Abstract
Monovalent NHC-nickel complexes bearing triarylphosphine, in which fluorine is incorporated onto the aryl groups, have been synthesized. Tris(3,5-di(trifluoromethyl)-phenyl)phosphine efficiently gave a monovalent nickel bromide complex, whose structure was determined by X-ray diffraction analysis for the first time. In the solid state, the Ni(I) complex was less susceptible to oxidation in air than the triphenylphosphine complex, indicating greatly improved solid-state stability. In contrast, the Ni(I) complex in solution can easily liberate the phosphine, high catalytic activity toward the Kumada–Tamao–Corriu coupling of aryl bromides.
Highlights
Recent developments in the field of nickel catalysis have opened up possibilities of new catalytic processes directly involving monovalent nickel complexes in organometallic chemistry [1,2,3,4,5,6] along with those involving conventional zerovalent nickel catalysts
P(C6 F5 )3 did not coordinate to nickel, resulting in the complete recovery of the starting materials under the reaction conditions. This may be attributed to steric repulsion between a pair of diisopropylphenyl groups of the IPr ligand and pentafluorophenyl groups of P(C6 F5 )3, where the cone angle (184◦ ) is greater than that of P(Arm-CF3 )3 (160◦ )
F and F were found to be gathered in layers in the crystalline state
Summary
Recent developments in the field of nickel catalysis have opened up possibilities of new catalytic processes directly involving monovalent nickel complexes in organometallic chemistry [1,2,3,4,5,6] along with those involving conventional zerovalent nickel catalysts. Several studies have used well-defined nickel(I) complexes as catalyst precursors [8,9,10,11,12,13,14], and reactions where nickel(I) complexes are the key intermediates have been proposed based on theoretical calculations [15,16,17,18,19,20]. One of the current bottlenecks in nickel(I) catalysis research is developing catalytically active, air-stable nickel(I) catalyst precursors. It is safe to say that a breakthrough here would go a long way in furthering our knowledge about nickel catalyst chemistry
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