Gregor Schnakenburg

University of Bonn, Bonn, North Rhine-Westphalia, Germany

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Publications (178)794.08 Total impact

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    ABSTRACT: From enantiomerically pure, planar chiral [2.2]paracyclophane amines a series of nitrogen acyclic carbenegold(I) complexes and nitrogen heterocyclic carbenegold(I) complexes are prepared by a modular template synthesis using isonitriles and amines. These chiral catalysts are tested in two reactions, the enantiotopos-selective furanyne cyclization and the enantioselective enyne cyclization. While excellent conversions could be achieved with these new catalysts, the enantioselectivities in only some cases are in the range of best known catalysts for these conversion.
    Journal of Organometallic Chemistry 03/2015; DOI:10.1016/j.jorganchem.2015.03.010 · 2.30 Impact Factor
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    ABSTRACT: Reaction of a Li/Cl phosphinidenoid complex with N,N'-dialkyl carbodiimides yielded the novel 3-imino-azaphosphiridine complexes; reaction with water led selectively to the first stable valence isomer of an oxaphosphirane complex.
    Chemical Communications 02/2015; 51(18). DOI:10.1039/c4cc10266e · 6.72 Impact Factor
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    ABSTRACT: The novel N,P,C-cage complexes 5 a–f and 6 a–f have been obtained by the reaction of the P-pentamethylcyclopentadienylphosphinidene complex 2, generated thermally from 2H-azaphosphirene complex 1, with N-methyl-C-arylcarbaldimines 3 a–f. Li/Cl phosphinidenoid complex 8 reacted with 3 a,b to give N,P,C-cage complexes 6 a,b, whereas with 3 c–f, complexes 6 c–f were obtained in negligible amounts only. Both types of ligand N,P,C-cage structures 5 and 6 were found to be in an unprecedented equilibrium, with 5 a,f as the predominant species. Transient electrophilic terminal phosphinidene complexes 10 a–f serve as intermediates in both ligand interconversions (5 a,f6 a,f), as evidenced through trapping reactions with phenylacetylene and N-methyl-C-phenylcarbaldimine, thus leading to the novel N,P,C-cage complexes 13 b and 15. DFT calculations predicted a small difference in the relative energies of the two types of N,P,C-cage ligands, and a remarkable stabilisation of the aminophosphinidene complex 10 as the common precursor, thereby providing an insight into this surprising 5-ring–3-ring interconversion. In depth analysis of intermediate 10 revealed the occurrence of both through-bond (conventional inductive/mesomeric effects) and through-space (non-covalent interactions) mechanisms, which amount to 67.8 and 14.4 kcal mol−1, respectively, and account for the remarkable stabilisation of this intermediate.
    Chemistry - A European Journal 01/2015; 21(9). DOI:10.1002/chem.201405754 · 5.93 Impact Factor
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    ABSTRACT: An experimental and theoretical study of the first compound featuring a SiP bond to a two-coordinate silicon atom is reported. The NHC-stabilized phosphasilenylidene (IDipp)SiPMes* (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, Mes*=2,4,6-tBu3C6H2) was prepared by SiMe3Cl elimination from SiCl2(IDipp) and LiP(Mes*)SiMe3 and characterized by X-ray crystallography, NMR spectroscopy, cyclic voltammetry, and UV/Vis spectroscopy. It has a planar trans-bent geometry with a short SiP distance of 2.1188(7) Å and acute bonding angles at Si (96.90(6)°) and P (95.38(6)°). The bonding parameters indicate the presence of a SiP bond with a lone electron pair of high s-character at Si and P, in agreement with natural bond orbital (NBO) analysis. Comparative cyclic voltammetric and UV/Vis spectroscopic experiments of this compound, the disilicon(0) compound (IDipp)SiSi(IDipp), and the diphosphene Mes*PPMes* reveal, in combination with quantum chemical calculations, the isolobal relationship of the three double-bond systems.
