Klaus Eichele Publication Abstracts 2006

 

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[UP]	B. A. Demko, K. Eichele, R. E. Wasylishen: A Combined Experimental and Quantum Chemistry Study of Selenium Chemical Shift Tensors J. Phys. Chem. A 2006, 110, 13537-13550. DOI 10.1021/jp064543s

A comprehensive investigation of selenium chemical shift tensors is presented. Experimentally determined chemical shift tensors were obtained from solid-state ⁷⁷Se NMR spectra for several organic, organometallic, or inorganic selenium-containing compounds. The first reported indirect spin-spin coupling between selenium and chlorine is observed for Ph₂SeCl₂ where ¹J(⁷⁷Se,³⁵Cl)iso is 110 Hz. Selenium magnetic shielding tensors were calculated for all of the molecules investigated using zeroth-order regular approximation density functional theory, ZORA DFT. The computations provide the orientations of the chemical shift tensors, as well as a test of the theory for calculating the magnetic shielding interaction for heavier elements. The ZORA DFT calculations were performed with nonrelativistic, scalar relativistic, and scalar with spin-orbit relativistic levels of theory. Relativistic contributions to the magnetic shielding tensor were found to be significant for (NH₄)₂WSe₄ and of less importance for organoselenium, organophosphine selenide, and inorganic selenium compounds containing lighter elements.

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[UP]	T. Gädt, B. Grau, K. Eichele, I. Pantenburg, L. Wesemann: Ruthenium complexes with the stanna-closo-dodecaborate ligand: coexistence of h1(Sn) and h3(B-H) coordination Chem. Eur. J. 2006, 12, 1036-1045. DOI 10.1002/chem.200500761

Four stanna-closo-dodecaborate complexes of ruthenium have been prepared and characterized by multinuclear NMR studies in solution and in the solid state. The solid-state structures of the dimeric zwitterions [{Ru(dppb)(SnB11H11)}2] (2) (dppb=bis(diphenylphosphino)butane), [{Ru(PPh3)2(SnB11H11)}2] (3), and the dianionic ruthenium complex [Bu3MeN]2[Ru(dppb){2,7,8-(-H)3-exo-SnB11H11}(SnB11H11)] (4) were determined by X-ray crystal structure analysis; they establish an unprecedented structural motif in the chemistry of heteroboranes and transition-metal fragments with the stanna-closo-dodecaborate moiety as a two-faced ligand that exhibits 1(Sn) as well as 3(BH) coordination. The 3-coordinated stannaborate in 4 and in the isostructural compound [Bu3MeN]2[Ru(PPh3)2{2,7,8-(-H)3-exo-SnB11H11}(SnB11H11)] (5) shows fluxional behavior, which was studied in detail by using 31P{1H} EXSY and DNMR experiments. The activation parameters for the dynamic process of 5 are given.

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[UP]	R. Schmitt, B. Blaschkowski, K. Eichele, H.-J. Meyer: Calcium Tetraboride-Does It Exist? Synthesis and Properties of a Carbon-Doped Calcium Tetraboride That Is Isotypic with the Known Rare Earth Tetraborides Inorg. Chem. 2006, 45, 3067 -3073. DOI 10.1021/ic0518430

Crystalline samples of carbon-doped CaB₄ were synthesized by solid-state reactions in sealed niobium ampules from the elements Ca, B, and C. The structure was determined by single-crystal X-ray diffraction (P4/mbm, Z = 4, a = 7.0989(7) Å, c = 4.1353(5) Å, R1 = 0.026, and wR2 = 0.058) revealing an atom arrangement containing a three-dimensional boron network built up from B₆ octahedra and B₂ dumbbells which is well-known from the structures of rare earth tetraborides. Crystals of CaB_4-xC_x are black with a metallic luster and behave stable against mineral acids. Band structure calculations indicate that CaB₄ is a stable semiconducting compound with a narrow band gap and that carbon should not necessarily be required for the stability of this compound. The presence of carbon in the crystalline samples of CaB_4-xC_x was indicated by electron energy loss spectroscopy, but the carbon content in the samples was estimated to be less than 5% according to inductively coupled plasma-atomic emission spectrometry measurements. The distribution of boron and carbon atoms in the structure was investigated by means of ¹¹B and ¹³C solid-state magic angle spinning NMR. Measurements of the magnetic susceptibility indicate a temperature-independent paramagnetism down to 20 K.

