Klaus Eichele Publication Abstracts 2014

 

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[UP]	H. Scheel, J. Wiederkehr, K. Eichele, H. A. Mayer, F. Winter, R. Pöttgen, L. Wesemann: Dinuclear copper complexes: coordination of Group 14 heteroborates Dalton Trans. 2014, 43(31), 11867-11876. DOI 10.1039/c4dt01242a

Dicopper(I) complexes with the chelating dmapm ligand [dmapm = 1,1-bis{di(o-N,N-dimetylanilinyl)phosphino}methane] have been synthesized and characterized structurally. Synthesis of the acetonitrile adduct [Cu₂(µ-dmapm)(CH₃CN)₂][BF ₄]₂ (1) has been presented and the dicopper electrophile has been used as the starting material in reaction with Group 14 heteroborates. Coordination of the closo-borates at the dicopper moiety resulted in different molecular structures with varying Cu...Cu distances. In the case of the side on coordinated stanna-closo-dodecaborate the tin vertex has been characterized by ¹¹⁹Sn Mössbauer spectroscopy and the nucleophilicity at the tin was established in reaction with a molybdenum carbonyl complex.

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[UP]	N. Dettenrieder, C. O. Hollfelder, L. N. Jende, C. Maichle-Mössmer, R. Anwander: Half-Sandwich Rare-Earth-Metal Alkylaluminate Complexes Bearing Peripheral Boryl Ligands Organometallics 2014, 33(7), 1528–1531. DOI 10.1021/om401163a

[(C₅Me₅)LnMe₂]₃ (Ln = Y, Lu) dissolve readily in a n-hexane/toluene mixture upon addition of 3 equiv of the organoaluminum boryl compound [Me₂Al{B(NDippCH)₂}]₂ (Dipp = C₆H₃iPr₂-2,6). The half-sandwich complexes (C₅Me₅)Ln[(AlMe₃){B(NDippCH)₂}]₂ thus formed display unsymmetrical heteroaluminate coordination not only in the solid state but also at lower temperatures in solution, which is distinct from the behavior of the homoaluminate congeners (C₅Me₅)Ln(AlMe₄)₂. The effect of homo- versus heteroaluminate coordination is assessed in the coordinative polymerization of isoprene.

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[UP]	J. Henning, K. Eichele, R. F. Fink, L. Wesemann: Structural and Spectroscopic Characterization of Tin–Tin Double Bonds in Cyclic Distannenes Organometallics 2014, 33(14), 3904–3918. DOI 10.1021/om500645b

Three cyclic distannenes, 1, 3, and 4, and one spacer-bridged bis(stannylene), 2, were prepared and thoroughly investigated by single-crystal X-ray diffraction in the solid state, by variable-temperature (VT) ¹¹⁹Sn NMR, VT ¹H NMR, ¹³C NMR, and UV–vis spectroscopy in solution, and by quantum chemical calculations. The tin(II) compounds feature rigid 9,9-dimethylxanthene or naphthalene backbones and very bulky m-terphenyl substituents Ar^R [=C₆H₃-2,6-{C₆H₂-2,4,6-R₃}₂; R = Me (1, 3), i-Pr (2, 4)]. For distannenes 3 and 4, the strain of the naphthalene backbone results in rather short tin–tin distances of 2.7299(3) and 2.7688(2) Å, respectively, whereas the xanthene backbone produces long tin–tin distances of 3.0009(7) Å for distannene 1 and 4.2779(7) Å for the spacer-bridged bis(stannylene) 2. In comparison to the Ar^iPr substituents, the less bulky Ar^Me substituents give rise to stronger trans-bending of the distannenes; moreover, DFT calculations indicate that, in contrast to Ar^iPr, the Ar^Me substituents allow for asymmetric distortion of the trans-bending in dynamic processes. The oxidation products of distannene 1 and bis(stannylene) 2 reveal rare structural motifs: dihydroxydistannoxane 5 and bis(dihydroxystannane) 6, respectively, which feature terminal Sn–OH functionalities. The reaction of distannene 1 with 1 equiv of potassium chloride in the presence of the cryptating agent 222 results in the formation of the unusual stannyl stannide 7. A modified synthesis protocol for the preparation of distannene 1 yields in one step the stannyl stannylene 8 with a center of chirality at the stannyl tin atom. The series 1, 7, and 8 represents a variation of electronic tin–tin interactions.

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[UP]	M. Göhner, F. Herrmann, K. Eichele, H. F. Bettinger, M. Ströbele, N. Kuhn: Die Strukturchemie der 2-Chalkogeno-1,3,4,5-tetraisopropylimidazoline Z. Naturforsch. B 2014, 69, 1384–1394. DOI 10.5560/ZNB.2014-4189

1,3,4,5-Tetraisopropyl-2-thioimidazoline (6b) was prepared by condensation of N,N'-diisopropylthiourea and isobutyroin. 1,3,4,5-Tetraisopropyl-2-oxoimidazoline (6a), 1,3,4,5-tetraisopropyl-2-selenoimidazoline (6c) and 1,3,4,5-tetraisopropyl-2-telluroimidazoline (6d) were obtained from 2,3-dihydro-1,3,4,5-tetraisopropylimidazol-2-ylidene and dinitrogen oxide or selenium and tellurium, respectively. The crystal structure analyses revealed the presence of the A-type rotamer for 6a while for 6c a paddlewheel-like orientation of the isopropyl substituents was found (I type). In crystals of 6b, both A- and E-type molecules are present while in solution at room temperature the I-type rotamer is detected. A dynamic ¹H and ¹³C{¹H} NMR study of 6b in the range of 185.5 to 423.3 K revealed a temperature-dependent rotation of the isopropyl substituents (ΔH^† = 15.7(9) kcal mol^-1, ΔS^† = -5(3) cal K^-1 mol^-1, ΔG^† = 17.2(9) kcal mol^-1) with I as the rotamer of lowest energy. This result is confirmed by MO calculations which indicate A and C being the next stable rotamers. The barrier of rotation of the isopropyl substituents about the C–N bond from I to C (B3LYP ΔH^† = 13.7 kcal mol^-1, ΔG^† = 15.4 kcal mol^-1) is slightly lower than that about the C–C bond from I to G.