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Organische Chemie
Prof. Dr. Jan Paradies
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Peer Revied Publications

[53] "Borane catalyzed redox isomerization of 2-amino chalcones: hydride abstraction or hydride migration" Rundong Zhou, Jan Paradies Eur. J. Org. Chem. 2021, accepted, DOI:10.1002/ejoc.202100883

The borane catalyzed redox isomerization of 2-amino chalcones is developed. The tetrahydroquinolines are obtained in high yield as a mixture of cis/trans diastereomers in a ratio of 2:1 to >95:5. The reaction mechanism is investigated by mechanistic, kinetic and computational methods, concluding that the reaction proceeds through concerted [1,5] hydride shift in contrast to borane-mediated C(sp3)–H hydride abstraction.

[52] "Mixed-valence compounds as polarizing agents for Overhauser dynamic nuclear polarization in solids" Andrei Gurinov, Benedikt Sieland, Andrei Kuzhelev, Hossam Elgabarty, Thomas D. Kühne, Thomas Prisner, Jan Paradies, Marc Baldus, Konstantin L. Ivanov and Svetlana Pylaeva∗ Angew. Chem. Int. Ed. 2021, 60, 15371 –15375, .DOI:10.1002/anie.202103215 and 10.1002/ange.202103215.

In this paper we investigate a novel set of polarizing agents ‐ mixed‐valence compounds ‐ by theoretical and experimental methods and demonstrate their performance in high‐field Dynamic Nuclear Polarization (DNP) NMR experiments in the solid state. Mixed‐valence compounds constitute a group of molecules, in which molecular mobility persists even in solids. Consequently, such polarizing agents can be used to perform Overhauser‐DNP experiments in solid‐state, with favorable conditions for dynamic nuclear polarization formation at ultra‐high magnetic fields.

[51] "Diastereoselective Synthesis of Dihydro-quinolin-4-ones by a Borane-Catalyzed Redox-Neutral endo-1,7-Hydride Shift" Garrit Wicker, Roland Schoch, Jan Paradies Org. Lett. 2021, 23 3626–3630. DOI:10.1021/acs.orglett.1c01018.

The borane-catalyzed synthesis of dihydroquinoline-4-ones is developed. The amino-substituted chalcones undergo a 1,7-hydride shift upon Lewis acid activation to form a zwitterionic iminium enolate, which collapses to the dihydroquinoline-4-one scaffold. The reaction proceeds in high yields (75–99%) with an excellent diastereoselectivity of up to >99:1 (cis:trans). The reaction mechanism is investigated by kinetic, isotope labeling, and computational experiments.

[50] "Hydrogenation of secondary amides using phosphane oxide and frustrated Lewis pair catalysis" Laura Köring, Nikolai A. Sitte, Markus Bursch, Stefan Grimme, Jan Paradies Chem. Eur. J. 2021, accepted. DOI:10.1002/chem.202100041.

The metal‐free catalytic hydrogenation of secondary carboxylic acid amides is developed. The reduction is realized by two new catalytic reactions. First, the amide is converted into the imidoyl chloride by triphosgene (CO(OCCl3)2) using novel phosphorus(V) catalysts. Second, the in situ generated imidoyl chlorides are hydrogenated in high yields by an FLP‐catalyst. Mechanistic and quantum mechanical calculations support an autoinduced catalytic cycle for the hydrogenation with chloride acting as unusual Lewis base for FLP‐mediated H2‐activation.

[49] "FLP-catalysis meets hydrogen-bond activation" Nikolai A. Sitte, Laura Köring, Peter W. Roesky, Jan Paradies Org. Biomol. Chem. 2020, 18, 7321-7325. DOI:10.1039/D0OB01492C.

The potential of two chiral amidines and three non-chiral boranes in the metal-free hydrogen activation was explored. The resulting chiral amidiunium borohydride salts were investigated in asymmetric hydrogenation reactions of ketimines, activated double bonds and dehydro amioacid esters.

[48] "Dually Cross-linked Supramolecular Hydrogel for Cancer Biomarker Sensing" Li, Jie; Ji, Chendong; Lü, Baozhong; Rodin, Maksim; Paradies, Jan; Yin, Meizhen;* Kuckling, Dirk ACS Appl. Mat. Int. 2020, 33, 36873–36881. DOI:a10.1021/acsami.0c08722.

Lysophosphatidic acid (LPA) as the biomarker of early stage ovarian cancer is essentially difficult to be detected due to lack of target spots. A dually crosslinked supramolecular hydrogel (DCSH) was developed to achieve sensing of LPA, which act as a competitive guest molecule triggering the responsive crosslinking of the DCSH. Through this strategy, the surface plasmon resonance combined with optical waveguide spectroscopy could be used to quantitatively detect LPA with a responsive range covering physiological conditions (in pure form as well as mimicking LPA plasma solution) with high selectivity and sensitivity. LPA efficiently insert into the host molecule β-cyclodextrin (β-CD) up to a 1:2 ratio as the competitive interaction mechanism confirmed by onedimensional nuclear overhauser effect spectroscopy (1D NOESY), high resolution mass spectrometry (HRMS), isothermal titration calorimetry (ITC) and computational simulation. Our method opens a new strategy to detect biomarkers without target spot and provides a platform for surface plasmon resonance (SPR) based sensors measuring small molecules.

