03 Fakultät Chemie

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4

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Institute: search.filters.UBSInstitut.Deutsche Institute für Textil- und Faserforschung Denkendorf (DITF)Author: search.filters.author.Frey, Wolfgang

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Now showing 1 - 7 of 7
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    Reversible N‐heterocyclic carbene‐induced α‐H abstraction in Tungsten(VI) imido dialkyl dialkoxide complexes
    (2020) Musso, Janis V.; Benedikter, Mathis J.; Wang, Dongren; Frey, Wolfgang; Altmann, Hagen J.; Buchmeiser, Michael R.
    The first reversible N‐heterocyclic carbene (NHC) induced α‐H abstraction in tungsten(VI) imido‐dialkyl dialkoxide complexes is reported. Treatment of W(NAr)(CH2Ph)2(OtBu)2 (Ar=2,6‐dichlorophenyl, 2,6‐dimethylphenyl, 2,6‐diisopropylphenyl) with different NHCs leads to the formation of complexes of the type W(NAr)(CHPh)(NHC)(CH2Ph)(OtBu) in excellent isolated yields of up to 96 %. The highly unusual release of the tert‐butoxide ligand as tBuOH in the course of the reaction was observed. The formed alkylidene complexes and tBuOH are in an equilibrium with the NHC and the dialkyl complexes. Reaction kinetics were monitored by 1H NMR spectroscopy. A correlation between the steric and electronic properties of the NHC and the reaction rates was observed. Kinetics of a deuterium‐labeled complex in comparison to its non‐deuterated counterpart revealed the presence of a strong primary kinetic isotope effect (KIE) of 4.2, indicating that α‐H abstraction is the rate‐determining step (RDS) of the reaction.
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    Chromium(VI) bisimido dichloro, bisimido alkylidene, and chromium(V) bisimido iodo N‐heterocyclic carbene complexes
    (2020) Panyam, Pradeep K. R.; Stöhr, Laura; Wang, Dongren; Frey, Wolfgang; Buchmeiser, Michael R.
    Reaction of CrCl2(N-tBu)2 with 1,3-dimethylimidazol-2-ylidene (IMe), 1,3-dimethyl-4,5-dichloroimidazol-2-ylidene (IMeCl2), 1,3-di(2-propyl)imidazol-2-ylidene (IPr), 1,3-dimesitylimidazol-2-ylidene (IMes) and 1,3-bis(2,6-(2-Pr)2C6H3)imidazol-2-ylidene (IDipp) yields the corresponding N-heterocyclic carbene (NHC) adducts CrCl2(IMe)(N-tBu)2 (1), CrCl2(IMeCl2)(N-tBu)2 (2), CrCl2(IPr)(N-tBu)2 (3), CrCl2(IMes)(N-tBu)2 (4) and CrCl2(IDipp)(N-tBu)2 (5). Likewise, reaction of CrCl2(N-2,6-(2-Pr)2C6H3)2 and CrCl2(N-adamantyl)2 with IMes yields CrCl2(N-2,6-(2-Pr)2C6H3)2(IMes) (6) and CrCl2(N-adamantyl)2(IMes) (7), respectively. Reaction of CrCl2(N-tBu)2 with the bidentate NHCs 1-R-3-(1-(2-LiO-C6H4))imidazol-2-ylidene yields the corresponding pentacoordinated Cr(VI) complexes CrCl2(1-R-3-(1-(2-O-C6H4))imidazol-2-ylidene)2C6H3)2(IMes) (R = 2,4,6-(CH3)3C6H2, 8), (R = tBu, 9), (R = 2-phenyl-C6H4, 10). Reaction of the chromium(VI) complex Cr(N-2,6-(2-Pr)2-C6H3)2(CH2C(CH3)3)2 with 1,3-dimethylimidazol-2-ylidene·AgI yields the bimetallic silver adduct of the chromium alkylidene complex (11) along with the tetrahedral chromium(V) complex CrI(N-2,6-(2-Pr)2-C6H3)2(1,3-dimethylimidazol-2-ylidene) (12). Compounds 1-4, 7, 9-12 were characterized by single-crystal X-ray analysis. Finally, the chromium(VI) bisimido-amido complexes 13-14 bearing the N-6-(2-(diethylboryl)phenyl)pyridyl-2-yl-motif are reported.
