synthesis and characterization of a new type of chromophore, namely PePc consisting of a central phthalocyanine core and four fused perylene-bisimide (PBI) units is described for the first time. The entire architecture represents a highly extended conjugated heterocyclic π-system with C4h symmetry. In order to guarantee pronounced solubility in organic solvents the corresponding PBI units were bay-functionalized with tert-butylphenoxy substituents. Next to the metal-free macrocycle, PePcH2 , also metallated macrocycles PePcM (M=Zn, Ni, Pb, Ru, Fe) were synthesized. The extensive fusion of the corresponding aromatic building blocks to the very large extended π-system leads to a very narrow HOMO-LUMO gap and as a consequence to transparency in the visible but light absorption in the NIR region. Significantly, the azomethine N-atoms N1N4 of PePcM and PePcH2 are highly basic. The corresponding tetraprotonated systems can only be deprotonated with very strong non-nucleophilic bases such as phosphazene bases. In the protonated forms PePcMH4 (4+) and PePcMH6 (4+) the absorption maximum is shifted back to the visible region due to the loss of conjugation. The experimental findings were corroborated with quantum mechanical calculations.

Organic Electron Acceptors Comprising a Dicyanomethylene-Bridged Acridophosphine Scaffold: The Impact of the Heteroatom

Stable two-electron acceptors comprising a dicyanomethylene-bridged acridophosphine scaffold were synthesized and their reversible reduction potentials were efficiently tuned through derivatization of the phosphorus center. X-ray crystallographic analysis combined with NMR, UV/Vis, IR spectroscopic, and electrochemical studies, supported by theoretical calculations, revealed the crucial role of the phosphorus atom for the unique redox, structural, and photophysical properties of these compounds. The results identify the potential of these electron deficient scaffolds for the development of functional n-type materials and redox active chromophores upon further functionalization.

Preparation of candidate reference materials for the determination of phosphorus containing flame retardants in styrene-based polymers

Candidate reference materials (RM) for the analysis of phosphorus-based flame retardants in styrene-based polymers were prepared using a self-made mini-extruder. Due to legal requirements of the current restriction for the use of certain hazardous substances in electrical and electronic equipment, focus now is placed on phosphorus-based flame retardants instead of the brominated kind. Newly developed analytical methods for the first-mentioned substances also require RMs similar to industrial samples for validation and verification purposes. Hence, the prepared candidate RMs contained resorcinol-bis-(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), triphenyl phosphate and triphenyl phosphine oxide as phosphorus-based flame retardants. Blends of polycarbonate and acrylonitrile-co-butadiene-co-styrene as well as blends of high-impact polystyrene and polyphenylene oxide were chosen as carrier polymers. Homogeneity and thermal stability of the candidate RMs were investigated. Results showed that the candidate RMs were comparable to the available industrial materials. Measurements by ICP/OES, FTIR and NMR confirmed the expected concentrations of the flame retardants and proved that analyte loss and degradation, respectively, was below the uncertainty of measurement during the extrusion process. Thus, the candidate RMs were found to be suitable for laboratory use.