[47] "Palladium-Catalyzed Polycondensation for the Synthesis of Poly(Aryl)Sulfides" Peng Hou, Peter Oechsle, Dirk Kuckling, and Jan Paradies* Macromol. Rapid Commun. 2020, 41, 2000067. DOI:10.1002/marc.202000067.

The palladium catalyzed C–S cross coupling reaction is investigated as novel efficient tool for the synthesis of poly(phenyl)sulfide derivatives. The reaction proceeds through the polycondensation of dibromo arenes with a H2S surrogate to yield poly(aryl)sulfides. The reaction is generalized by the synthesis of so far unprecedented poly(2,5-thiophene)sulfide. Number average molecular weights of up to 3780 and 1770 g mol−1 for poly(phenyl)sulfide and poly(thiophene)sulfide are achieved with degrees of polymerization (DPn) of 10 and 7, respectively. A mechanism for the new polycondensation reaction is suggested.

[46] "Redox-responsive phosphonite gold complexes in hydroamination catalysis" Eva Deck, Hanna E. Wagner, Jan Paradies* and Frank Breher* Chem. Commun. 2019, 55, 5323-5326. DOI:10.1039/c9cc01492f.

Very high activities were observed in the redox-induced hydroamination of alkynes by employing a redox-active gold(I) complex featuring an electron-deficient, terphenyl-substituted phosphonitebased ligand. The hydroamination proceeds roughly two-fold faster with the in situ oxidized catalysts than with their reduced form.

[45] "From structure to novel reactivity in frustrated Lewis pairs" J. Paradies Coord. Chem. Rev. 2019, 380, 170-183. DOI:10.1016/j.ccr.2018.09.014.

The coexistence of a strong Lewis acid and a Lewis base in solution, the so called frustrated Lewis pair, has led to the discovery of metal-free hydrogen activation. Since then, this observation has inspired numerous chemists to develop more examples. Metal-free hydrogenation is so far the most studied application of frustrated Lewis pairs in chemistry and highly efficient methodologies for a number of substrates have been developed. However, the targeted choice of a FLP-catalyst is yet rather intricate, due to the lack of an in depth understanding of FLP-reactivity. The presented structure-reactivity-relationship for hydrogenation reactions allowed the targeted development and optimization of unprecedented reactions using FLPs as catalysts. This article provides insight into FLP-reactivity by summarizing our mechanistic and synthetic work in this field.

[44] "Frustrated Lewis Pair Catalyzed Hydrogenation of Amides: Halides as Active Lewis Base in the Metal-Free Hydrogen Activation" N. Sitte, M. Bursch, S. Grimme,* J. Paradies* J. Am. Chem. Soc. 2019, 141, 159-162. DOI:10.1021/jacs.8b12997.

A method for the metal-free reduction of carboxylic amides using oxalyl chloride as activating agent and hydrogen as final reductant is introduced. The reaction proceeds via the hydrogen splitting by B(2,6-F2-C6H3)3 in combination with chloride as the Lewis base. Density functional theory calculations support the unprecedented role of halides as active Lewis base components in the frustrated Lewis pair mediated hydrogen activation. The reaction displays broad substrate scope for tertiary benzoic acid amides and alpha-branched carboxamides.

[43] "Borane-catalyzed synthesis of quinolines bearing tetrasubstituted stereocenters by hydride abstraction-induced electrocyclization" A. F. G. Maier, S. Tussing, H. Zhu, G. Wicker, P. Tzvetkova, U. Flörke, C. G. Daniliuc, S. Grimme,* Jan Paradies* Chem. Eur. J. 2018, 24, 16287. DOI:10.1002/chem.201804777.

The borane-catalyzed synthesis of quinoline derivatives bearing tetrasubstituted stereocenters from vinyl anilines has been developed. Mechanistic studies and quantum-mechanical investi¬gations support the hydride abstraction/electro¬cycli¬zation/hydride addition mechanism. The products were obtained in up to 99% yield with a diastereoselectivity of >99% in favour for the 3a-5-cis isomer.

[42] Electrophilic phosphonium cation-mediated phosphane oxide reduction using oxalyl chloride and hydrogen A. J. Stepen, M. Bursch, S. Grimme,* D. W. Stephan,* J. Paradies* Angew. Chem. 2018, 130, 15473–15476; Angew. Chem. Int. Ed. 2018, 57,15253–15256. DOI:10.1002/anie.201809275 and 10.1002/ange.201809275.

The metal-free reduction of phosphane oxides with molecular hydrogen (H2) using oxalyl chloride as activating agent was achieved. Quantum-mechanical investigations support the heterolytic splitting of H2 by the in situ formed electrophilic phosphonium cation (EPC) and phosphane oxide and subsequent barrierless conversion to the phosphane and HCl. The reaction can also be catalyzed by the frustrated Lewis pair (FLP) consisting of B(2,6-F2C6H3)3 and 2,6-lutidine or phosphane oxide as Lewis base. This novel reduction was demonstrated for triaryl and diaryl phosphane oxides providing access to phosphanes in good to excellent yields (51-93%).

[41] "Mechanisms in FLP-catalyzed reactions" J. Paradies Eur. J. of Org. Chem. 2019, 283–294. DOI:10.1002/ejoc.201800944.

