Jörg Grunenberg

Technische Universität Braunschweig, Brunswyck, Lower Saxony, Germany

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Publications (101)447.66 Total impact

  • Jörg Grunenberg
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    ABSTRACT: Is it time to reconsider the whole concept of quadruple bonding? Contrary to the conclusion of Shaik and co-workers in Chem. Eur. J.- 2014, 20, 6220-6232, there is no "deviation of C2 from the Badger Rule".
    No preview · Article · Oct 2015 · Chemistry - A European Journal
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    ABSTRACT: A domino approach consisting of up to five consecutive steps to access either highly substituted dispiranes or π-helicenes from oligoyne chains is reported. The domino sequence consists of several carbopalladation reactions, a Stille cross-coupling to obtain the helicenes, and, depending on the steric demands of the helicene, a final 6π-electrocyclization to afford the dispiranes. Formally, the latter transformation contravenes the Woodward-Hoffmann rules, as revealed by X-ray crystallography of the dispirane. Additionally, the racemization barrier of the (Z,Z,Z)-triene-based helicene has been determined by a kinetic analysis and compared with results from density functional theory calculations. Characteristic points on the reaction coordinate were further analyzed according to their relaxed force constants (compliance constants).
    No preview · Article · Sep 2015 · Chemistry - A European Journal
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    ABSTRACT: Der winteraktive Springschwanz Ceratophysella sigillata produziert einzigartige polychlorierte Octahydroisocumarine um Fressfeinde abzuschrecken. Die Struktur der Hauptverbindung Sigillin A wurde durch Isolierung, spektroskopische Untersuchungen und Röntgenstrukturanalyse aufgeklärt. Sigillin A zeigte in einem Biotest mit räuberischen Ameisen eine hohe abschreckende Wirkung. Ein vielversprechender Syntheseansatz für diese neue Klasse von Naturstoffen wurde entwickelt.
    No preview · Article · May 2015 · Angewandte Chemie
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    ABSTRACT: The snow flea Ceratophysella sigillata, a winter-active species of springtail, produces unique polychlorinated octahydroisocoumarins to repel predators. The structure of the major compound, sigillin A, was elucidated through isolation, spectroscopic analysis, and X-ray crystallography. Sigillin A showed high repellent activity in a bioassay with predatory ants. A promising approach for the total synthesis of members of this new class of natural compounds was also developed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · May 2015 · Angewandte Chemie International Edition
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    Jörg Grunenberg
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    ABSTRACT: In a recent publication in this journal, the interpretation of the Braunschweig’ s diboryne as a true triple bond is questioned. The analysis by Köppe and Schnöckel is based, inter alia, on the calculation of rigid coupling force constants. Nevertheless, since it is known for a long time that the use of rigid force constants as bond strength descriptors is by no means straight forward, we recomputed the rigid force constants for a model diboryne, applying different coordinate systems and compared the values with the relaxed force constants (generalized compliance constants, GCC). In contrast with the results by Schnöckel and Köppe, the true coupling between the boron-boron bond and the boron-carbon bond, that means, after the elimination of all numerical artifacts, is negligible (fBB/BC = -0.003).
    Preview · Article · May 2015 · Chemical Science
  • Laura G. Sarbu · Henning Hopf · Jörg Grunenberg · Lucian M. Birsa
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    ABSTRACT: The reduction of pseudo-geminal bis(ethynyl)-substituted [2.2]paracyclophanes provides compounds with new bridges. The type of bridging is substituent dependent. The (trimethylsilyl)ethynyl moiety induces the formation of a bridge with two semicyclic double bonds; less bulky substituents, like propynyl and phenylethynyl, lead to bridges with endo double bonds.
    No preview · Article · Jan 2015 · Synlett
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    Jörg Grunenberg · Angelo Spinello · Giampaolo Barone
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    ABSTRACT: In depth Monte Carlo conformational scans in combination with molecular dynamics (MD) simulations and electronic structure calculations were applied in order to study the molecular recognition process between tetrasubstituted naphthalene diimide (ND) guests and G-quadruplex (G4) DNA receptors. ND guests are a promising class of telomere stabilizers due to which they are used in novel anticancer therapeutics. Though several ND guests have been studied experimentally in the past, the protonation state under physiological conditions is still unclear. Based on chemical intuition, in the case of N-methyl-piperazine substitution, different protonation states are possible and might play a crucial role in the molecular recognition process by G4-DNA. Depending on the proton concentration, different nitrogen atoms of the N-methyl-piperazine might (or might not) be protonated. This fact was considered in our simulation in terms of a case by case analysis, since the process of molecular recognition is determined by possible donor or acceptor positions. The results of our simulations show that the electrostatic interactions between the ND ligands and the G4 receptor are maximized in the case of the protonation of the terminal nitrogen atoms, forming compact ND G4 complexes inside the grooves. The influence of different protonation states in terms of the ability to form hydrogen bonds with the sugar-phosphate backbone, as well as the importance of mediated vs. direct hydrogen bonding, was analyzed in detail by MD and relaxed force constant (compliance constant) simulations.
