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Gierz V.,University of Tübingen | Seyboldt A.,University of Tübingen | Maichle-Mossmer C.,University of Tübingen | Frohlich R.,Organisch Chemisches Institute | And 2 more authors.
European Journal of Inorganic Chemistry | Year: 2012

A straightforward synthesis method for mixed phosphane dipyrido-annelated N-heterocyclic carbene (dipiy) palladium(II) complexes is presented. The key step is the oxidative addition of 6-bromodipyridoimidazolium bromides that can be prepared easily from dipyridine in a two step reaction. This new procedure avoids any generation of the free carbene as well as any transmetallation step. The straightforward synthesis of mixed dipyrido NHC-phosphane Pd II complexes by the oxidative addition of 6-bromodipyridoimidazolium salts is presented. This procedure avoids any transmetallation step orformation of a free carbene. Synthesis of the brominated starting material can easily be achieved by reaction of the corresponding imidazolium or benzoylimidazolium salt with bromine. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zeng Z.,Institute For Physikalische Chemie | Matuschek D.,Organisch Chemisches Institute | Studer A.,Organisch Chemisches Institute | Schwickert C.,Institute For Anorganische Und Analytische Chemie | And 2 more authors.
Dalton Transactions | Year: 2013

Hybrid materials, in which stable organic radical cations are intercalated into layered inorganic host materials, can be successfully synthesized via an ion exchange reaction in a layered fluoromica clay, to yield recyclable heterogeneous catalysts for oxidation of various alcohols. We have conducted systematic synthetic and structural studies on the intercalation of the radical cations 4-(diethylmethylammonium)-2,2,6,6-tetramethylpiperidin-1-oxyl (DEMTEP), 1-[2-(4-amino-2,2,6,6-tetramethyl-1-piperidinyloxyl)-2-oxoethyl] -1′-methyl-4,4′-bipyridinium (VIOTEP), and 2-(3-N-methylpyridinium)- 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-N-oxide (m-MPYNN) into a synthetic fluoromica clay named Somasif® ME 100, Na2xMg 3.0-xSi4O10(FyOH1-y) 2 (x = 0.33, y = 0.98). The guest-host interactions in these intercalation compounds have been characterized by X-ray powder diffraction and solid-state NMR of the constituent nuclei (23Na, 19F, and 29Si) of the Somasif structure. The intercalation process can be conveniently monitored using 23Na MAS-NMR. Guest-guest interactions have been probed by magnetic susceptibility measurements as well as EPR and 1H MAS NMR experiments. The 1H MAS-NMR line widths and chemical shifts probe modifications in the electron spin density distributions and/or intermolecular interactions between the electron spins of the guest species. Despite these indications of weakly interacting spins, magnetic susceptibility measurements are consistent with the near-absence of cooperative magnetism. The VIOTEP and DEMTEP inclusion compounds demonstrate catalytic activity for the oxidation of benzyl alcohol, using NaOCl as a co-oxidant. Although the radical ion species is partially leached out under these conditions (ionic exchange with Na+ in solution) the catalytic activity remains for up to 40 subsequent cycles. Fully leached materials can be regenerated by catalyst re-loading and this process can be conveniently monitored by X-band EPR spectroscopy. © 2013 The Royal Society of Chemistry.

Wiegand T.,Institute For Physikalische Chemie | Eckert H.,Institute For Physikalische Chemie | Ekkert O.,Organisch Chemisches Institute | Frohlich R.,Organisch Chemisches Institute | And 3 more authors.
Journal of the American Chemical Society | Year: 2012

Covalent bonding interactions between the Lewis acid and Lewis base functionalities have been probed in a series of "frustrated Lewis pairs" (FLPs) (mainly substituted vinylene linked intramolecular phosphane-borane adducts), using solid-state nuclear magnetic resonance techniques and accompanying DFT calculations. Both the 11B NMR isotropic chemical shifts and nuclear electric quadrupolar coupling parameters turn out to be extremely sensitive experimental probes for such interactions, revealing linear correlations with boron-phosphorus internuclear distances. The principal component V zz of the 11B electric field gradient tensor is tilted slightly away (∼20°) from the boron-phosphorus internuclear vector, leading to an improved understanding of the remarkable reactivity of the FLPs. Complementary 31P{ 1H}-CPMAS experiments reveal significant 31P- 11B scalar spin-spin interactions ( 1J ∼ 50 Hz), evidencing covalent bonding interactions between the reaction centers. Finally, 11B{ 31P} rotational echo double resonance (REDOR) experiments show systematic deviations from calculated curves based on the internuclear distances from X-ray crystallography. These deviations suggest non-zero contributions from anisotropic indirect spin-spin (J anisotropy) interactions, thereby offering additional evidence for covalent bonding. © 2012 American Chemical Society.