This review summarizes the principle reaction mechanisms of frustrated Lewis pairs (FLP) in hydrogenations and carbon-nitrogen and carbon-carbon bond forming reactions. The fundamental mechanism of hydrogen activation by FLPs is reviewed and the influence of the FLP’s nature on hydrogenation reactions is discussed, leading to a structure-reactivity relationship in phosphine/borane or amine/borane derived FLPs. This reactivity concept is validated for a series of FLP-catalyzed reactions. Furthermore, alternative reaction mechanisms e.g. protodeborations or sigma-bond metathesis are discussed.

[40] "Liquid Crystalline Dithienothiophene Derivatives for Organic Electronics" J. Vollbrecht, A. Stepen, F. Hoffmann, P. Oechsle, J. Paradies, T. Meyers, U. Hilleringmann, J. Schmidtke, H. Kitzerow* Org. Electronics 2018,61, 266-275. DOI:10.1016/j.orgel.2018.06.002.

The synthesis and mesophase characterization of two 2,6-bis(4-(alkyloxy)phenyl)dithieno [3,2-b:2′,2′-d]thiophenes indicate successful application of a palladium-catalyzed carbon-sulfur cross-coupling/5-endo-dig cyclization sequence and the appearance of a nematic mesophase in the resulting products. Spectroscopic and cyclovoltammetric measurements reveal molecular orbital energies that are comparable to a good standard hole conductor. Consequently, one of the compounds was successfully applied as a hole conducting layer in an electroluminescent sample. In thin-film transistors (TFT), the two compounds show charge carrier mobilities in the saturation region μsat of 0.13 cm2V−1s−1 and 0.03 cm2V−1s−1, respectively. The injection barrier at the metal semiconductor interface could be reduced by alkanethiol treatment, thereby enabling a linear ID (VD) characteristics in the low VD region and maximum currents up to ID,max = - 18 μA at VG = - 2.5 V in the saturation regime. Inverter circuits in single-type TFT technology were implemented.

[39] "Perfluoroalkylated Main-Group Element Lewis Acids as Catalysts in Transfer Hydrogenation" J. Bader, A. F. G. Maier, J. Paradies, B.Hoge* Eur. J. of Inorg. Chem. 2017, 24, 3053–3056. DOI:10.1002/ejic.201700524.

Transfer hydrogenation plays an important part in organic chemistry. Recently, strong Lewis acids like B(C6F5)3 have been introduced as a catalyst for these reactions. We successfully employed the Lewis acid (C2F5)3PF2 as a catalyst in the transfer hydrogenation between 1,3,5‐trimethylcyclohexa‐1,4‐diene and 1,1‐diphenylethylene. Surprisingly, the treatment of the diene alone with a catalytic amount of (C2F5)3PF2 led to a quantitative dismutation to mesitylene and 1,3,5‐trimethylcyclohexane. With B(C6F5)3, there was a solvent‐dependency: in CH2Cl2 mainly the dismutation products were obtained, while in toluene the evolution of H2 was observed. Additionally, the catalytic activity of various perfluoroalkylated germanes and silanes was tested.

[38] "Double-Strand DNA Breaks Induced by Paracyclophane Gold(I) Complexes" S. Bestgen, C. Seidl, T. Wiesner, A. Zimmer, M. Falk, B. Köberle, M. Austeri, J. Paradies, S. Bräse, U. Schepers,* P. W. Roesky* Chem. Eur. J. 2017, 23, 6315–6322.

Gold(I) complexes of ClickPhos [2.2]paracyclophane ligands were synthesized in excellent yields and fully characterized by spectroscopic methods as well as X‐ray crystallography. The complexes exhibit a rigid ligand backbone and a triazolyl moiety and were systematically studied with respect to their cytotoxic properties. In combination with the ionic complex [(GemPhos)Au(tht)][ClO4] (tht=tetrahydrothiophene), in which the gold(I) atom exhibits a distorted trigonal coordination sphere of two phosphines and a labile tht ligand, their efficiency in cytotoxicity was investigated in HeLa, MCF7, and HCT116 cells as well as in a zebrafish model. Their cytotoxicity and their mechanisms of action are different and involve apoptosis, necrosis, and DNA damage. The compounds presented herein are potent metal‐based cytostatics displaying LD50 values from 3.5–38 μm in different tumor cell lines and induce double‐strand DNA breaks (DSB) as shown by H2AX phosphorylation (γH2AX) at foci of DSBs.

[37] "Borane-catalyzed indole synthesis through intramolecular hydroamination" S. Tussing, M. Ohland, G. Wicker, U. Flörke, J. Paradies* Dalton Trans. 2017, 46, 1539-1545.
The reaction of 2-alkynyl anilines with catalytic amounts of B(C6F5)3 (5 mol%) resulted in the formation of 2-substituted indoles according to an intramolecular hydroamination in good to excellent yields. Reaction intermediates as well as products were characterized by NMR spectroscopy and by X-ray crystallography. The domino hydroamination/hydrogenation sequence allowed the efficient synthesis of tetrahydroquinoline in good yield.

[36] "Heteroacene synthesis through C–S cross coupling / 5-endo-dig cyclization" Peter Oechsle, Ulrich Flörke, Hans Egold, and Jan Paradies Chem. Eur. J. 2016, 51, 18559-18563.
The highly efficient, one step of sulfur-containing heteroacenes was achieved through palladium-catalyzed C–S cross coupling of bisalkynes with thioacetate as hydrogen sulfide surrogate. The heteroacenes consisting of three, five and seven fused aromatic rings were obtained in one single catalytic step by four-, six- and eight-fold C–S bond formation.