    Full-text · Article · Jan 2015 · Physical Chemistry Chemical Physics
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    ABSTRACT: Ein neuartiger Typ von π-Helicenen, deren π-System auf eine all-s-cis-Z,Z,…-Oligoenkette reduziert ist, wird vorgestellt. Eine Dominosequenz aus bis zu vier aufeinanderfolgenden Carbopalladierungen und einer abschließenden Stille-Kreuzkupplung wurde entwickelt, um den einstufigen Aufbau dieser Einheiten ausgehend von den jeweiligen linearen Oligoinen zu ermöglichen. Trotz des minimalen π-Systems wurden für die einzelnen Enantiomere sehr hohe Werte ihrer optischen Rotation festgestellt. Die schraubenförmigen Strukturen wurden durch Röntgenstrukturanalyse zweifelsfrei nachgewiesen.
    No preview · Article · Dec 2014 · Angewandte Chemie
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    ABSTRACT: A novel type of π-helicenes is reported, in which the π-system is truncated to an all-s-cis all-Z oligoene chain. A domino sequence was developed, consisting of up to four consecutive carbopalladation reactions and a terminal Stille cross-coupling, to generate these entities in one step from the respective linear oligoynes. Despite the minimal π-system, very high optical rotation values were encountered for the single enantiomers. X-ray crystallography confirmed their screw-shaped structure. (Chemical Equation Presented).
    No preview · Article · Dec 2014 · Angewandte Chemie International Edition
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    ABSTRACT: The [2.2]paracyclophane moiety is used as a spacer to connect the ends of a hex-3-ene-1,5-diyne unit, a π-system that on thermolysis usually cycloaromatizes to a benzene ring (Bergman cyclization). For the preparation of the pseudo-geminally-bridged system 9, the diacetylene 3 was chain-extended to the diol 16, which after conversion to the pseudo-geminal dibromide 17 was ring-closed by treatment with LiHMDS/HMPA to the [2.2]paracyclophane enediyne 9. Whereas the McMurry coupling of the pseudo-ortho bisaldehyde 24 resulted in the formation of the hexadienyne-bridged cyclophane 27, the pseudo-ortho-bridged hydrocarbon 11 was obtained by preparing first the diol 28 from 24, converting the latter into the dioxolane 29, which in the last step furnished the olefin 11 by treatment with Tf2O/EtN(iPr)2. The authentic Bergman product 10 of the pseudo-gem-bridged hexenediyne 9 was synthesized by a conventional sequence starting from the ethynyl formyl substrate 18. Since the pseudo-ortho-enediyne-bridged hydrocarbon 11 is thermally labile, its benzannelated derivate 34 was prepared. No classical Bergman cyclization reactions could be observed for any of the [2.2]paracyclophane-bridged hexenediynes prepared here. In the pseudo-gem-series the fulvenes 14 and 15 were the only products that could be identified under thermal conditions (McMurry coupling); the benzannelated substrate 34 gave the benzofulvene-bridged cyclophane 36 on photolysis. Bergman cyclizations yielding fulvene derivatives are extremely rare. The mechanism of the cyclization of 9 and 34 is discussed, using compliance constants. The structure assignments of the hydrocarbons synthesized in this study are based on spectroscopic studies as well as X-ray structural analyses for 9, 10, 11, 27, and 34.
    No preview · Article · Dec 2014 · Chemistry - A European Journal
  • Jörg Grunenberg · Giampaolo Barone · Angelo Spinello
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    ABSTRACT: Different force fields and approximate density functional theory were applied in order to study the rotamer space of the telomeric G-quadruplex DNA. While some force fields show an erratic behavior when it comes to the reproduction of the higher-order DNA conformer space, OPLS and MMFF implementations are able to reproduce the experimentally known energy order. The stabilizing effect of the AA (anti−anti) versus SA (syn−anti) conformer is analyzed applying mechanical bond strength descriptors (compliance constants). The fact that we observe the correct energy order using appropriate force fields is in contrast with results previously reported, which suggested the general inappropriateness of force fields for the description of G-quadruplex structures.
