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- ItemSynthetic strategies to bicyclic tetraphosphanes using P1, P2 and P4 building blocks(London : Soc., 2015) Bresien, Jonas; Faust, Kirill; Hering-Junghans, Christian; Rothe, Julia; Schulz, Axel; Villinger, AlexanderDifferent reactions of Mes* substituted phosphanes (Mes* = 2,4,6-tri-tert-butylphenyl) led to the formation of the bicyclic tetraphosphane Mes*P4Mes* (5) and its unknown Lewis acid adduct 5·GaCl3. In this context, the endo–exo isomer of 5 was fully characterized for the first time. The synthesis was achieved by reactions involving “self-assembly” of the P4 scaffold from P1 building blocks (i.e. primary phosphanes) or by reactions starting from P2 or P4 scaffolds (i.e. a diphosphene or cyclic tetraphosphane). Furthermore, interconversion between the exo–exo and endo–exo isomer were studied by 31P NMR spectroscopy. All compounds were fully characterized by experimental as well as computational methods.
- ItemMetal/Metal Redox Isomerism Governed by Configuration(Weinheim : Wiley-VCH, 2020) Ludwig, Stephan; Helmdach, Kai; Hettenschmidt, Mareike; Oberem, Elisabeth; Rabeah, Jabor; Villinger, Alexander; Ludwig, Ralf; Seidel, Wolfram W.A pair of diastereomeric dinuclear complexes, [Tp′(CO)BrW{μ-η2-C,C′-κ2-S,P-C2(PPh2)S}Ru(η5-C5H5)(PPh3)], in which W and Ru are bridged by a phosphinyl(thiolato)alkyne in a side-on carbon P,S-chelate coordination mode, were synthesized, separated and fully characterized. Even though the isomers are similar in their spectroscopic properties and redox potentials, the like-isomer is oxidized at W while the unlike-isomer is oxidized at Ru, which is proven by IR, NIR and EPR-spectroscopy supported by spectro-electrochemistry and computational methods. The second oxidation of the complexes was shown to take place at the metal left unaffected in the first redox step. Finally, the tipping point could be realized in the unlike isomer of the electronically tuned thiophenolate congener [Tp′(CO)(PhS)W{μ-η2-C,C′-κ2-S,P-C2(PPh2)S}Ru(η5-C5H5)-(PPh3)], in which valence trapped WIII/RuII and WII/RuIII cationic species are at equilibrium. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemOn Silylated Oxonium and Sulfonium Ions and Their Interaction with Weakly Coordinating Borate Anions(Weinheim : Wiley-VCH, 2019) Bläsing, Kevin; Labbow, Rene; Michalik, Dirk; Reiß, Fabian; Schul, Axel; Villinger, Alexander; Walker, SvenjaAttempts have been made to prepare salts with the labile tris(trimethylsilyl)chalconium ions, [(Me3Si)3E]+ (E=O, S), by reacting [Me3Si-H-SiMe3][B(C6F5)4] and Me3Si[CB] (CB−=carborate=[CHB11H5Cl6]−, [CHB11Cl11]−) with Me3Si-E-SiMe3. In the reaction of Me3Si-O-SiMe3 with [Me3Si-H-SiMe3][B(C6F5)4], a ligand exchange was observed in the [Me3Si-H-SiMe3]+ cation leading to the surprising formation of the persilylated [(Me3Si)2(Me2(H)Si)O]+ oxonium ion in a formal [Me2(H)Si]+ instead of the desired [Me3Si]+ transfer reaction. In contrast, the expected homoleptic persilylated [(Me3Si)3S]+ ion was formed and isolated as [B(C6F5)4]− and [CB]− salt, when Me3Si-S-SiMe3 was treated with either [Me3Si-H-SiMe3][B(C6F5)4] or Me3Si[CB]. However, the addition of Me3Si[CB] to Me3Si-O-SiMe3 unexpectedly led to the release of Me4Si with simultaneous formation of a cyclic dioxonium dication of the type [Me3Si-μO-SiMe2]2[CB]2 in an anion-mediated reaction. DFT studies on structure, bonding and thermodynamics of the [(Me3Si)3E]+ and [(Me3Si)2(Me2(H)Si)E]+ ion formation are presented as well as mechanistic investigations on the template-driven transformation of the [(Me3Si)3E]+ ion into a cyclic dichalconium dication [Me3Si-μE-SiMe2]22+. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemCorrection: Increasing steric demand through flexible bulk – primary phosphanes with 2,6-bis(benzhydryl)phenyl backbones(London : Soc., 2019) Bresien, Jonas; Goicoechea, Jose M.; Hinz, Alexander; Scharnhölz, Moritz T.; Schulz, Axel; Suhrbier, Tim; Villinger, AlexanderCorrection for 'Increasing steric demand through flexible bulk-primary phosphanes with 2,6-bis(benzhydryl)phenyl backbones' by Jonas Bresien et al., Dalton Trans., 2019, 48, 3786-3794. © 2019 The Royal Society of Chemistry.
