Gregor Schnakenburg

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

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Publications (123)634.47 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: Two bis(3-pyridyl) ligands 1 and 2 based on a planar chiral [2.2]paracyclophane scaffold were synthesized in enantiomerically pure forms. These ligands act as trans-chelating ligands for square-planar-coordinated metal centres such as palladium(II) ions. Upon forming mononuclear homochiral [ML2] complexes, they show complete chiral self-sorting in a narcissistic self-recognition manner as proven by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction.
    Berichte der deutschen chemischen Gesellschaft 04/2014; · 2.94 Impact Factor
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    ABSTRACT: An Li/Cl phosphinidenoid complex, obtained by chlorine/lithium exchange from a [dichloro(organo)phosphane]tungsten(0) complex, reacted with aliphatic dicarbonyl derivatives to provide oxaphosphirane complexes, a 1,3,2-dioxaphosphol-4-ene complex, and a P-alkoxyphosphane complex; the latter is formally derived from the enol form of the β-diketone. DFT calculations on the ring-expansion rearrangement support a preferred mechanism involving a pericyclic [1,3] shift of the phosphorus fragment in an oxaphosphirane complex rather than a stepwise diradical or ionic mechanism. The latter is slightly unfavored (ΔΔE‡ = 2.2 kcal/mol) and involves heterolytic P–C bond cleavage to give a methylene oxonium phosphanide intermediate and cyclization through a low-lying transition state featuring an unusual linear C–O–P geometry.
    Berichte der deutschen chemischen Gesellschaft 04/2014; 2014(10). · 2.94 Impact Factor
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    ABSTRACT: A hydrogen substituent at the 2-position directs the sulfonyl group to the N-3 position, while alkylsulfanyl or amino substituents lead to sulfonylation of the carbonyl oxygen.
    ChemInform 02/2014; 45(8).
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    ABSTRACT: Chromium–pyrenylcarbenes accessible from halopyrene precursors undergo benzannulation upon gentle warming with 3-hexyne to give hydroquinoid benzopyrene–Cr(CO)3 complexes. Kinetic benzannulation product 3 rearranges into thermodynamic haptotropomer 4 at 70 °C in octafluorotoluene under first-order kinetics. Further complexation of 3 by Cr(NH3)3(CO)3 affords syn and anti dinuclear chromium–benzopyrene complexes. Bidirectional extension of the benzannulation protocol results in the formation of syn and anti dibenzopyrene–dichromium complexes, which are structurally characterized by X-ray analysis.
    Berichte der deutschen chemischen Gesellschaft 02/2014; · 2.94 Impact Factor
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    ABSTRACT: SiO in a complex: The first silanone that is stable at room temperature (3) is reported. The two-step synthesis involves carbonylation of the silylidyne complex 1 to give the chromiosilylene 2, followed by oxidation of 2 with N2 O. Silanone 3 features a polar, short SiO bond (1.526(3) Å) to a trigonal-planar-coordinated silicon center and reacts with water to give the dihydroxysilyl complex.
    Angewandte Chemie International Edition 11/2013; · 13.73 Impact Factor
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    ABSTRACT: Synthesis of phosphinite complexes , and was achieved via reaction of transient Li/Cl phosphinidenoid complexes , prepared from dichloro(organo)phosphane complexes [(OC)5M{RPCl2}] (,: R = CPh3, ,: R = C5Me5, , : R = CH(SiMe3)2, , : M = W, : M = Mo, : M = Cr), with different alcohols (: R = allyl, : R = methyl, : R = isopropyl). Deprotonation of complexes , with MeLi or (t)BuLi in the presence of two equivalents of 12-crown-4 led to the selective formation of phosphinidenoid complexes [Li(12-crown-4)2] [(OC)5W{RP(OCH3)}] ( R = CPh3 and R = C5Me5) which were stable in solution at ambient temperature, in contrast to Li/OMe phosphinidenoid complexes without 12-crown-4. To our surprise attempts to crystallise complex yielded complex having a Li-O-P subunit. The reaction of complex with [Ph3C]BF4 yielded the P-C coupling product and, hence, the first evidence for an oxidative SET reaction. All isolated products were characterised by multinuclear NMR spectroscopy, IR, MS and single-crystal X-ray crystallography in the case of complexes , , , , and .