    No preview · Article · Aug 2014 · Journal of Chemical Theory and Computation
  • Christian Kleeberg · Jörg Grunenberg · Xiulan Xie
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    ABSTRACT: A series of trimethylstannyl potassium complexes [K(L)SnMe3] with different auxiliary ligands L (L = 18-C-6, (TMEDA)2 (TMEDA = tetramethylethylenediamine), and (12-C-4)2) were synthesized by alkoxide-induced B-Sn bond cleavage. X-ray structure determinations were performed for all these complexes, and the structural chemistry was studied in detail. For L = 18-C-6 and (TMEDA)2 the solid state structures comprise polymeric [K(L)SnMe3]n chains containing bidentate trimethylstannyl anions bridging two [K(L)](+) ions, featuring unsymmetrical coordination of the [K(L)](+) ion by K-Sn and K-H3C interactions as a central structural motif. In contrast, for L = (12-C-4)2, separated [K(12-C-4)2](+) and [SnMe3](-) ions are observed. Unexpectedly, in the presence of tetrahydrofuran (THF), [K(18-C-6)SnMe3]n forms upon crystallization a new species consisting of separated [K(18-C-6)(THF)2](+) and [(Me2SnCH3)K(18-C-6)SnMe3](-) ions. In this unsymmetrical anion two trimethylstannyl anions coordinate a single [K(18-C-6)](+) ion; one trimethylstannyl anion coordinates via a K-Sn interaction, and the second coordinates via a K-H3C interaction. Simulations of the mechanochemical properties (compliance constants) applying approximated density functional theory revealed that both interactions are very soft and are of comparable strength. Moreover, according to our gas phase simulations the unsymmetrically coordinated [(Me2SnCH3)K(18-C-6)SnMe3](-) is indeed thermodynamically favored over both possible symmetrical isomers with either K-Sn or K-H3C coordination. Furthermore, the existence of multiple species due to the two coordination modes and aggregates of [K(18-C-6)SnMe3] in solution is suggested by NMR spectroscopic studies using (1)H, NOESY/ROESY, and (1)H pulsed field gradient diffusion experiments.
    No preview · Article · Apr 2014 · Inorganic Chemistry
  • Georgios Markopoulos · Jörg Grunenberg
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    ABSTRACT: Determining the weakest link: A simple analysis pinpoints kinetically unstable carbon-carbon bonds. No prior knowledge of reaction pathways is necessary and the approach is particularly helpful for the prediction of novel molecules. krel =relaxed force constant, req =bond length.
    No preview · Article · Sep 2013 · Angewandte Chemie International Edition
  • Georgios Markopoulos · Jörg Grunenberg
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    ABSTRACT: Achillessehne auf den ersten Blick: Wir stellen eine einfache Analyse vor, die kinetisch labile Kohlenstoff‐Kohlenstoff‐Bindungen anzeigt. Detaillierte Kenntnisse über Reaktionsmechanismen sind a priori nicht notwendig, und die Methode ist besonders nützlich bei der Vorhersage von neuen Molekülen. k rel=relaxierte Kraftkonstante, r eq=Bindungslänge.
    No preview · Article · Sep 2013 · Angewandte Chemie
  • Holger F. Bettinger · Sarah Brough · Jörg Grunenberg
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    ABSTRACT: The interaction of methyl(oxo)borane, CH3BO, with typical Lewis bases (nitrogen based and N‐heterocyclic carbenes) was investigated using density functional theory (B97‐D, TPSS‐D3), double hybrid density functionals (PWPB95‐D3, B2PLYP‐D3) in conjunction with empirical dispersion corrections, and coupled cluster theory involving singles, doubles, and a perturbative estimate of triple excitations [CCSD(T)]. A polarized quadruple‐zeta basis set was used throughout. The interaction energies computed with the double‐hybrid methods agree very well with CCSD(T). Compared to typical boron Lewis acids, the interaction energies are much smaller for methyl(oxo)borane, indicating that the BO triple bond results in significantly reduced Lewis acidity. An analysis of the mechanical bond strengths in CH3BO and its complexes indicates that the relaxed BO force constants (compliance constants) and the stretching vibrations decrease with increasing strengths of the dative interactions.