    Angewandte Chemie International Edition 01/2015; 127(9). DOI:10.1002/anie.201411264 · 11.34 Impact Factor
  • Andreas Eich, Gregor Schnakenburg, Johannes Beck
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    ABSTRACT: Colorless, highly hygroscopic crystals of the title compound are synthesized from a mixture of Sb, SbCl3, Sb2O3, GaCl3, and Te (glass ampule, Ar, 6 x 10-2 mbar, 50 °C, 19 d).
    ChemInform 01/2015; 46(1):no-no. DOI:10.1002/chin.201501013
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    ABSTRACT: InFeO3(ZnO)4 was prepared from binary oxides as starting materials at 1350 °C in sealed platinum tubes as an earth brown powder. Single crystals were grown from a K2MoO4 flux in sealed Pt-tubes using cooling rates of –0.1 K min–1. The structure of InFeO3(ZnO)4 was refined in space group P63/mmc; No. 194 (a = 3.211(6) Å; c = 33.032(6) Å; Z = 2; R1 = 3.68 %) from XRD data and revealed a build-up from alternate stacking of layers of edge-sharing InO6 octahedra and 5 layers of corner-sharing (Zn/Fe)O4 tetrahedra. Inversions of the (Zn/Fe)O4 tetrahedra occurs (i) at the InO6 octahedral layer and (ii) halfway in the wurtzite type region where the inversion boundary is built by cations in 4+1 trigonal bipyramidal coordination. The position of the cations in their oxygen surrounding is described by a factor t which quantifies the displacement of the cation from the center of a trigonal bipyramid towards one of the constituting tetrahedra. Refining the site occupation factors of the cations in the (Zn/Fe)O4 tetrahedra results in a clear and reasonable gradient for the distribution of iron. Refinement of the oxygen position reveals split positions for the oxygen atoms at the second inversion boundary in the center of the wurtzite type region which shows similarities to inversion domain boundaries at fivefold coordinated cations in the wurtzite type region of compounds of type ARO3(ZnO)m with m > 15. Thus, it is more likely to describe InFeO3(ZnO)4 as a closest-packed structure of cations with oxygen filling the interstices.
    Zeitschrift für anorganische Chemie 11/2014; 640(14). DOI:10.1002/zaac.201400372 · 1.25 Impact Factor
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    ABSTRACT: The synthesis and structures of RhI and IrI complexes bearing 4-phosphinoyl- and 4,5-bis(phosphinoyl)imidazol-2-ylidene ligands (NHCP) is reported. Deprotonation of the corresponding imidazolium hydrogen sulfate salts by KOtBu in the presence of [M(cod)Cl]2 afforded complexes of the formula [M(cod)Cl(NHCP)] [5a/5b: NHCP = 4-Ph2P(O)-IiPrMe, 5a: M = Rh, 5b: M = Ir and 7a/7b: NHCP = 4,5-{Ph2P(O)}2-InBuMe]. The RhI complexes 5a and 7a were then converted into [Rh(CO)2Cl(NHCP)] 8a and 9a via reaction with carbon monoxide; the average CO stretching frequencies [8a: (CO)av = 2036 cm–1 and 9a: (CO)av = 2038.4 cm–1] led to the conclusion that mono- and bis-functionalized NHCPs act as relatively weaker donors than backbone unsubstituted NHC. A first examination of Janus-head ligand properties of complex 7a revealed that reaction with TiCl4 afforded hetero-dinuclear 10a,a′ as a mixture of isomeric monodentate phosphinoyl titanium(IV) adducts. All products were characterized by elemental analyses, spectroscopic and spectrometric methods and, in addition, complexes 7a and 7b by single-crystal X-ray structure analysis.
    Berichte der deutschen chemischen Gesellschaft 10/2014; 2014(29). DOI:10.1002/ejic.201402440 · 2.97 Impact Factor
  • Paresh Kumar Majhi, Gregor Schnakenburg, Rainer Streubel
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    ABSTRACT: Synthesis of the first P(V)-bridged bis(NHC) ligand 7 was achieved via deprotonation of P(V)-functionalized bis(imidazolium) salt 6, which was obtained via oxidative desulfurization of bis(imidazole-2-thion-4-yl)-phosphane 2. Bis(imidazolium) salt 6 was also employed to synthesize the corresponding silver complex 8. All new products were firmly established by spectroscopic and spectrometric methods as well as elemental analysis and, in addition, X-ray crystal structure analysis in the case of 3.