    Dalton Transactions 11/2013; · 3.81 Impact Factor
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    ABSTRACT: Four BINOL-based bis(4-pyridyl) ligands were synthesised in enantiopure and racemic form. These ligands form metallosupramolecular [(dppp)2M2L2] rhombi with cis-protected [(dppp)Pd]2+ and [(dppp)Pt]2+ ions. In principle, racemic ligands can self-assemble into three stereoisomeric rhombi. The degree of self-sorting in the self-assembly process crucially depends on the substitution pattern and the resulting bend angle of the V-shaped ligands as well as the degree of steric crowding within the assembly when racemic ligands are used. Thus, these processes either lead to homochiral assemblies in a narcissistic self-recognition manner, to heterochiral assemblies in a social self-discriminating manner, or proceed in a nonselective fashion as evidenced by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction.
    European Journal of Organic Chemistry 11/2013; 2014(1):206-216. · 3.34 Impact Factor
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    ABSTRACT: Bending the rules: Strained bicyclophanes with highly bent biphenylene units and a central aromatic moiety (yellow) forced into a perpendicular position were accessible in high yields by cyclization of the appropriate bromides by Yamamoto condensation. They were able to bind to graphite cutouts in solution and were adsorbed at the liquid/highly oriented pyrolytic graphite (HOPG) interface to form extended 2D structures.
    Angewandte Chemie International Edition 09/2013; · 13.73 Impact Factor
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    ABSTRACT: Azaphosphiridine complexes , intermediates in the reaction of P-C5Me5 substituted Li-Cl phosphinidenoid complex and C-furyl carbaldimine , rearranged selectively to give the novel N,P,C-cage complex . Transient terminal phosphinidene complex was trapped with phenyl acetylene () forming the new N,P,C-cage complex . DFT calculations provide evidence for a thermally allowed aza-phospha-Cope rearrangement that led to the P-amino substituted phosphinidene complex , which is stabilized by non-covalent interactions in addition to typical through-bond electronic effects.
    Chemical Communications 09/2013; · 6.38 Impact Factor
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    ABSTRACT: The sulfonylation of quinazolin-4(3H)-ones and related tetrahydrobenzothieno[2,3-d]pyrimidin-4-(3H)-ones with mesyl, tosyl, and para-cyanobenzenesulfonyl chloride was studied. A hydrogen substituent at 2-position directed the sulfonyl group to the N-3 position, while alkylsulfanyl or amino substituents led to sulfonylation of the carbonyl oxygen. The latter effect was attributed to steric influence and the positive mesomeric effect of the 2-substituent. An access to N-sulfonylated 2-substituted regioisomers was established. An unexpected 1,3-sulfonyl migration was observed and further analyzed. This process occurred as an intramolecular N- to O-shift as verified by kinetic and crossover experiments.
    The Journal of Organic Chemistry 08/2013; · 4.56 Impact Factor
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    ABSTRACT: Matter of opinion: The novel zwitterion 1 has been synthesized and studied theoretically and also converted into anionic NHCs 2. The former can also be described as a phosphinidene adduct of an abnormal N-heterocyclic carbene (1') and, in the same vein, the latter represents a phosphinidene adduct of an anionic N-heterocyclic dicarbene (2').
    Angewandte Chemie International Edition 08/2013; · 13.73 Impact Factor
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    ABSTRACT: A synthetic route to C(4/5)-bis(phosphinoyl)imidazole-2-thiones () (d: R(1) = (n)Bu, R(2) = Me; e: R(1) = n-dodecyl, R(2) = Me) and C(4/5)-bis(thio/selenophosphinoyl)imidazole-2-thiones (), () and (a: R(1) = R(2) = Me; b: R(1) = R(2) = Ph, c: R(1) = (i)Pr, R(2) = Me) is presented that employs initial C(5) lithiation of mono-phosphinoyl/thiophosphinoyl substituted imidazole-2-thiones ()/() followed by reaction with chlorodiphenylphosphane, leading to mixed phosphinoyl and phosphanyl substituted imidazole-2-thiones () or mixed thiophosphinoyl and phosphanyl substituted imidazole-2-thiones (). Subsequent oxidation of mixed phosphinoyl and phosphanyl substituted imidazole-2-thione () with H2O2-urea gives the bis(phosphinoyl) substituted imidazole-2-thiones (), and the oxidation of mixed thiophosphinoyl and phosphanyl substituted imidazole-2-thione () using H2O2-urea, elemental sulfur or elemental selenium gives a set of mixed P(v)-chalcogenide substituted imidazole-2-thiones (), () and , respectively. P(v,v) substituted imidazole-2-thiones and reacted with tellurium tetrachloride, titanium tetrachloride or palladium dichloride to give complexes , ( and ) and , respectively, having a bidentate chelate ( and ) or a monodentate bonding motif (). The titanium complexes slowly and selectively converted into the mono-ethoxy substituted product possessing a seven membered chelate motif being unprecedented in the titanium chemistry of phosphine oxide donor ligands. The compounds were characterized by elemental analyses, spectroscopic and spectrometric methods and, in addition, X-ray diffraction studies in the case of , , , and .