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    Predicting catalytic activity from 13CCH alkylidene chemical shift in cationic tungsten oxo alkylidene N‐heterocyclic carbene complexes
    (2021) Musso, Janis V.; Schowner, Roman; Falivene, Laura; Frey, Wolfgang; Cavallo, Luigi; Buchmeiser, Michael R.
    A series of cationic tungsten oxo alkylidene N‐heterocyclic carbene (NHC) complexes was synthesized and structurally characterized by single crystal X‐ray diffraction. The 13C NMR chemical shifts of the alkylidene C atoms of these complexes were correlated with the diamagnetic, paramagnetic and spin‐orbit chemical shifts calculated by DFT. A good correlation (R2=0.90) between the DFT isotropic chemical shifts and the experimental chemical shift as well as a strong correlation between the DFT isotropic chemical shifts and the TOF1min for the RCM of 1,7‐octadiene was found. Further, a comparison of the catalyst geometries allowed for assigning tetracoordinate pseudotetrahedral catalysts to the most deshielded alkylidenes and to the highest TOF1min, pentacoordinate square‐planar catalysts to the intermediate deshielded alkylidenes and intermediate TOF1min, and hexacoordinate and octahedral catalyst to the most shielded alkylidene and lowest TOF1min. Analysis of the magnetic shielding tensors allowed for ascribing variations in the chemical shifts to electronic transitions between occupied molecular orbitals corresponding to the alkylidene‐C and alkylidene‐H σ‐bonds and the empty molecular orbital corresponding to the W‐alkylidene σ*‐bond.
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    A sodium bis(perfluoropinacol) borate-based electrolyte for stable, high-performance room temperature sodium-sulfur batteries based on sulfurized poly(acrylonitrile)
    (2021) Murugan, Saravanakumar; Klostermann, Sina V.; Frey, Wolfgang; Kästner, Johannes; Buchmeiser, Michael R.
    A new type of electrolyte salt based on a weakly coordinating anion (Na-PPB) for RT Na-SPAN batteries has been developed. Na-PPB was synthesized in bulk via a one-pot reaction. NMR spectroscopy reveals high purity of the salt and stability even under ambient atmospheric conditions. Single-crystal X-ray analysis confirmed the molecular structure of Na-PPB with Na+ coordinated by one DME molecule. The electrolyte containing Na-PPB with PC + 10 wt% FEC showed high oxidative stability on Al current collector exceeding 5.5 V. In a Na-SPAN cell, the Na-PPB electrolyte allows for an initial and final discharge capacity (500 cycles) of 1140 mAh/gsulfur and 965 mAh/gsulfur respectively, obtained at 2C (3.35 A/gsulfur). The excellent electrochemical performance and good chemical stability of Na-PPB offers access to the design of novel electrolyte salts for RT Na-SPAN batteries.
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    Molybdenum alkylidyne silyloxy N‐heterocyclic carbene complexes : highly active alkyne metathesis catalysts that can be handled in air
    (2022) Musso, Janis V.; Gramm, Vincent; Stein, Sarjano; Frey, Wolfgang; Buchmeiser, Michael R.
    A series of molybdenum alkylidyne silyloxy N‐heterocyclic carbene (NHC) complexes of the general formula [Mo(≡C(R))(OSiPh3)3(NHC)] (R=tBu, 4‐methoxyphenyl, 2,4,6‐trimethylphenyl; NHC = 1,3‐diisopropylimidazol‐2‐ylidene, 1,3‐dicyclohexylimidazol‐2‐ylidene, 1,3‐dicyclohexyl‐4,5‐dihydroimidazol‐2‐ylidene, 1,3‐dimethylimidazol‐2‐ylidene, 1,3‐dimethyl‐4,5‐dichloroimidazol‐2‐ylidene) was synthesized. Single crystal X‐ray analyses revealed that with increasing steric demand of the alkylidyne group, enhanced air‐stability of the complexes in the solid‐state is achieved with the most stable complex (R=2,4,6‐trimethylphenyl, NHC = 1,3‐diisopropylimidazol‐2‐ylidene) being stable in air for 24 h without showing signs of decomposition in 1H NMR. In contrast to previously reported air‐stable molybdenum‐based complexes, the novel catalysts proved to be highly active in alkyne metathesis, allowing for turnover numbers (TONs) of up to 6000 without further activation, and tolerant towards several functional groups such as tosyl, ether, ester, thioether and nitro moieties. Their air stability allows for facile handling of the catalysts in air and even after exposure to ambient atmosphere for one week, the most stable representative still displayed high productivity in alkyne metathesis.