[35] “Concise synthesis of dithiophene derivatives by palladium-catalyzed multiple C–S cross coupling/cyclization sequence” Peter Oechsle,a Peng Hou,a Ulrich Flörkeb and Jan Paradiesa*, Adv. Synth Catal. 2016, 7, 3770-3776, DOI:10.1002/adsc.201600802
The facile synthesis of new sulfur-containing fused heterocycles was achieved by a twofold domino reaction consisting of a carbon-sulfur cross coupling, followed by a 5-endo-dig cyclization. Using this strategy a series of benzo, thiopheno, pyridino and pyrazino dithienoacenes with electron-neutral (-C6H4-nHex), electron-rich (-C6H4-NPh2) and electron-deficient (-C4H3N2) substituents were synthesized in high yields. The developed method was applied in the efficient synthesis of a complex donor-acceptor molecule. The photophysical and electrochemical properties of the products were analyzed by UV-VIS/luminescence spectroscopy and cyclic voltammetry.

[34]  "Frustrated Lewis Pair-catalyzed dehydrogenative oxidation of indolines and other heterocycles"  Alexander F. G. Maier, Sebastian Tussing, Tobias Schneider, Ulrich Flörke, Zheng-Wang Qu, Stefan Grimme* and Jan Paradies* Angew. Chem. 2016, 55, 12219–12223The FLP-catalyzed acceptorless dehydrogenation of heterocycles was developed. The oxidation with concomitant liberation of molecular hydrogen proceeded in high to excellent yields for N-protected indolines as well as four other substrate classes. The mechanism of this unprecedented FLP-catalyzed reaction was investigated by mechanistic studies, characterization of reaction intermediates by NMR spectroscopy and x-ray crystal analysis and by quantum-mechanical calculations. The hydrogen liberation from the intermediary formed ammonium hydroborate is the rate deter­mining step of the oxidation. The addition of a weaker Lewis-acid as hydride shuttle increased the reaction rate by 2.28 though a second catalytic cycle.

[33] "Structure-reactivity relationship in the FLP-catalyzed hydrogenation of imines" Sebastian Tussing, Karl Kaupmees and Jan Paradies* Chem. Eur. J. 2016, 22, 7422–7426
The autoinduced, frustrated Lewis pair (FLP)-catalyzed hydrogenation of 16 benzene ring substituted N-benzylidene-tertbutylamines with B(2,6-F2C6H3)3 and molecular hydrogen was investigated by kinetic analysis. The pKa values for imines and for the corresponding amines were determined by quantum-mechanical methods and provided a direct proportional relationship. The correlation of the two rate constants k1 (simple catalytic cycle) and k2 (autoinduced catalytic cycle) with pKa difference between imine and amine pairs (ΔpKa) or Hammett’s σ parameter served as useful parameters to establish a structure-reactivity relationship for the FLP-catalyzed hydrogenation of imines.

[32] "Frustrated Lewis Pair-catalyzed cycloisomerization of 1,5-enynes via 5-endo-dig cyclization/protodeborylation sequence" Sergej Tamke, Zheng-Wang Qu, Nikolai A. Sitte, Ulrich Flörke, Stefan Grimme,* and Jan Paradies* Angew. Chem. 2016, 55, 4335-4339 
The first frustrated Lewis pair-catalyzed cycloisomerization of a series of 1,5-enynes was developed. The reaction proceeds via the p-activation of the alkyne and subsequent 5-endo-dig cyclization with the adjacent alkene. The presence of PPh3 was of utmost importance on the one hand to prevent side reactions (e.g. 1,1-carboboration) and on the other hand for the efficient protodeborylation to achieve the catalytic turnover. The mechanism is explained on the basis of quantum-chemical calculations which are in full agreement with the experimental observations.

[31] "Microwave-assisted FLP-catalyzed hydrogenations" S. Tussing, J. Paradies, Dalton Trans. 2015, 45, 6124-6128.

FLP-catalyzed hydrogenations of 15 substrates were compared using microwave irradiation and conventional heating. The direct comparision revealed that a rate acceleration of up to 2.5 was achieved in the presence of microwaves. This heating method is particulary promising for the hydrogenation of nitrogen-containing heterocycles. Acridine, quinines and especially 1-methyl indole were reduced very efficiently under mild conditions and only 4 bar hydrogen pressure in high yields.

[30] "Determination of the H2-activation parameters by kinetic analysis of the autoinduced FLP-catalyzed imine hydrogenation" S. Tussing, L. Greb, S. Tamke, B. Schirmer, C. Muhle-Goll, B. Luy, J. Paradies* Chem. Eur. J. 2015, 21, 8056–8059.

The frustrated Lewis pair (FLP)-catalyzed hydrogenation and deuteration of N-benzylidene-tert-butylamine (2) was kinetically investigated by using the three boranes B(C6F5)3 (1), B(2,4,6-F3-C6H2)3 (4), and B(2,6-F2-C6H3)3 (5) and the free activation energies for the H2 activation by FLP were determined. Reactions catalyzed by the weaker Lewis acids 4 and 5 displayed autoinductive catalysis arising from a higher free activation energy (2 kcal mol−1) for the H2 activation by the imine compared to the amine. Surprisingly, the imine reduction using D2 proceeded with higher rates. This phenomenon is unprecedented for FLP and resulted from a primary inverse equilibrium isotope effect.