    Dalton Transactions 07/2013; · 3.81 Impact Factor
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    ABSTRACT: A new approach to the first complex featuring a manganese-tin triple bond is reported taking advantage of the propensity of dihydrogen complexes to eliminate H2. Reaction of the 18VE dihydrogen-hydride complex [MnH(ƞ2-H2)(dmpe)2] (1) (dmpe = Me2PCH2CH2PMe2) with the organotin(II) chloride SnCl(C6H3-2,6-Mes2) (Mes = 2,4,6-trimethylphenyl) afforded by H2-elimination selectively the chlorostannylidene complex trans-[H(dmpe)2Mn=Sn(Cl)-(C6H3-2,6-Mes2)] (2), which upon treatment with Na[B(C6H3-3,5-(CF3)2)4] or Li[Al(OC(CF3)3)4] was transformed quantitatively into the stannylidyne complex salts trans-[H(dmpe)2Mn≡Sn(C6H3-2,6-Mes2)]A (A = B(C6H3-3,5-(CF3)2)4; Al(OC(CF3)3)4) (3a/3b). The complexes 2 and 3a/3b were fully characterized, and the structures of 2 and 3a were determined by single-crystal X-ray diffraction. Complex 2 features the shortest Mn-Sn double bond reported so far, a large Mn-Sn-Caryl bond angle and a long Sn-Cl bond of the trigonal-planar coordinated tin center. These bonding features can be rationalised in valence-bond terms by a strong contribution of the triply-bonded resonance structure [LnMn≡SnR]Cl, and were verified by a NRT analysis of the electron density of the DFT-minimized structure of 2. Complex 3a features the shortest Mn-Sn bond reported so far, and a linear coordinated tin atom. NBO and NRT analyses of the electronic structure of the complex cation in 3a/3b suggest a highly polar Mn-Sn triple bond with a 65% ionic contribution to the NRT Mn-Sn bond order of 2.25. Complex 3a undergoes a reversible one-electron reduction suggesting that open-shell stannylidyne complexes might be accessible using strong reducing agents.
    Journal of the American Chemical Society 07/2013; · 10.68 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: A 1,1'-binaphthyl-based bis(pyridine) ligand (1) was prepared in racemic and enantiomerically pure form to study the formation of [Pd2 (1)4 ] complexes upon coordination to palladium(II) ions with regard to the degree of chiral self-sorting. The self-assembly process proceeds in a highly selective narcissistic self-recognition manner to give only homochiral supramolecular M2 L4 cages, which were characterized by ESI-MS, NMR, and electronic circular dichroism (ECD) spectroscopy, as well as by single-crystal XRD analysis.
    Chemistry 07/2013; 9(33):10890-10894. · 5.93 Impact Factor
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    ABSTRACT: Ligand swap: The exchange of N-heterocyclic carbene (NHC) ligands at Si(II) centers is shown to provide access to a dicationic NHC complex of silicon(II), and an NHC adduct of the iodosilyliumylidene cation SiI(+) , [SiI(IiPr2 Me2 )(IDipp)](+) . Characterization studies led to the discovery of an unprecedented CH⋅⋅⋅Si anagostic interaction for [SiI(IiPr2 Me2 )(IDipp)](+) .
