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Author: Fischer, Fabian × Subject: Cycloaddition ×

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    CpCo(i) precatalysts for [2 + 2 + 2] cycloaddition reactions : Synthesis and reactivity
    (London : RSC Publ., 2020) Fischer, Fabian; Pientka, Tobias; Jiao, Haijun; Spannenberg, Anke; Hapke, Marko
    The efficient synthesis and structural characterisation of a series of novel CpCo(i)-olefin-phosphite/phosphoramidite complexes and their evaluation in catalytic cyclotrimerisation reactions are reported. The protocol for precatalyst synthesis is widely applicable to different P-containing ligands, especially phosphites and phosphoramidites, as well as acyclic and cyclic olefins. A selection of the prepared complexes was investigated towards their catalytic performance in [2 + 2 + 2] cycloaddition reactions of diynes and nitriles, as well as triynes. While revealing significant differences in reactivity, the most reactive precatalysts work even already at 75 °C. One of these precatalysts also proved its potential in exemplary (co)cyclotrimerisations towards functionalised pyridines and benzenes. The energetics of complex formation and exemplary ligand exchange with a substrate diyne were elucidated by theoretical calculations and compared with the catalytic reactivity. © 2020 The Royal Society of Chemistry.
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    Air-Stable CpCoI–Phosphite–Fumarate Precatalyst in Cyclization Reactions: Comparing Different Methods of Energy Supply
    (Weinheim : Wiley-VCH Verl., 2018) Fischer, Fabian; Hapke, Marko
    The robust CoI precatalyst [CpCo(P{OEt}3)(trans-MeO2CHC=CHCO2Me)] was investigated in cyclotrimerizations, furnishing benzenes and pyridines from triynes, diynes and nitriles, comparing the influence of different ways of energy supply; namely, irradiation and conventional (thermal) or microwave heating. The precatalyst was found to work under all conditions, including the possibility to catalyze cyclotrimerizations at room temperature under photochemical conditions at longer reaction times. Performance of the reactions in a microwave reactor proved to be the most time-efficient way to rapidly assemble the expected reaction products; however, careful selection of reaction conditions can be required. The synthesis of pyridines and isoquinolines successfully involved the utilization of versatile functionalized nitriles, affording structurally interesting reaction products. Comparison with the known and often applied precatalyst CpCo(CO)2 demonstrated the significantly higher reactivity of the CpCoI–phosphite–olefin precatalyst.