[29] "Synthesis and Photophysical Properties of GemPhos Noble Metal Complexes" C. Sarcher, S. Bestgen, F. C. Falk, S. Lebedkin, J. Paradies, M. M. Kappes, P. W. Roesky* J. Organomet. Chem. 2015, DOI.

GemPhos, a diphosphine ligand with a rigid paracyclophane scaffold, was used to prepare complexes of the noble metals gold, palladium, and platinum. The reaction of GemPhos with [Au(tht)2][ClO4] (tht = tetrahydrothiophene) surprisingly yielded a mononuclear charge separated gold compound [(GemPhos)Au][ClO4], in which the gold atom exhibits an uncommon trigonal planar coordination geometry. Furthermore, similar palladium [(GemPhos) (PdCl2)] and platinum [(GemPhos)(PtCl2)] complexes were obtained in very good yields by the reaction of GemPhos with [MCl2(COD)] (M = Pd, Pt; COD = 1,5-cyclooctadiene) in hot DMSO. All compounds were fully characterized by analytical and spectroscopic techniques and their solid-state structures were established by single X-ray crystallography. Their photoluminescent properties were measured at low and ambient temperatures, revealing different behavior depending on the metal and coordination mode.

[28] "Frustrated Lewis Pair catalyzed Hydrosilylation and Hydrosilane mediated Hydrogenation of Fulvenes"S. Tamke, G.-C. Daniliuc, J. Paradies*  Org. Biomol. Chem. 2014, 12, 9139-9144. 

The frustrated Lewis pair (FLP) mediated hydrosilylation of pentafulvenes is described yielding allyl silanes with high regioselectivity in excellent yields. While phenyl substituted allyl silanes undergo B(C6F5)3-mediated rearrangement to vinyl silanes dimethyl derivatives experience FLP-catalyzed hydrogenantion followed by an unprecedented protodesilylation. This observation allowed the metal-free hydrogenation of 6,6-dimethylfulvene to iso-propyl cyclopentene according to a FLP-catalyzed triple domino reaction consisting of hydrosilylation, hydrogenation and protodesilylation. The mechanisms were investigated by deuteration experiments.

[27] “Ambidextrous Catalytic Access to Dithieno[3,2‑b:2′,3′‑d]thiophene (DTT) Derivatives by Both Palladium-Catalyzed C−S and Oxidative Dehydro C−H Coupling" Peter Oechsle, Jan Paradies* Org. Lett. 2014, 16, 4086–4089.

A modular two-step synthesis of dithieno[3,2-b:2′,3′-d]thiophene (DTT) derivatives by C−S cross-coupling and oxidative dehydro C−H coupling is herein described. Dibenzo[d,d′]thieno[3,2-b;4,5-b′]dithiophene (DBTDT) and associated two donor (anisyl) and acceptor (acetyl) substituted DTT derivatives were synthesized by palladium-catalyzed cross-coupling sequences in 17% to 71% yield over two steps. The 5,5′-disubstituted DTT derivatives were characterized in terms of their photophysical (UV and fluorescence spectroscopy) and electrophysical (cyclovoltammography) properties. 

[26] "Mono- versus Dinuclear Gold-Catalyzed Intermolecular Hydroamidation" J. M. Serrano-Becerra, A. F. G. Maier, S. González-Gallardo, E. Moos, C. Kaub, M. Gaffga, G. Niedner-Schatteburg, P. W. Roesky, F. Breher, J. Paradies*  Eur. J. Org. Chem. 2014, 21, 4515-4522.

Mono- and dinuclear gold catalysts were investigated in the intermolecular hydroamidation of olefins. Upon activation of [Ph3PAuCl] and [xantphos(AuCl)2] with various silver salts (AgOTf, Ag[BF4] and Ag[SbF6]), diverging reactivity of the resulting cationic gold-complexes was observed. It was found that both the binding ability of the counterion and the solvent have significant impact on the reactivity of the mono- and dinuclear complexes.

[25] "Unsymmetrical Bisphosphines for the Amidation of Aryl Chlorides: A Kinetic Study" F. C. Falk, P. Oechsle, W. R. Thiel, C.-G. Danilluc, J. Paradies * Eur. J. Org. Chem. 2014, 3637-3645.

The rate-determining step of the palladium-catalyzed amidation of 4-tolyl chloride with benzamide in the presence of unsymmetrical bisphosphines was investigated. Isostructural [2.2]¬para¬cyclophane-derived bisphosphines bearing dicyclo¬hexyl¬phos¬phino and diarylphosphino moieties were investigated as ligands in the oxidative addition and reductive elimination by kinetic studies. The reductive elimination was accelerated when a bisphosphine was applied as ligand, which contained an electron-rich and a less electron-releasing phosphino-moiety. Apart from the reductive elimination the transmetallation had most severe impact on the palladium-catalyzed amidation of aryl halides.

[24] "Metal-free dehydro Si-N cross-coupling" S. Tamke, L. Greb, J. Paradies* Chem. Commun. 2014, 50, 2318-2320.

The metal-free B(C6F5)3 catalyzed dehydrocoupling of hydrosilanes with anilines, carbazoles and indoles is reported. For anilines and carbazoles the reaction proceeds by the liberation of H2 as sole Si–N coupling byproduct. Indoles react with diphenyl(methyl) hydrosilane to N-silyl indolines with high diastereoselectively (d.r. 10:1) in excellent yields. A mechanism of this Si–N coupling/hydrogenation sequence is proposed.