    Angewandte Chemie International Edition 05/2013; · 13.73 Impact Factor
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    ABSTRACT: In situ formed Li/Cl phosphinidenoid complexes [Li(12-crown-4)][M(CO)5(ClPC5Me5)] (M = Cr, Mo, W) reacted with cyclobutanone (), cyclopentanone () and cyclohexanone () in Et2O to yield the first P-C5Me5 substituted C(3)-spirofused oxaphosphirane complexes , and . In the case of cyclopentanone and the outcome of the reaction in THF was different: here the formation of along with (anionic) phosphinoate complexes and was observed, the latter possess an unusual ring-opened oxaphosphirane and 2-cyclopentylidenecyclopentanone as co-ligands to the lithium cation. NMR, IR and MS data as well as single-crystal X-ray structures in the case of , , and are reported. DFT calculations on the parent 1-oxa-2-phosphaspiro[2.n]alkane pentacarbonylchromium(0) complexes (: n = 2; : n = 3; : n = 4; : n = 5) revealed that both ring strain energies and G(r) values decrease significantly as the spiroring size increases. This is caused by an increase in the exocyclic α bond angle at the oxaphosphirane C(3) atom, hence decreasing the s-character of the corresponding orbitals involved in endocyclic bonds at C(3) and thus becoming better suited for accommodation of small ring angles.
    Dalton Transactions 05/2013; · 3.81 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: The synthesis of P-F phosphane metal complexes [(CO)5M{RP(H)F}] 2a-c (R = CH(SiMe3)2; a: M = W; b: M = Mo; c: M = Cr) is described using AgBF4 for a Cl/F exchange in P-Cl precursor complexes [(CO)5M{RP(H)Cl}] 3a-c; thermal reaction of 2H-azaphosphirene metal complexes [(CO)5M{RP(C(Ph)═N}] 1a-c with [Et3NH]X led to complexes 3a-c, 4, and 5 (M = W; a-c: X = Cl; 4: X = Br; 5: X = I). Complexes 2a-c, 3a-c, 4, and 5 were deprotonated using lithium diisopropylamide in the presence of 12-crown-4 thus yielding Li/X phosphinidenoid metal complexes [Li(12-crown-4)(Et2O)n][(CO)5M(RPX)] 6a-c, 7a-c, 8, and 9 (6a-c: M = W, Mo, Cr; X = F; 7a-c: M = W, Mo, Cr; X = Cl; 8: M = W; X = Br; 9: M = W; X = I). This first comprehensive study on the synthesis of the title compounds reveals metal and halogen dependencies of NMR parameters as well as thermal stabilities of 6a, 7a, 8, and 9 in solution (F > Cl > Br > I). DOSY NMR experiments on the Li/F phosphinidenoid metal complexes (6a-c; M = W, Mo, Cr) rule out that the cation and anion fragments are part of a persistent molecular complex or tight ion pair (in solution). The X-ray structure of 6a reveals a salt-like structure of [Li(12-crown-4)Et2O][(CO)5W{P(CH(SiMe3)2)F}] with long P-F and P-W bond distances compared to 2a. Density functional theory (DFT) calculations provide additional insight into structures and energetics of cation-free halophosphanido chromium and tungsten complexes and four contact ion pairs of Li/X phosphinidenoid model complexes [Li(12-crown-4)][(CO)5M{P(R)X}] (A-D) that represent principal coordination modes. The significant increase of the compliance constant of the P-F bond in the anionic complex [(CO)5W{P(Me)F}] (10a) revealed that a formal lone pair at phosphorus weakens the P-F bond. This effect is further enhanced by coordination of lithium and/or the Li(12-crown-4) countercation (to 10a) as in type A-D complexes. DFT calculated phosphorus NMR chemical shifts allow for a consistent interpretation of NMR properties and provide a preliminary explanation for the "abnormal" NMR shift of P-Cl derivatives 7a-c. Furthermore, calculated compliance constants reveal the degree of P-F bond weakening in Li/F phosphinidenoid complexes, and it was found that a more negative phosphorus-fluorine coupling constant is associated with a larger relaxed force constant.