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[UP]	T. Gädt, K. Eichele, L. Wesemann: Bonding Modes of Stanna-closo-Dodecaborate: η1(Sn) to η3(BH) Rearrangement Reactions in Zwitterionic Stanna-closo-Dodecaborate Ruthenium Complexes J. Chem. Soc., Dalton Trans. 2006, 2706-2713. DOI 10.1039/b517138e

Reaction of the stanna-closo-dodecaborate salt [Bu₃MeN]₂[SnB₁₁H₁₁] with the dimeric ruthenium complex [Ru₂(μ-Cl)₃(triphos)₂]Cl (triphos = {MeC(CH₂PPh₂)₃}) in refluxing acetonitrile yields the zwitterionic compound [Ru(SnB₁₁H₁₁)(MeCN)₂(triphos)] (4) which has been characterized by single-crystal X-ray diffraction analysis and solid-state NMR spectroscopy. Refluxing the zwitterion 4 in acetone leads to an η¹(Sn) to η³(BH) rearrangement with formation of [Ru(SnB₁₁H₁₁)(triphos)] (5) whose structure has been confirmed by X-ray diffraction and multinuclear NMR spectroscopy in solution and in the solid state. Furthermore, two isomeric zwitterions fac- and mer-[Ru(SnB₁₁H₁₁)(dppb)(MeCN)₃] (6a, 6b) and their rearrangement reactions as well as their NMR properties are described.

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[UP]	T. Gädt, K. Eichele, L. Wesemann: Bimetallic Zwitterionic Complexes with an Ambident Stanna-closo-dodecaborate Ligand: [1-{M(CO)5}-2,7,8-(μ-H)3-{Fe(triphos)}-SnB11H11] (M = Cr, Mo, W) Organometallics 2006, 25, 3904-3911. DOI 10.1021/om060328m

Starting from FeBr₂ the zwitterionic stannaborate complex [1-{Fe(MeCN)₂(triphos)}-SnB₁₁H₁₁] (1) could be obtained in a straightforward one-pot synthesis. Via a facile η¹(Sn) to η³(BH) rearrangement reaction 1 can be converted into [2,7,8-(μ-H)₃-{Fe(triphos)}-SnB₁₁H₁₁] (2). The nucleophilicity of the tin atom in compound 2 is strongly reduced compared to the dianionic parent stannaborate cluster [SnB₁₁H₁₁]^2-. Methylation at the tin atom using standard methods is not feasible. Transition metal fragments can be coordinated at the tin atom of 2 if reactive species such as M(CO)₅(THF) (M = Cr, Mo, W) are employed. Reaction of these fragments with 2 yields the bimetallic zwitterions [1-{M(CO)₅}-2,7,8-(μ- H)₃-{Fe(triphos)}-SnB₁₁H₁₁] (M = Cr, Mo, W) (3, 4, 5), which contain an ambident stannaborate moiety. All new compounds have been characterized using ¹H, ¹¹B, ¹³C, ³¹P, and ¹¹⁹Sn NMR spectroscopy as well as ³¹P and ¹¹⁹Sn MAS NMR experiments. Single-crystal X-ray diffraction analyses have been carried out for all novel compounds.

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[UP]

N. Kuhn, K. Eichele, M. Steimann, A. Al-Sheikh, B. Doser, C. Ochsenfeld: Wasserstoffbrückenbindungen mit Cyanidionen? Die Strukturen von 1,3-Diisopropyl-4,5-dimethylimidazoliumcyanid und 1-Isopropyl-3,4,5-trimethylimidazoliumcyanid. Z. Anorg. Allg. Chem. 2006, 632, 2268-2275. DOI 10.1002/zaac.200600157

1,3-Diisopropyl-4,5-dimethylimidazolium cyanide (2a) and 1-isopropyl-3,4,5-trimethylimidazolium cyanide (2b) are obtained from the reaction of the corresponding 2,3-dihydrodimethylimidazol-2-ylidenes (1) and hydrogen cyanide in excellent yield. Their crystal structure analyses reveal the presence of ion pairs linked by hydrogen bonds. The crystal structure analysis of 2a reveals a near colinear orientation of the C(1)-H bond axis and the cyanide ion while in 2b this orientation is perpendicular. In both cases, the interionic distances are in the expected range for hydrogen bonds. Ab-initio calculations of the total energy of the salts 2 indicate small differences in energy between the colinear and perpendicular orientation of the ions as well as between the colinear C-H···C-N and C-H···N-C orientations. The comparison of calculated and measured ¹³C and ¹⁵N NMR chemical shifts does not allow the distinction between the possible orientations.