[23] "Metal-free Hydrogenation of Unsaturated Hydrocarbons Employing Molecular Hydrogen" J. Paradies Angew. Chem. 2014, 126, 3624-3629; Angew. Chem. Int. Ed. 2014, 53, 3552-3557.

The metal-free activation of hydrogen by frustrated Lewis pairs (FLPs) is a valuable method for the hydrogenation of polarized unsaturated molecules ranging from imines, enamines, silyl enol ethers to heterocycles. However, one of the most important applications of hydrogenation technology is the conversion of unsaturated hydrocarbons to alkanes or alkenes. Despite the fast development of the FLP-chemistry such reactions proved as highly demanding. This Minireview will provide an overview of the basic concepts of FLP-chemistry, the challenge in the hydrogenation of unsaturated hydrocarbons and first solutions to this central transformation.

[22] "Desymmetrization of 4,6-diprotected myo-inositol" M. B. Lauber, C.-G. Daniliuc, J. Paradies* Chem. Commun. 2013, 49, 7409-7411.

The asymmetric desymmetrization of 4,6-diprotected myoinositol derivatives was achieved by a bifunctional, readily available nucleophilic catalyst. The orthogonally protected products were obtained in 80-99% yield with 90-99% ee. Such structures serve as potential enantiopure building blocks for the synthesis of myo-inositol phosphates.

[21] "Electronic Factors for low Temperature Metal-Free H2-Activation: A Kinetic and Computational Study" L. Greb, S. Tussing, B. Schirmer, I. Leito, S. Grimme, J. Paradies* Chem. Sci. 2013, 4, 2788-2796.

The frustrated Lewis pair-mediated reversible hydrogen activation is studied as a function of the electron-donor quality of a series of phosphines. The increasing acidity of the generated phosphonium species leads to a stepwise lowering of the temperature for the highly reversible H2-activation and permits concrete classification for the first time. The influence of the acid strength on the metal-free hydrogenation of selected olefins is investigated by kinetic experiments and quantum chemical calculations. Detailed information for the rate-determining steps fully support our mechanistic model of a protonation step prior to hydride transfer. The rate of hydrogenation is strongly dependent on the electronic nature of the phosphine and of the acidity of the corresponding phosphonium cation. A careful balance of these two factors provides highly efficient metal-free hydrogenation catalysts. The provided findings are used to revise the reactivity of Lewis bases in the hydrogenation of imines, one of the most recognized application of FLPs.

[20]  "Towards Functional Group Tolerance in Frustrated Lewis Pair Chemistry: Hydrogenation of Nitroolefins and Acrylates" L. Greb, C.-G. Daniliuc, K. Bergander, J. Paradies * Angew. Chem. 2013, 125, 5989-5992; Angew. Chem. Int. Ed. 2013, 52, 5876-5879.

Weak Lewis acid for high nucleophilicity: The B(2,6-F2-C6H3)3-derived hydridoborate, formed from FLP-mediated H2-activation, displayed significant hydridic character. Solid-state and solution structure analysis revealed a dihydrogen-bonded aggregate. The new FLP-system was applied as catalyst in the hydrogenation of nitroolefins and acrylates. The reduced Lewis acidity provides higher reactivity and functional group tolerance in FLP-chemistry.

[19] "Frustrated Lewis pair catalyzed hydrogenations" J. Paradies Synlett (SynPacs) 2013, 4, 777-780.

SYNPACTS: The frustrated Lewis pair (FLP) catalyzed hydrogenation of organic molecules is discussed. The saturation of polarized double bonds by FLP can be described as the nucleophilic addition of hydrides to the polar double bond prior to proton transfer. In contrast, the hydrogenation of olefins proceeds first by protonation forming a transient carbocation, which is subsequently attacked by the hydride. Both processes give rise for efficient conversion of unsaturated organic compounds by a metal-free methodology employing molecular hydrogen.

[18] "Novel Reactivity in Frustrated Lewis Pairs: Low Temperature H2-Activation and Application in the Hydrogenation of Unfunctionalized Double Bonds" L. Greb, P. Oña-Burgos, B. Schirmer, D. W. Stephan, S. Grimme,* J. Paradies* Angew. Chem. Int. Ed. 2012, 51, 10164-10168; Angew. Chem. 2012, 124, 10311-10315.

Dieser Artikel wurde zwei Mal in Chemical & Engineering News und zwei Mal in Nachrichten aus der Chemie herausgehoben:

• "Metal-Free Olefin Hydrogenations" C&EN, 2012, 90, 27.

• "Frustrated Lewis Pairs Go Hydrogenating" C&EN, 2012, 90, Issue 52, 21.

• "Kalt und Gut" Nachr. Chem. 2013, 61, 107.

• "Trendberichte 2012: Organische Chemie " Nachr. Chem. 2013, 61, 293.

Weak Nucleophiles for Strong Activation: The reversible activation of dihydrogen by an electron deficient phosphine, (C6F5)PPh2 (2), in combination with the Lewis acid B(C6F5)3 (1) at –80 °C was accomplished. Such systems exhibit novel reactivity so that the catalytic hydrogenations of double bonds were achieved according to a protonation followed by hydride attack pathway. Electron deficient phosphines and diarlyamines were demonstrated to be viable Lewis bases for the hydrogenation of double bonds allowing catalyst loadings of 10 to 5 mol%.