- ItemThree in One: The Versatility of Hydrogen Bonding Interaction in Halide Salts with Hydroxy-Functionalized Pyridinium Cations(Weinheim : Wiley-VCH Verl., 2021) Al Sheakh, Loai; Niemann, Thomas; Villinger, Alexander; Stange, Peter; Zaitsau, Dzmitry H.; Strate, Anne; Ludwig, RalfThe paradigm of supramolecular chemistry relies on the delicate balance of noncovalent forces. Here we present a systematic approach for controlling the structural versatility of halide salts by the nature of hydrogen bonding interactions. We synthesized halide salts with hydroxy-functionalized pyridinium cations [HOCn Py]+ (n=2, 3, 4) and chloride, bromide and iodide anions, which are typically used as precursor material for synthesizing ionic liquids by anion metathesis reaction. The X-ray structures of these omnium halides show two types of hydrogen bonding: 'intra-ionic' H-bonds, wherein the anion interacts with the hydroxy group and the positively charged ring at the same cation, and 'inter-ionic' H-bonds, wherein the anion also interacts with the hydroxy group and the ring system but of different cations. We show that hydrogen bonding is controllable by the length of the hydroxyalkyl chain and the interaction strength of the anion. Some molten halide salts exhibit a third type of hydrogen bonding. IR spectra reveal elusive H-bonds between the OH groups of cations, showing interaction between ions of like charge. They are formed despite the repulsive interaction between the like-charged ions and compete with the favored cation-anion H-bonds. All types of H-bonding are analyzed by quantum chemical methods and the natural bond orbital approach, emphasizing the importance of charge transfer in these interactions. For simple omnium salts, we evidenced three distinct types of hydrogen bonds: Three in one!
- ItemCationic clustering influences the phase behaviour of ionic liquids(London : Nature Publishing Group, 2018) Niemann, Thomas; Zaitsau, Dimitri; Strate, Anne; Villinger, Alexander; Ludwig, Ralf“Unlike charges attract, but like charges repel”. This conventional wisdom has been recently challenged for ionic liquids. It could be shown that like-charged ions attract each other despite the powerful opposing electrostatic forces. In principle, cooperative hydrogen bonding between ions of like-charge can overcome the repulsive Coulomb interaction while pushing the limits of chemical bonding. The key challenge of this solvation phenomenon is to establish design principles for the efficient formation of clusters of like-charged ions in ionic liquids. This is realised here for a set of well-suited ionic liquids including the same hydrophobic anion but different cations all equipped with hydroxyethyl groups for possible H-bonding. The formation of H-bonded cationic clusters can be controlled by the delocalization of the positive charge on the cations. Strongly localized charge results in cation-anion interaction, delocalized charge leads to the formation of cationic clusters. For the first time we can show, that the cationic clusters influence the properties of ILs. ILs comprising these clusters can be supercooled and form glasses. Crystalline structures are obtained only, if the ILs are dominantly characterized by the attraction between opposite-charged ions resulting in conventional ion pairs. That may open a new path for controlling glass formation and crystallization. The glass temperatures and the phase transitions of the ILs are observed by differential scanning calorimetry (DSC) and infrared (IR) spectroscopy.
