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Groningen, Netherlands

Harder S.,Stratingh Institute for Chemistry
Zeitschrift fur Anorganische und Allgemeine Chemie

The Manzer benzyl ligand, ortho-Me2N-benzyl (DMA), has been introduced in lanthanide (Ln) chemistry more than three decades ago with the syntheses of Sc(DMA)3 and Er(DMA)3 but no reaction chemistry or structures have been described. Only recently it was shown that a Ln(DMA)3 complex can also be obtained for the largest Ln metal lanthanum and first crystal structures appeared. At present crystal structures of many Ln(DMA)3 complexes throughout the series have been determined and were found to be isomorphous. This reports describes the improvement of synthetic methods for Ln(DMA)3 complexes, a discussion on structures and trends and more important, the wide scope of Ln(DMA)3 reagents as versatile building-blocks in lan-thanide chemistry: the fast-growing number of complexes and catalysts that have been made starting from a Ln(DMA)3 reagent are summarized. Despite the intramolecular chelating Me2N arm, half-sandwich catalysts containing the DMA fragment are still active in alkene polymerizations or other catalytic conversions. The main advantages of Ln(DMA)3 complexes are: i) easy syntheses from commercially available starting materials, ii) convenient crystallization which warrants high purity, iii) high stability on account of intramolecular coordination while sufficient reactivity for further conversions is maintained and iv) availability of these reagents over the full Ln range which is advantageous for catalyst screening. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Intemann J.,Stratingh Institute for Chemistry | Sirsch P.,University of Tubingen | Harder S.,Friedrich - Alexander - University, Erlangen - Nuremberg
Chemistry - A European Journal

In analogy to the previously reported tetranuclear magnesium hydride cluster with a bridged dianionic bis-β-diketiminate ligand, a related zinc hydride cluster has been prepared. The crystal structures of these magnesium and zinc hydride complexes are similar: the metal atoms are situated at the corners of a tetrahedron in which the vertices are bridged either by dianionic bis-β-diketiminate ligands or hydride ions. Both structures are retained in solution and show examples of H-⋯H- NMR coupling (Mg: 8.5 Hz; Zn: 16.0 Hz). The zinc hydride cluster [NN-(ZnH)2] 2 thermally decomposes at 90 C and releases 1.8 equivalents of H 2. In contrast to magnesium hydride clusters, there is no apparent relationship between cluster size and thermal decomposition temperature for the zinc hydrides. DFT calculations reproduced the structure of the zinc hydride cluster reasonably well and charge density analysis showed no bond paths between the hydride ions. This contrasts with calculations on the analogous magnesium hydride cluster in which a counter-intuitive H-⋯H- bond path was observed. Forcing a reduced H-⋯H- distance in the zinc hydride cluster, however, gave rise to a H -⋯H- bond path. Such weak interactions could play a role in H2 desorption. The presumed molecular product after H 2 release, a Zn(I) cluster, could not be characterized experimentally but DFT calculations predicted a cluster with two localized Zn-Zn bonds. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Intemann J.,Stratingh Institute for Chemistry | Intemann J.,Friedrich - Alexander - University, Erlangen - Nuremberg | Lutz M.,Bijvoet Center for Biomolecular Research | Harder S.,Friedrich - Alexander - University, Erlangen - Nuremberg

Multinuclear magnesium hydride complexes react with pyridine, forming 1,2- and 1,4-dihydropyridide (DHP) complexes. Reaction of PARA3Mg8H10 with pyridine initially formed 1,2-DHP and 1,4-DHP product mixtures which converted at 60 °C into PARA-[Mg(1,4-DHP)]2·(pyridine)2 (PARA = [(2,6-iPr2C6H3)NC(Me)C(H)C(Me)N]2-(p-C6H4)). Reaction of [NN-(MgH)2]2 with pyridine gave exclusive formation of the 1,2-DHP product NN-[Mg(1,2-DHP)]2·(pyridine)2 (NN = [(2,6-iPr2C6H3)NC(Me)CHC(Me)N-]2). Both products were characterized by crystal structure determinations. The unusual preference for 1,2-addition is likely caused by secondary intramolecular interactions based on mutual communication between the metal coordination geometries: an extended network of C-H···C π-interactions and π-stacking interactions is found. Whereas PARA3Mg8H10 is hardly active in magnesium-catalyzed hydroboration of pyridines with pinacolborane, [NN-(MgH)2]2 shows efficient coupling. However, the regioselectivity of the stoichiometric reaction is not translated to the catalytic regime. This result is taken as an indication for a potential alternative mechanism in which magnesium hydride intermediates do not play a role but the hydride is transferred from an intermediate borate complex. © 2014 American Chemical Society. Source