    Dalton Transactions 09/2014; 43(44). DOI:10.1039/C4DT02479F · 4.10 Impact Factor
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    ABSTRACT: Während PV-1,2-Oxaphosphetane von der Wittig-Reaktion her geläufig sind, waren die PIII-Analoga bisher unbekannt. Wir präsentieren hier die Synthese und Reaktionen der ersten 1,2-Oxaphosphetankomplexe, die durch Reaktion des Phosphinidenoidkomplexes [Li(12-Krone-4)(Lsgm)][(OC)5W{(Me3Si)2HC-PCl}] mit unterschiedlichen Epoxiden erhalten wurden. Die Titelverbindungen sind in Toluol bis ca. 100 °C stabil, bevor eine unselektive Zersetzung eintritt. Die säureinduzierte Ringerweiterung mit Benzonitril führt zur selektiven Bildung des ersten Komplexes mit einem 1,3,4-Oxazaphosphacyclohex-2-en-Liganden.
    Angewandte Chemie 09/2014; 126(40). DOI:10.1002/ange.201404877
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    ABSTRACT: While PV 1,2-oxaphosphetanes are well known from the Wittig reaction, their PIII analogues are still unexplored. Herein, the synthesis and reactions of the first 1,2-oxaphosphetane complexes are presented, which were achieved by reaction of the phosphinidenoid complex [Li(12-crown-4)(solv)][(OC)5W{(Me3Si)2HCPCl}] with different epoxides. The title compounds appeared to be stable in toluene up to 100 °C, before unselective decomposition started. Acid-induced ring expansion with benzonitrile resulted in selective formation of the first complex bearing a 1,3,4-oxazaphosphacyclohex-2-ene ligand.
    Angewandte Chemie International Edition 09/2014; 53(40). DOI:10.1002/anie.201404877 · 11.34 Impact Factor
  • Andreas Eich, Gregor Schnakenburg, Johannes Beck
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    ABSTRACT: Gallium antimony chloride oxide, Ga2SbCl7O, is formed in a GaCl3-based melt containing tellurium, antimony, SbCl3, and Sb2O3 in form of colorless, highly hygroscopic crystals. The crystal structure consists of discrete molecules, in which a bent SbOCl unit is coordinated by two GaCl3 groups. The Ga atoms coordinate the oxygen atom, resulting in a planar [Ga2SbO] central building unit. A distinct stereochemical lone pair effect is present at the antimony atom. In the crystal, the molecules are packed in the motif of a hexagonal closest packing. DFT calculations and NBO considerations show that the low lying molecular orbital comprising the lone pair at the oxygen atom emerges from a pure p orbital showing almost no delocalization and no steric effect.
    Zeitschrift für anorganische Chemie 09/2014; 640(12-13). DOI:10.1002/zaac.201400260 · 1.25 Impact Factor
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    ABSTRACT: Open-shell phosphanyl complexes (OC)5W{(Me3Si)2HCP(X)} (X = F, H), obtained by one-electron oxidation of lithium phosphanido complexes, were trapped by TEMPO to yield novel thermally labile P-nitroxyl phosphane complexes. First experimental evidence for an open-shell P-F phosphanoxyl complex (OC)5W{(Me3Si)2HCP(O)F}, formed upon thermolysis of corresponding P-nitroxyl derivative, is reported; reaction pathways are also theoretically investigated.