    No preview · Article · Jun 2013 · Zeitschrift für anorganische und allgemeine Chemie
  • Jörg Grunenberg · Giampaolo Barone
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    ABSTRACT: Just as the potential energy can be written as a quadratic form in internal coordinates, so it can also be expanded in terms of generalized forces. The resulting coefficients are termed compliance constants. In this article, the suitability of compliance constants as non-covalent bond strength descriptors is studied (a) for a series of weakly bound hydrogen halide–rare gas complexes applying a configuration interaction theory, (b) for a double stranded DNA 4-mer using approximate density functional methods and finally (c) for a double stranded DNA 20-mer using empirical force fields. Our results challenge earlier studies, which concluded the inappropriateness of compliance constants as soft matter descriptors. The discrepancy may be ascribed, inter alia, to the application of an oversimplified potential function in these earlier studies, assuming a central forces approximation.
    No preview · Article · Apr 2013 · RSC Advances
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    ABSTRACT: A bridging chloride anion between two electrophilic phosphorus centers was observed for the first time in the molecular structure of the novel P–P bonded cation [LDipp2P2Cl3]+ (2+; LDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Cation 2+ is prepared by the reduction of the monophosphorus species [LDippPCl2]+ (1+) with sodium. DFT calculations, AIM and mechanochemical (compliance constants) analyses are used to examine the bonding situation of this unusual species. The monochloro-substituted cation [LDipp2P2Cl]+ (3+) was likewise observed as a reduction product of 1+.
    No preview · Article · Apr 2013 · Organometallics
  • Thies M. Schulze · Jörg Grunenberg · Stefan Schulz
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    ABSTRACT: The synthesis of α-methyl-β-hydroxy-δ-trichloromethyl-δ-valerolactone was achieved by an intramolecular Reformatsky reaction. The cyclisation was effected by samarium diiodide or (for the first time) ytterbium diiodide. The diastereoselectivity of the reaction corresponds to earlier investigations by Molander. Consecutive stereoselective reactions during the esterification to the Reformatsky precursor 1,1,1-trichloropent-4-en-2-yl 2-bromopropanoate and in the Reformatsky reaction itself led to (3RS,4RS,6SR)-4-hydroxy-3-methyl-6-(trichloromethyl)tetrahydro-2H-pyran-2-one (3a) as the major formed diastereomer. The influence of the orientation of the substituents in the transition state is discussed.
    No preview · Article · Feb 2013 · Tetrahedron Letters
  • Jörg Grunenberg
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    ABSTRACT: Determining molecular bond orders can be a delicate and sophisticated task, especially if the electronic structure of the studied system is complex. Now, two different ab initio methods have revealed that C2 and analogous species have a fourth bond, rather than the previously assumed maximum of three.
    No preview · Article · Feb 2012 · Nature Chemistry
  • Marc D. Walter · Jörg Grunenberg · Peter S. White
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    ABSTRACT: Metathesis of [Cp′FeI]2 (1) with KHBEt3 affords the polyhydride iron complexes [Cp′FeH2]2 (2) and [Cp′2Fe2H3] (3). The ratio in which both 2 and 3 are obtained correlates to the applied H2 pressure during synthesis. Complex 2 activates CH- or CD- bonds in aromatic compounds and shows slow H/D exchange in the presence of D2 at room temperature in cyclohexanesolvent. [Cp′FeH2]2 acts as a Cp′Fe(I)-synthon when reacted with white phosphorus (P4) to give [Cp′Fe]2(μ-P4) (4) as the only P-containing product. This complex is best described as a triple-decker complex with a planar arrangement of a severely distorted kite-like cyclo-P4 unit. This distortion persists in solution and solid state as evidenced by a small PP coupling constant in the 31P{1H} NMR spectrum and a long P–P distance of 2.53 Å. Complex 4 is an isomer to the long-known [{Cp′Fe}2(μ-η4:η4-P4)] (5) with a cis-tetraphosphabutadiene moiety and it thermally rearranges to 5, [{Cp′Fe}2(μ-η3:η3-P3)] and [Cp′Fe(P5)]. All complexes described in this paper have been completely characterized including X-ray crystallography, variable temperature NMR studies and DFT calculations. Relaxed force constants (inverse compliance constants) are used as bond strength descriptors.
    No preview · Article · Oct 2011 · Chemical Science