Klaus Eichele Publication Abstracts 2017

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[UP]	J.-J. Maudrich, C. P. Sindlinger, F. S. W. Aicher, K. Eichele, H. Schubert, L. Wesemann: Reductive Elimination of Hydrogen from Bis(trimethylsilyl)methyltin Trihydride and Mesityltin Trihydride Chem. Eur. J. 2017, 23(9), 2192-2200. DOI: 10.1002/chem.201605317

Alkyltin trihydride [(Me3Si)(2)CHSnH3] was synthesized and the reductive elimination of hydrogen from this species was investigated. A methyl-substituted N-heterocyclic carbene reacts with the organotrihydride in dependence on stoichiometry and solvent to give a series of products of the reductive elimination and dehydrogenative tin-tin bond formation. Besides characterization of the carbene adduct of the alkyltin(II) hydride, a Sn-4 chain was also isolated, encompassing two stannyl-stannylene sites, which are stabilized each as NHC-adducts. Complete dehydrogenation resulted to give either a carbene-stabilized distannyne or a metalloid Sn-9-cluster salt. Reductive elimination of hydrogen was also achieved with an excess of diethylmethylamine to give the alkyltin(II) hydride as a Lewis base free tetramer [(RSnH)(4)]. The method of cluster formation at low temperatures by hydrogen elimination was also transferred to the mesityl-substituted tin trihydride MesSnH(3). In this case [(MesSn)(10)], showing a [5] prismane structure, was isolated in good yield and characterized. NMR spectroscopic features of the propellane-type cluster [Trip(6)Sn(6)] are reported.

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[UP]	D. Schmid, A. Seyboldt, K. Eichele, D. Kunz: Synthesis of a lithium-cyclopentadienide complex by addition of LiNTf2 to a zwitterionic fulvalene Dalton Trans. 2017, 46(1), 29-32. DOI: 10.1039/c6dt03355e

The synthesis of a eta(5)-coordinated LiCp complex by simple addition of a Li-salt in benzene is presented. A strongly zwitterionic fulvalene serves as the Cp-precursor. Evidence for the coordination of Li+ was obtained by the characterisitic Li-7 NMR chemical shifts, variable temperature experiments in solution and by X-ray structure analysis in the solid state.

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[UP]	R. Schmidt, M. Strobele, K. Eichele, H.-J. Meyer: Crystal Structure and Luminescence Investigations of the Nitridomagnesoaluminates Mg3AlnNn+2 with n=1, 2, 3 Eur. J. Inorg. Chem. 2017(20), 2727-2735. DOI: 10.1002/ejic.201700255

Mg3Al3N5, Mg3Al2N4, and Mg3AlN3 were synthesized at 1100 degrees C in a closed system by utilizing weld-shut niobium ampoules. Their crystal structures were solved and refined on the basis of powder XRD data in space group P6(3)/mmc [a = b = 3.2422(1), c = 26.340(1) angstrom, Z = 2] for Mg3Al3N5, P (3) over bar m1 [a = b = 3.2860(1), c = 10.7461(1) angstrom, Z = 1] for Mg3Al2N4, and R (3) over barm [a = b = 3.3683(0), c = 25.4835(1) angstrom, Z = 3] for Mg3AlN3. Their crystal structures are characterized by wurtzite-type [AlN] and [MgN] block layers alternating with octahedral [MgN] layers along the c-axis direction. Europium(III)-doped samples of Mg3Al3N5 show characteristic emission in the visible region of the spectrum on excitation with UV radiation at lambda(ex) = 370 nm. Mg3AlN3 doped with europium(II) shows yellow luminescence on excitation with UV radiation at lambda(ex) = 365 nm.

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[UP]	J. Schneider, C. P. Sindlinger, K. Eichele, H. Schubert, L. Wesemann: Low-Valent Lead Hydride and Its Extreme Low-Field H-1 NMR Chemical Shift J. Am. Chem. Soc. 2017, 139(19), 6542-6545. DOI: 10.1021/jacs.7b01856

Although hydrides of the group 14 elements are well-known as versatile starting materials in many chemical transformations, a hydride of lead hi oxidation state II is so far unknown. In this work, we finally complete the jigsaw puzzle by reporting the isolation of the first low valent organolead hydride. The thermolabile dimeric organolead hydride was synthesized at low temperature and features a hydride H-1 NMR signal (in solution 35.61 ppm in the solid state 31.1 ppm) at the lowest field observed so far for a diamagnetic compound in agreement with quantum chemical predictions.

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[UP]	P. Meixner, K. Batke, A. Fischer, D. Schmitz, G. Eickerling, M. Kalter, K. Ruhland, K. Eichele, J. E. Barquera-Lozada, N. P. M. Casati, F. Montisci, P. Macchi, W. Scherer: J(Si,H) Coupling Constants of Activated Si-H Bonds J. Phys. Chem. A 2017, 121(38), 7219-7235. DOI: 10.1021/acs.jpca.7b05830

We outline in this combined experimental and theoretical NMR study that sign and magnitude of J(Si,H) coupling constants provide reliable indicators to evaluate the extent of the oxidative addition of Si-H bonds in hydrosilane complexes. In combination with experimental electron density studies and MO analyses a simple structure-property relationship emerges: positive J(Si,H) coupling constants are observed in cases where M -> L pi-back-donation (M = transition metal; L = hydrosilane ligand) dominates. The corresponding complexes are located close to the terminus of the respective oxidative addition trajectory. In contrast negative J(Si,H) values signal the predominance of significant covalent Si-H interactions and the according complexes reside at an earlier stage of the oxidative addition reaction pathway. Hence, in nonclassical hydrosilane complexes such as Cp2Ti(PMe3)(HSiMe3-nCln) (with n = 1-3) the sign of J(Si,H) changes from minus to plus with increasing number of chloro substituents n and maps the rising degree of oxidative addition. Accordingly, the sign and magnitude of J(Si,H) coupling constants can be employed to identify and characterize nonclassical hydrosilane species also in solution. These NMR studies might therefore help to reveal the salient control parameters of the Si-H bond activation process in transition-metal hydrosilane complexes which represent key intermediates for numerous metal-catalyzed Si-H bond activation processes. Furthermore, experimental high-resolution and high-pressure X-ray diffraction studies were undertaken to explore the close relationship between the topology of the electron density displayed by the eta(2)(Si-H)M units and their respective J(Si,H) couplings.