    Chemical Communications 09/2014; 50(83). DOI:10.1039/C4CC06084A · 6.38 Impact Factor
  • ChemInform 09/2014; 45(35):no-no. DOI:10.1002/chin.201435018
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    ABSTRACT: A novel method for the synthesis of 1H-siloles is presented. It involves a [2+2+1] cycloaddition of the ynediamines R2 NCCNR2 (R=Me, Et) with SiI2 (Idip) (Idip=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) to afford the orange-colored, highly water-sensitive 1,1-diiodo-2,3,4,5-tetraamino-1H-siloles SiI2 {C4 (NR2 )4 } (1-I: R=Me; 2-I R=Et). Treatment of 2-I with an excess of SiBr4 afforded after I/Br exchange the 1,1-dibromo-1H-silole SiBr2 {C4 (NEt2 )4 } (2-Br). The 1H-siloles 1-I, 2-I, and 2-Br were fully characterized and their molecular structures determined by single-crystal X-ray diffraction. The compounds feature a slightly twisted five-membered silacyclopenta-2,4-diene ring and a double/single CC bond alternation in the diene fragment. Reaction of 2-I with the N-heterocyclic carbene IMe4 (IMe4 =1,3,4,5-tetramethylimidazolin-2-ylidene) leads, after displacement of the iodide groups, to the unprecedented diiodide salt [Si(IMe4 )2 {C4 (NEt2 )4 }](I)2 (3), containing a 1H-silole dication with a four-coordinate Si(IV) center. The crystal structure of 3 reveals similar bonding characteristics for the dicationic 1H-silole to those of the neutral 1H-siloles 1-I-2-Br. Two-electron reduction of 3 with C8 K affords, after elimination of one IMe4 group, the thermolabile, carbene-stabilized 1-silacyclopentadien-1-ylidene Si{C4 (NEt2 )4 }(IMe4 ) (4), which was characterized by elemental analysis and (1) H, (13) C{(1) H}, and (29) Si{(1) H} NMR spectroscopies.
    Chemistry 07/2014; 20(30). DOI:10.1002/chem.201403108 · 5.70 Impact Factor
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    ABSTRACT: The oxidative cyclization reaction of 2-aryl cinnamates and derivatives thereof can be easily performed with MoCl5 as the oxidant. This powerful reagent allows oxidative coupling reactions for which other reagents fail. The best results are obtained when the 2-phenyl substituent of the cinnamate is equipped with two methoxy groups. Even iodo moieties in the bay region of phenanthrene are tolerated under the reaction conditions. If naphthalene moieties are involved, a rearrangement of the skeleton occurs, providing an elegant route to highly functionalized angular arenes. The cyclization is demonstrated for 15 example substrates with isolated yields of up to 99 % for the phenanthrene derivative. The broad scope of the reaction underlines the usefulness of MoCl5 and MoCl5/TiCl4 in the oxidative coupling reaction.
    Chemistry - A European Journal 07/2014; 20. DOI:10.1002/chem.201403442 · 5.93 Impact Factor
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    ABSTRACT: The reactions of elemental antimony, tellurium, selenium and sulfur as well as antimony telluride and antimony sulfide in melts composed of GaCl3/SbCl3/ACl (A = Cu+, Ag+, PPh4+) yielded Ag(Sb7Te8)[GaCl4]6 (1), (Sb7Se8)[GaCl4]2[Ga2Cl7]3 (2), (Sb7Se8Cl2)[GaCl4]3 (3) and (Sb7S8Cl2)[GaCl4]3 (4). SbCl3 plays the role of the oxidant, and GaCl3 plays the role of the Lewis acidic chloride ion acceptor. All of the compounds form orange, air-sensitive crystals. The crystal structures consist of discrete, double-cube-shaped, mixed antimony–chalcogen cationic clusters (Sb7Te8)5+, (Sb7Se8)5+, (Sb7Se8Cl2)3+ and (Sb7S8Cl2)3+. The anions are discrete chloridogallate [GaCl4]– and [Ga2Cl7]– anions. All compounds were characterized by single-crystal X-ray diffraction, energy-dispersive electron-beam X-ray fluorescence spectroscopy, Raman vibrational spectroscopy and solid-state 77Se NMR spectroscopy. Supporting gas-phase and periodic DFT calculations allowed the assignments of the spectra and provided insights into the bonding situation of the hypervalent Sb atoms.