[17] "[2.2]Paracyclophane-derived Dinuclear Gold Complexes" C. Sarcher, A. Lühl, F. C. Falk, S. Lebedkin, M. Kühn, J. Paradies,* M. M. Kappes,* W. Klopper,* P. W. Roesky* Eur. J. Inorg. Chem. 2012, 5033-5042.

[PhanePhos(AuCl)2] and [GemPhos(AuCl)2] show a very similar ligand scaffold, but different (aurophilic vs. non-aurophilic) intramolecular Au-Au distances. Absorption and PL spectra of both compounds are quite similar. Theoretical investigations reveal that the excited states are of a different character (i.e., influenced by the Au-Au contacts). [PhanePhos(AuCl)2] and [GemPhos(AuCl)2] were also used as catalysts in the intra- and intermolecular hydroamination of alkynes. Good to quantitative conversions on a reasonable time scale were observed. The overall performance of these catalysts in the studied reactions was similar showing that the Au-Au contacts do not have a major influence on the catalytic performance.

[16] "Development of Tartaric Acid Derived Hydrogen-Bond Catalysts" M. B. Lauber, R. Fröhlich, J. Paradies* Synthesis 2012, 44, 3209-3215.

A flexible synthesis of bifunctional thiourea derivatives based on the TADDOL framework is described. Hydroxy as well as primary, secondary and tertiary amino substituted bifunctional hydrogen-bond donors were synthesized.

[15] "[2.2]Paracyclophane derived Bisphosphines for the Activation of Hydrogen by FLPs: Application in Domino Hydrosilylation/Hydrogenation of Enones" L. Greb, P. Oña-Burgos, A. Kubas, F. C. Falk, F. Breher, K. Fink, J. Paradies* Dalton Trans. 2012, 40, 9056-9060.

The heterolytic splitting of hydrogen by two types of [2.2]paracyclophane derived bisphosphines (1, 2a and 2b) in combination with tris(pentafluorophenyl)borane (3) at room temperature is described. The corresponding frustrated Lewis pairs (FLPs) exhibit different behavior in the activation of hydrogen. This results from diverse steric and electronic properties of the bisphosphines. The reactivity of the frustrated Lewis pairs was exploited in the first diastereoselective domino hydrosilylation/hydrogenation reaction catalyzed by FLPs.

[14] "Development of [2.2]Paracyclophane derived Hydrogen-Bond Receptors" J. F. Schneider, J. Paradies* Isr. J. Chem. 2012, 52, 76-91.

The development of planar-chiral hydrogen-bond donors based on the [2.2]paracyclophane scaffold is discussed. General strategies to access functionalized enantiopure [2.2]¬para-cyclophane derivatives are briefly reviewed, with the focus on suitable precursors for the synthesis of planar-chiral thiourea derivatives. The synthesis of fourteen hydrogen-bond donors is described. The interaction of four thiourea derivatives with hydrogen-bond acceptors (DMSO and tetramethyl-ammonium chloride) was investigated by 1H NMR spectroscopy and X-ray crystallography. A selection of enantio-merically pure planar-chiral derivatives was applied in asymmetric hydrogen-bond catalysis.

[13] "[2.2]Paracyclophane derivatives: Synthesis and Application in Catalysis"  J. Paradies* Synthesis 2011, 3749-3766.

Advances in the field of [2.2]paracyclophane chemistry are reviewed including syntheses, chiral resolution and application in organic synthesis. Transition-metal catalyzed as well as organocatalytic transformations are presented focus¬ing on the development of [2.2]paracyclophane derived ligands and catalysts.

[12] "A Bidentate Phosphine for the efficient Amidation of Arylchlorides" F. C. Falk, R. Fröhlich, J. Paradies* Chem. Commun. 2011, 47, 11095-11097.

Voluminous amides were coupled with deactivated, sterically hindered aryl chlorides in excellent yields providing products, which have not been efficiently accessible by transition metal catalysis so far. Application of an unsymmetric bisphosphine ligand was critical for the high catalyst activity.

[11] "Thiourea as Sulfur Surrogate in the Palladium catalyzed C-S Bond Formation" M. Kuhn, J. Paradies* Org. Lett. 2011, 13, 4100-4103.

The first C-S bond formation/cross-coupling/cyclization domino reaction using thiourea as a cheap and easy to handle dihydrosulfide surrogate has been developed. Structurally important biarylthioether, benzo[b]thiophenes, and thieno[3,2-b]thiophene scaffolds are provided in high yield.

[10] "Readily Available Hydrogen-Bond Catalysts for the Asymmetric Transfer Hydrogenation of Nitroolefins" J. F. Schneider, M. B. Lauber, V. Muhr, D. Kratzer, J. Paradies* Org. Biomol. Chem. 2011, 9, 4323-4327.

This paper focuses on readily accessible thiourea hydrogen bond catalysts derived from amino acids, whose steric and electronic features are modulated by their degree of substitution at the carbinol carbon center. These catalysts were applied in the asymmetric transfer hydrogenation of nitroolefins furnishing the chiral products in up to 99% yield and 86% enantiomeric excess. The proposed catalyst’s mode of action is supported by mechanistic investigations.

[9] "Synthesis of Planar-Chiral Thioureas" J. F. Schneider, R. Fröhlich, J. Paradies* Synthesis 2010, 3486-3492.

An efficient access to enantiopure pseudo-geminally substituted 4-amino-13-bromo[2.2]paracyclophane is described. The aminobromide was employed in cross-coupling reactions to yield arylated 4-amino[2.2]paracyclophanes. The amines were converted into enantiopure planar-chiral thioureas, which are potential hydrogen-bond donors for enantioselective organocatalysis.