Piel I.,Organisch Chemisches Institute | Dickschat J.V.,University of Munster | Pape T.,University of Munster | Hahn F.E.,University of Munster | Glorius F.,Organisch Chemisches Institute
Dalton Transactions | Year: 2012

The reaction of pseudo-ortho-4,12-N,N′-diphenyldiamino-[2.2] paracyclophane ((±)-3) with Sn[N(SiMe3)2] 2 results in the formation of the monomeric planar chiral N-heterocyclic stannylene (±)-4, featuring a unique [2.2]paracyclophane backbone, which has been characterized by an X-ray diffraction study. © 2012 The Royal Society of Chemistry.

Stute A.,Organisch Chemisches Institute | Kehr G.,Organisch Chemisches Institute | Daniliuc C.G.,Organisch Chemisches Institute | Frohlich R.,Organisch Chemisches Institute | Erker G.,Organisch Chemisches Institute
Dalton Transactions | Year: 2013

2-Propenylbis(pentafluorophenyl)phosphane adds Piers' borane [HB(C 6F5)2] with anti-Markovnikov orientation to yield the intramolecular vicinal frustrated P/B Lewis pair 10. The FLP 10 adds pyridine, acetonitrile or alkyl isocyanides to form simple boron Lewis acid adducts 11-14, all of which were characterized by X-ray diffraction. The FLP 10 reacts with trans-cinnamic aldehyde to give a boron carbonyl adduct 15 that was characterized by an X-ray crystal structure analysis. In contrast, the geminal FLP (C6F5)2P-CHEt-B(C6F 5)2 (3) undergoes 1,2-carbonyl addition reactions with benzaldehyde or trans-cinnamic aldehyde to yield the respective five-membered heterocyclic products (7, 8, both characterized by X-ray diffraction). The FLP 10 undergoes 1,2-P/B addition to p-tolylacetylene and to 2-methylbutenyne, respectively, to yield the corresponding six-membered heterocyclic products 17 and 18, respectively (both were characterized by X-ray diffraction). © The Royal Society of Chemistry 2013.

Shi Z.,Organisch Chemisches Institute | Glorius F.,Organisch Chemisches Institute
Angewandte Chemie - International Edition | Year: 2012

Complement for Fischer: An efficient palladium-catalyzed indole synthesis proceeds by the intramolecular cross-dehydrogenative coupling of N-aryl imines under mild conditions using molecular oxygen as the sole oxidant. This practical method relies on anilines and ketones as starting materials (and thus the same retrosynthetic disconnection as the Fischer indole synthesis) and will likely become a popular route. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stauch T.,The Interdisciplinary Center | Scholtes J.F.,Organisch Chemisches Institute | Dreuw A.,The Interdisciplinary Center
Chemical Physics Letters | Year: 2016

The inverse electron-demand Diels-Alder reaction of trans-cyclooctene and sym-tetrazine is a bioorthogonal reaction which has found widespread applications during the last decade, e.g. for fluorescent labeling of living cells. However, the use of this reaction is still limited due to the rapid isomerization of trans-cyclooctene to its unreactive cis-conformer. Using computational methods, we have derived two optimized derivatives of trans-cyclooctene, which pave the road to more efficient in vivo labeling of arbitrary proteins. © 2016 Elsevier B.V. All rights reserved.

Koroniak K.,Organisch Chemisches Institute | Haufe G.,Organisch Chemisches Institute
Synthesis | Year: 2010

A series of diastereomeric fluorinated and nonfluorinated triazolo analogues of naturally occurring sphingolipids like dihydroceramide suitable for physicochemical and medicinal chemistry applications were prepared enantioselectively. Key steps of the synthetic sequence are asymmetric Sharpless dihydroxylation of α,β-unsaturated esters to diols, regioselective ring opening of derived cyclic sulfates by azide, 1,3-dipolar cycloaddition with alkynes, and reduction of the ester groups. © Georg Thieme Verlag Stuttgart New York.

Koroniak K.,Organisch Chemisches Institute | Haufe G.,Organisch Chemisches Institute
Synthesis | Year: 2010

The synthesis of a series of different fluorinated analogues of sphinganine and dihydroceramide using Staudinger ligation of diastereomeric 2-azido-4-fluoro-3-hydroxyoctadecanoates and subsequent selective ester reduction as key steps is presented. The formed sphingolipid analogues are interesting for medicinal studies as well as for the investigation of their phase behavior at interfaces. © 2010 Georg Thieme Verlag Stuttgart New York.

Albrecht M.,RWTH Aachen | Isaak E.,RWTH Aachen | Baumert M.,RWTH Aachen | Gossen V.,RWTH Aachen | And 2 more authors.
Angewandte Chemie - International Edition | Year: 2011

Undecided! A titanium(IV) triscatecholate bearing chiral ester groups shows different CD spectra in methanol and DMSO. The observation of different stereoisomers lies in the preferred conformation of the side groups in the monomer and dimer, which leads to different chiral induction in the different species. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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