    Berichte der deutschen chemischen Gesellschaft 07/2014; 2014(19). DOI:10.1002/ejic.201402230 · 2.97 Impact Factor
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    ABSTRACT: Single crystals of InGaZnO4 were synthesized in a sealed Pt-tube at elevated temperatures under normal pressure without flux. InGaZnO4 has a trigonal crystal system (R (3) over bar mn: No.166) deduced from convergent beam electron diffraction (CBED). Single crystal structure refinement from XRD data at -150 degrees C (a=3275(1) angstrom; c=25.99(1) angstrom; Z = 3) revealed an alternate stacking of InO6/3- and (Ga, Zn)O-4/4(+) layers, iso-structural to YbFe2O4. The cell parameters at room temperature were refined from powder X-ray diffraction data (a=3284(3) angstrom and c=26.037(3) angstrom). The transparent crystals have a gray-bluish color and exhibit an excess of Ga expressed by the cation ratio of In:Ga:Zn=302(9):39(1):31(1) determined by energy dispersive X-ray spectroscopy (EDXS). While the isovalent substitution of In3+ by Ga3+ is known, an additional aliovalent substitution of Zn2+ by Ga3+ is observed. This results in the formula (In0.9Ga0.1)Ga1.06Zn0.91 square O-0.03(4) where 3% of the cations in 4+1 coordination are vacant due to aliovalent substitution. Further evidence of that defect structure is found in the lattice parameter a which is substantially smaller than in stoichiometric InGaZnO4, as well as in the strong absorption in the near-IR from transitions correlated with the defect structure. The bluish color of the crystals is due to an enhanced absorption in the red of the visible spectrum. For the first time, we achieved to image InGaZnO4 at atomic resolution in the electron microscope proving a perfect periodic stacking of atomic layers.
    Journal of Solid State Chemistry 07/2014; 215:176–183. DOI:10.1016/j.jssc.2014.03.042 · 2.20 Impact Factor
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    ABSTRACT: Despite the fact that functionalized planar chiral [2.2]paracyclophanes have received a lot of attention, the chemistry of pseudo-meta 4,15-distubstituted [2.2]paracyclophanes is largely unexplored. This is mainly due to the fact that the 4,5-dibromo-functionalized [2.2]paracyclophane is much less prone to halogen-metal exchange reactions than its constitutional pseudo-ortho or pseudo-para isomers. Here, we give an account of an efficient protocol to achieve this, which allows the synthesis of a broad variety of 4,15-disubstituted [2.2]paracyclophanes. Furthermore, we were able to resolve several of the racemic compounds via chiral HPLC and assign the absolute configurations of the isolated enantiomers by X-ray diffraction and/or by the comparison of calculated and measured CD-spectra.
    The Journal of Organic Chemistry 06/2014; 79(14):6679-6687. DOI:10.1021/jo501212t · 4.64 Impact Factor
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    ABSTRACT: The reaction of Li/Cl P-CPh3 phosphinidenoid tungsten(0) complex 2 with dimethylcyanamide afforded tricyclic phosphirane complex 4, an unprecedented rearrangement of which led to the novel N,P,C cage complex 6. On the basis of DFT calculations, formation and intramolecular [3+2] cycloaddition of the transient nitrilium phosphane ylide complex 3 to a phenyl ring of the triphenylmethyl substituent to give 4 is proposed. Furthermore, theoretical evidence for terminal N-amidinophosphinidene complex 7, formed by [2+1] cycloelimination from 4, is provided, and the role of the electronic structure and non-covalent interactions of intermediate 7 discussed.
    Chemistry - A European Journal 06/2014; 20(23). DOI:10.1002/chem.201305061 · 5.93 Impact Factor
  • European Journal of Inorganic Chemistry 05/2014; 2014(15):n/a-n/a. DOI:10.1002/ejic.201490071 · 2.97 Impact Factor

Publication Stats

1k Citations
794.08 Total Impact Points

Institutions

  • 2006–2015
    • University of Bonn
      • Institute for Inorganic Chemistry
      Bonn, North Rhine-Westphalia, Germany
  • 2010–2012
    • Johannes Gutenberg-Universität Mainz
      • Institute of Organic Chemistry
      Mayence, Rheinland-Pfalz, Germany
  • 2002–2008
    • Humboldt-Universität zu Berlin
      • Department of Chemistry
      Berlín, Berlin, Germany