[8] "Planar-Chiral Thioureas as Hydrogen-Bond Catalysts" J. F. Schneider, F. C. Falk, R. Fröhlich, J. Paradies* Eur. J. Org. Chem. 2010, 12, 2265-2269.

The first planar-chiral thiourea hydrogen-bond catalysts were synthesized from the corresponding [2.2]paracyclophanylamines. Enantiopure bifunctional thioureas operate as hydrogen-bond catalysts and display enhanced activity in comparison to their monofunctionalized derivatives.

[7] "Synthesis of Divinylsulfides" J. Paradies* Synthesis 2010, 947-942.

Arylacetylenes react with sodium sulfide in the presence of water to yield divinylsulfides. The reaction proceeds in good to excellent yield for electron-neutral and electron-deficient aromatic systems. Three selected divinylsulfide derivatives were oxidized selectively to the corresponding sulfoxides or sulfones.

[6] "Synthesis of an Organometallic Ladderane Derivative by a Dynamic Topochemical Reaction" J. Paradies, I. Greger, G. Kehr, G. Erker,* K. Bergander, R. Fröhlich Angew. Chem. 2006, 118, 7792-7795; Angew. Chem. Int. Ed. 2006, 45, 7630-7633.

Photolysis of Bis(1-methylethenyl-cyclopentadienyl)-zirconium dichloride at 0 °C with Pyrexfiltered UV light resulted in a rapid and complete intramolecular [2+2]cycloaddition reaction to yield the corresponding cyclobutylene- bridged ansa-zirconocene dichloride isomer.

[5] "Developing a Functional Group Chemistry of Organolithium Compounds: [2+2] Cycloaddition of Alkenyl-substituted Li-Cyclopentadienides" J. Paradies, G. Erker,* R. Fröhlich, Angew. Chem. 2006, 116, 3150-3153; Angew. Chem. Int. Ed. 2006, 45, 3079-3082.

Coming together at the ends:
Bis(butadienyl-cyclopentadienyl) dichlorozirconium (1) undergoes dynamic topochemical reactions upon photolysis that eventually lead to the formation of ladderane (2) derivative and the organometallic cyclooctadiene derivative (3).

[4] “Insertion Reactions at Cyclobutylene-Bridged ansa-Metallocene Complexes: A Quest for the Influence of Covering Phenylene Units” L. Chen, W.-L. Nie, J. Paradies, G. Kehr, R. Fröhlich, K. Wedeking, G. Erker* Organometallics, 2006, 25, 5333-5344.

The cyclobutylene-bis(2-indenyl)zirconium dichloride complex, derived from an intramolecular photochemical [2+2] cycloaddition reaction of bis[2-(methylethenyl)indenyl]zirconium dichloride, was reacted with methyllithium or phenyllithium to yield the corresponding cyclobutylene-bis(2-indenyl)- zirconium dimethyl or diphenyl complex, respectively.

[3] "Observation of Two Consecutive Photoreactions Upon UV-Irradiation of a Bis(1,3-dialkenyl-Cp)zirconium Complex" J. Paradies, R. Fröhlich, G. Kehr, G. Erker* Organometallics 2006, 25, 3920-3925.

Photolysis of bis[1,3-di(1-methylethenyl)C5H3]zirconium dichloride with Pyrex-filtered UV/vis light at ambient temperature led to a rapid intramolecular [2+2]- cycloaddition reaction to yield a 1:1 mixture of the meso- and rac-isomers of the corresponding singly cyclo-butylene-bridged ansa-metallocene system. Photolysis of this mixture with quartz-filtered UV light at -80 °C very slowly converted meso-4a to rac-4a. Over 2 days a 12:1 ratio of rac/meso-4a was achieved under these conditions.

[2] “Developing a Functional Group Chemistry of Organolithium Compounds: [2+2] Cycloaddition of Alkenyl-substituted Li-Cyclopentadienides” J. Paradies, G. Erker,* R. Fröhlich Angew. Chem. 2006, 116, 3150-3153; Angew. Chem., Int. Ed. Engl. 2006, 45, 3079-3082.

Li and light:
Alkenyl-substituted lithium cyclopentadienides, which are in equilibrium with the substituted lithocene anion structure 1, undergo a photochemical [2+2] cycloaddition to yield selectively the carbon-carbon coupling product 2. This is a rare case of organic functional-group chemistry for a reactive organolithium compound.

[1] "Photogeneration of Titanium(III) from Titanium(IV) Citrate in Aqueous Solution" J. Paradies, J. Crudass, F. MacKay, L. J. Yellowlees, J. Montgomery, S. Parsons, L. Oswald, N. Robertson, P. J. Sadler* J. Inorg. Biochem. 2006, 100, 1260-1264.

We show that Ti(III) citrate is generated in a facile manner and in good yield by the action of UV radiation on Ti(IV) citrate in aqueous solution. The Ti(III)-citrate species formed was isolated and characterised by UV–Visible spectroscopy, showing an absorption at 547 nm (e = 100 M1 cm1), and by electron paramagnetic resonance (EPR) spectroscopy giving a resonance at g = 1.949 (linewidth = 60 G).

Group Leader

Prof. Dr. Jan Paradies

Organische Chemie - Arbeitskreis Paradies

Group Leader

Jan Paradies
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+49 5251 60-5770
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