03 Fakultät Chemie

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Author: search.filters.author.Benedikter, Mathis J.Subject: search.filters.subject.660

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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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    Dual catalysis with an N‐heterocyclic carbene and a Lewis acid : thermally latent precatalyst for the polymerization of ε‐caprolactam
    (2020) Altmann, Hagen J.; Steinmann, Mark; Elser, Iris; Benedikter, Mathis J.; Naumann, Stefan; Buchmeiser, Michael R.
    So far, the earlier reported strong correlation between basicity of an N‐heterocyclic carbene (NHC) and its reactivity in poly(ε‐caprolactam) (PA6) synthesis resulted in a substantial limitation of applicable carbenes. Here, to overcome this issue, 1,3‐dimethylimidazolium‐2‐carboxylate, an easily accessible, air and moisture‐stable NHC, was applied as thermally latent initiator. In order to compensate for its low basicity, reactivity was enhanced by the addition of both a Lewis acid and an activator to ease the initial polymerization step. The resulting mixtures of ε‐caprolactam, the CO2‐protected NHC, a Lewis acid and N‐acylazepan‐2‐one constitute homogeneous, thermally fully latent “single‐component” blends for the anionic polymerization‐based synthesis of PA6. They can be stored both in the liquid and solid state for days and months, respectively, without any loss in activity. The role of the Lewis acid as well as technical implications of the prolonged pot‐times are discussed.