    Inorganic Chemistry 03/2013; · 4.59 Impact Factor
  • Alexander C Filippou, Uttam Chakraborty, Gregor Schnakenburg
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    ABSTRACT: A general approach to the first compounds that contain rhenium-germanium triple and double bonds is reported. Heating [ReCl(PMe3 )5 ] (1) with the arylgermanium(II) chloride GeCl(C6 H3 -2,6-Trip2 ) (2; Trip=2,4,6-triisopropylphenyl) results in the germylidyne complex mer-[Cl2 (PMe3 )3 ReGeC6 H3 -2,6-Trip2 ] (4) upon PMe3 elimination. An equilibrium that is dependent on the PMe3 concentration exists between complexes 1 and 4. Removal of the volatile PMe3 shifts the equilibrium towards complex 4, whereas treatment of 4 with an excess of PMe3 gives a 1:1 mixture of 1 and the PMe3 adduct of 2, GeCl(C6 H3 -2,6-Trip2 )(PMe3 ) (2-PMe3 ). Adduct 2-PMe3 can be selectively obtained by addition of PMe3 to chlorogermylidene 2. The NMR spectroscopic data for 2-PMe3 indicate an equilibrium between 2-PMe3 and its dissociation products, 2 and PMe3 , which is shifted far towards the adduct site at ambient temperature. NMR spectroscopic monitoring of the reaction of complex 1 with 2 and the reaction of complex 4 with PMe3 revealed the formation of two key intermediates, which were identified to be the chlorogermylidene complexes cis/trans-[Cl(PMe3 )4 ReGe(Cl)C6 H3 -2,6-Trip2 ] (cis/trans-3) by using NMR spectroscopy. Labile chlorogermylidene complexes cis/trans-3 can be also generated from trans-[Cl(PMe3 )4 ReGeC6 H3 -2,6-Trip2 ]BPh4 (9) and (nBu4 N)Cl at low temperature, and decompose at ambient temperature to give a mixture of complexes 1 and 4. Complex 4 reacts with LiI to give the diiodido derivative mer-[I2 (PMe3 )3 ReGeC6 H3 -2,6-Trip2 ] (5), which undergoes a metathetical iodide/hydride exchange with Na(BEt3 H) to give the dihydrido germylidyne complex mer-[H2 (PMe3 )3 ReGeC6 H3 -2,6-Trip2 ] (6). Carbonylation of 4 induces a chloride migration from rhenium to the germanium atom to afford the chlorogermylidene complex mer-[Cl(CO)(PMe3 )3 ReGe(Cl)C6 H3 -2,6-Trip2 ] (7). Similarly, MeNC converts complex 4 into the methylisocyanide analogue mer-[Cl(MeNC)(PMe3 )3 ReGe(Cl)C6 H3 -2,6-Trip2 ] (8). Chloride abstraction from 4 by NaBPh4 in the presence of PMe3 gives the cationic germylidyne complex trans-[Cl(PMe3 )4 ReGeC6 H3 -2,6-Trip2 ]BPh4 (9). Heating complex 4 with cis-[Mo(PMe3 )4 (N2 )2 ] induces a germylidyne ligand transfer from rhenium to molybdenum to afford the germylidyne complex trans-[Cl(PMe3 )4 MoGeC6 H3 -2,6-Trip2 ] (10). All new compounds were fully characterized and their molecular structures studied by X-ray crystallography, which led to the first experimentally determined ReGe triple- and double-bond lengths.
    Chemistry 02/2013; · 5.93 Impact Factor
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    ABSTRACT: Three new aromatic acids, named lahorenoic acids A (1), B (2), and C (3), have been isolated along with the known compounds phenazine-1-carboxylic acid (4), 2-hydroxyphenazine-1-carboxylic acid (5), 2-hydroxyphenazine (6), 2,8-dihydroxyphenazine (7), cyclo-Pro-Tyr (8), cyclo-Pro-Val (9), cyclo-Pro-Met (10), and WLIP (11) and characterized from the biocontrol strain Pseudomonas aurantiaca PB-St2. The structures of these compounds were deduced by 1D and 2D NMR spectroscopic and mass spectral data interpretation. Compounds 2, 4, and 7 showed moderate antibacterial activity against mycobacteria and other Gram-positive bacteria, while 4 was also found to exhibit cytotoxic and antifungal properties.
    Journal of Natural Products 02/2013; 76(2):135-41. · 3.29 Impact Factor
  • Journal of Polymer Science A Polymer Chemistry. 02/2013; 51(4):987-992.

Publication Stats

174 Citations
359 Downloads
634.47 Total Impact Points

Institutions

  • 2006–2014
    • University of Bonn
      • • Institute for Inorganic Chemistry
      • • Pharmazeutisches Institut
      • • Kekulé Institute of Organic Chemistry and Biochemistry
      Bonn, North Rhine-Westphalia, Germany
  • 2010–2012
    • Johannes Gutenberg-Universität Mainz
      • Institute of Organic Chemistry
      Mainz, Rhineland-Palatinate, Germany
  • 2002–2004
    • Humboldt-Universität zu Berlin
      • Department of Chemistry
      Berlin, Land Berlin, Germany