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    Synthetic and structural peculiarities of neutral and cationic molybdenum imido and tungsten oxo alkylidene complexes bearing weakly coordinating N‐heterocyclic carbenes
    (2024) Buchmeiser, Michael R.; Wang, Dongren; Schowner, Roman; Stöhr, Laura; Ziegler, Felix; Sen, Suman; Frey, Wolfgang
    The syntheses of the neutral molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes of the general formula [Mo(NAr)(CHCMe2Ph)(NHC)XY] (Ar=2-tBu-C6H4, 2-CF3-C6H4, 2,6-Me2-C6H3, 2,6-Cl2-C6H3, adamantyl; X, Y=OTf, OC(CF3)3, OCH(CF3)2, OC6F5, SC6F5, 2,5-bis(pentafluorophenyl)phen-1-yl) bearing electron-withdrawing NHCs (1,3-dimethyl-4,5-dichloroimidazol-2-ylidene (IMeCl2), 1,3,4-triphenyl-1,2,4-triazol-5-ylidene (TPT)) are reported. Complementary, the corresponding cationic molybdenum imido alkylidene NHC complexes of the general formula [Mo(NAr)(CHCMe2R)(NHC)X+][B(ArF)4−/Al(OC(CF3)3)4−] (R=Me, Ph; B(ArF)4-=tetrakis (3,5-bis(trifluoromethyl)phenyl)borate) have been prepared. Aiming at tungsten oxo complexes, reaction of [W(O)Cl2(CHCMe2Ph)(PMe2Ph)2] with [1,3-dimethyl-4,5-dichloroimidazol-2-ylidene⋅AgI] (IMeCl2⋅AgI) followed by the addition of lithium terphenoxide yields [W(O)(CHCMe2Ph)(IMeCl2)(DPPO)2]. For comparison, [W(O)Cl(CHCMe2Ph)(IMes)(OSi(OtBu)3)] was prepared via reaction of [W(O)Cl2(CHCMe2Ph)(PMe2Ph)(IMes)] with KOSi(OtBu)3. [W(O)(CHCMe2Ph)(IMeCl2)(DPPO)(Et2O)+][B(ArF)4−] (DPPO=2,6-diphenylphenoxide) became accessible via reaction of [W(O)(DPPO)2(CHCMe2Ph)(IMeCl2)] with anilinium B(ArF)4-. The structural peculiarities of selected complexes are reported. Benchmark ring-closing metathesis and homometathesis reactions revealed that the neutral complexes bearing weakly coordinating NHCs such as IMeCl2 and TPT possessed only moderate activity, which could, however, be improved by preparing the corresponding cationic metal alkylidene complexes.
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    Neutral and cationic molybdenum imido alkylidene cyclic alkyl amino carbene (CAAC) complexes for olefin metathesis
    (2023) Kundu, Koushani; Musso, Janis V.; Benedikter, Mathis J.; Frey, Wolfgang; Gugeler, Katrin; Kästner, Johannes; Buchmeiser, Michael R.
    The first neutral and cationic Mo imido alkylidene cyclic alkyl amino carbene (CAAC) complexes of the general formulae [Mo(N-Ar)(CHCMe2Ph)(X)2(CAAC)] and [Mo(N−Ar)(CHCMe2Ph)(X)(CAAC)][B(ArF)4] (X=Br, Cl, OTf, OC6F5; CAAC=1-(2,6-iPr2-C6H3)-3,3,5,5-tetramethyltetrahydropyrrol-2-ylidene) have been synthesized from molybdenum imido bishalide alkylidene DME precursors. Different combinations of the imido and “X” ligands have been employed to understand synthetic peculiarities. Selected complexes have been characterized by single-crystal X-ray analysis. Due to the pronounced σ-donor/π-acceptor characteristics of CAACs, the corresponding neutral and cationic molybdenum imido alkylidene CAAC complexes do not require the presence of stabilizing donor ligands such as nitriles. Calculations on the PBE0-D3BJ/def2-TZVP level for PBE0-D3BJ/def2-SVP optimized geometries revealed partial charges at molybdenum similar to the corresponding molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes with a slightly higher polarization of the molybdenum alkylidene bond in the CAAC complexes. All cationic complexes have been tested in olefin metathesis reactions and showed improved activity compared to the analogous NHC complexes for hydrocarbon-based substrates, allowing for turnover numbers (TONs) up to 9500 even at room temperature. Some Mo imido alkylidene CAAC complexes are tolerant towards functional groups like thioethers and sulfonamides.