Spielmann J.,Universitatsstrasse 5 | Harder S.,Stratingh Institute for Chemistry
Dalton Transactions

The bis-β-diketimine with a meta-phenylene bridge (META-H2: DIPPN(H)CMeCHCMeN-C6H4-NCMeCHCMeN(H)DIPP; DIPP = 2,6-iPr-C6H3) reacted with two equivalents of nBu 2Mg to give the bis-β-diketiminate complex META-(MgnBu) 2. The latter binuclear magnesium complex was converted to META-[MgNH(iPr)BH3]2 by reaction with H 2N(iPr)BH3. The thermal decomposition of this binuclear iPr-substituted magnesium amidoborane complex has been investigated. In benzene it starts to eliminate H2 at 90 °C. Two decomposition products could be obtained by fractional crystallization of the residue. The first product is the trinuclear magnesium complex META-Mg3[iPrNB(H)N(iPr) BH3]2 and the second product is (META-Mg)2. These products have been formed by ligand exchange reactions of the expected complex META-Mg2[iPrNB(H)N(iPr)BH3] and were characterized by single crystal X-ray diffraction. The central Mg2+ ion in META-Mg3[iPrNB(H)N(iPr)BH3]2 is not connected to the ligand system and its coordination geometry could be representative of that in a solid-state magnesium salt containing the RNB(H)N(R)BH 3 2- ion. © The Royal Society of Chemistry 2011. Source

Szymanski W.,Stratingh Institute for Chemistry | Yilmaz D.,University of Groningen | Kocer A.,University of Groningen | Feringa B.L.,Stratingh Institute for Chemistry
Accounts of Chemical Research

If we look at a simple organism such as a zebrafish under a microscope, we would see many cells working in harmony. If we zoomed in, we would observe each unit performing its own tasks in a special aqueous environment isolated from the other units by a lipid bilayer approximately 5 nm thick. These confined units are social: they communicate with one another by sensing and responding to the chemical changes in their environment through receptors and ion channels. These channels control the highly specific and selective passage of ions from one side of the cell to the other and are embedded in lipid bilayers. The movement of ions through ion channels supports excitation and electrical signaling in the nervous system.Ion channels have fascinated scientists not only because of their specificity and selectivity, but also for their functions, the serious consequences when they malfunction, and the other potential applications of these molecules. Light is a useful trigger to control and manipulate ion channels externally. With the many state-of-the-art optical technologies available, light offers a high degree of spatial and temporal control, millisecond precision, and noninvasive intervention and does not change the chemical environment of the system of interest.In this Account, we discuss research toward the dynamic control of lipid bilayer assembly and channel function, particularly the transport across the lipid bilayer-ion channel barrier of cells using light. We first summarize the manipulation of ion channel activity with light to modulate the channel's natural activity. Based on the type of photoswitch employed, we can achieve novel functionalities with these channels, and control neural activity. Then we discuss the recent developments in light-induced transport through lipid bilayers. We focus on three different approaches: the incorporation of photoswitchable copolymers into the lipids, the doping of the lipid bilayer with photosensitive amphiphiles and the preparation of the lipid bilayers solely from photoswitchable lipids.These examples reflect the versatility of what we can achieve by manipulating biological systems with light, from triggering the permeability of a specific area of a lipid bilayer to controlling the behavior of a whole organism. © 2013 American Chemical Society. Source

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