Indolyl Phosphine Nickel(II) Fluorido Complexes: Synthesis and Intermediates in Suzuki–Miyaura Cross-Coupling Reactions |
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| Authors: | Ouchan He Beatrice Cula Thomas Braun |
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| Institution: | Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, DE-12489 Berlin, Germany |
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| Abstract: | The C?F bond activation of pentafluoropyridine and 2,3,5,6-tetrafluoropyridine at Ni(cod)2] (cod=1,5-cyclooctadiene) in the presence of the phosphine PPh2(Ind) (Ind=3-methyl-2-indolyl) led to the formation of the nickel(II) fluorido bis(phosphine) complexes trans-Ni(F)(2-C5NF4){PPh2(Ind)}2] and trans-Ni(F)(2-C5HNF3){PPh2(Ind)}2]. The complexes are characterized by the presence of intramolecular hydrogen bonds between the NH group of the phosphine ligands and the fluorido ligand. Stochiometric model reactions of nickel(II) fluorido complexes with PhB(OH)2 revealed that the former can be considered as intermediates in Suzuki–Miyaura cross coupling reactions. Catalytic experiments were attempted using 10 mol-% of trans-Ni(F)(2-C5NF4){PPh2(Ind)}2] as catalyst and the activities of the PPh2(Ind) complex were compared to the ones of an analogous nickel(II) fluorido complex, bearing PPh3 instead of PPh2(Ind) as ligands. The latter exhibited a somewhat lower catalytic activity suggesting a slight influence of the H-bonds in the outer coordination sphere. |
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| Keywords: | C?F activation fluorido complexes fluorine intramolecular hydrogen bonds nickel Suzuki–Miyaura coupling |
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