- ItemCycloaddition of Alkenes and Alkynes to the P-centered Singlet Biradical [P(μ-NTer)]2(Weinheim : Wiley-VCH, 2020) Chojetzki, Lukas; Schulz, Axel; Villinger, Alexander; Wustrack, RonaldThe reaction of biradical [P(μ-NTer)]2 (1, Ter = 2,6-bis(2,4,6-trimethylphenyl)phenyl) towards different alkenes (R = 2,3-dimethyl–butadiene, 2,5-dimethyl-2,4-hexadiene, 1,7-octadiene, 1,4-cyclohexadiene) and alkynes (R = 1,4-diphenyl-1,3-butadiyne) was studied experimentally. Although these olefins can react in different ways, only [2+2] cycloaddition products (1R) were observed. The reaction with 2,3-dimethylbutadiene also led to the [2+2] product (1dmb). Thermal treatment of 1dmb above 140 °C resulted in the recovery of biradical 1 upon homolytic bond cleavage of the two P–C bonds and the release of 2,3-dimethylbutadiene. In contrast to this reaction, all other [2+2] additions products (1R, R = 1,7-octadiene, 1,4-cyclohexadiene, 1,4-diphenyl-1,3-butadiyne) began to decompose at temperatures between 200 °C and 300 °C. Only unidentified products were obtained but no temperature-controlled equilibrium reactions were observed. Computations were carried out to shed light into the formal [2+2] as well as the possible [4+2] addition reaction.
- ItemAzadiphosphaindane-1,3-diyls: A Class of Resonance-Stabilized Biradicals(Weinheim : Wiley-VCH, 2021) Bresien, Jonas; Michalik, Dirk; Schulz, Axel; Villinger, Alexander; Zander, EdgarConversion of 1,2-bis(dichlorophosphino)benzene with sterically demanding primary amines led to the formation of 1,3-dichloro-2-aza-1,3-diphosphaindanes of the type C6H4(μ-PCl)2N-R. Reduction yielded the corresponding 2-aza-1,3-diphosphaindane-1,3-diyls (1), which can be described as phosphorus-centered singlet biradical(oid)s. Their stability depends on the size of the substituent R: While derivatives with R=Dmp (2,6-dimethylphenyl) or Ter (2,6-dimesitylphenyl) underwent oligomerization, the derivative with very bulky R=tBuBhp (2,6-bis(benzhydryl)-4-tert-butylphenyl) was stable with respect to oligomerization in its monomeric form. Oligomerization involved activation of the fused benzene ring by a second equivalent of the monomeric biradical and can be regarded as formal [2+2] (poly)addition reaction. Calculations indicate that the biradical character in 1 is comparable with literature-known P-centered biradicals. Ring-current calculations show aromaticity within the entire ring system of 1. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
- ItemOn New Staudinger Type Reactions of Phosphorus Centered Biradicaloids, [P(μ-NR)]2 (R = Ter, Hyp), with Ionic and Covalent Azides(Weinheim : Wiley-VCH, 2020) Schulz, Axel; Hinz, Alexander; Rölke, Anne; Villinger, Alexander; Wustrack, RonaldPhosphorus centered biradicaloids of the type [P(μ-NTer)]2 [R = Ter = terphenyl = 2,6-bis(2,4,6-trimethylphenyl)phenyl, Hyp = tris(trimethylsilyl)silyl] were treated with covalent (R-N3) and ionic azides (AgN3 and Hg(N3)2). While the reaction with the ionic azides led exclusively to the formation of diazides, [N3P(μ-NTer)]2, triaza-diphospha-pentadienes, RN=P–N(R')–P=NR, were observed in the reaction with covalent azides featuring a Staudinger type reaction followed by PN bond rearrangement reactions. This new Staudinger type mechanism as well as the structure, bonding and thermodynamics along different reaction paths are discussed based on DFT computations.
- ItemLow temperature isolation of a dinuclear silver complex of the cyclotetraphosphane [ClP(μ-PMes*)]2(London : Soc., 2015) Bresien, Jonas; Schulz, Axel; Villinger, AlexanderThe reaction of the cyclotetraphosphane [ClP(μ-PMes*)]2 (1, Mes* = 2,4,6-tri-tert-butylphenyl) with Ag[Al(ORF)4] (RF = CH(CF3)2) resulted in a labile, dinuclear silver complex of 1, which eliminates AgCl above −30 °C. Its properties were investigated by spectroscopic methods, single crystal X-ray diffraction and DFT calculations.