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Novel catalytic properties of pyridyl-bonded Pd-catalysts in cross-couplings of aryl halides with phenyl boronic acid under aerobic conditions
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DOI：10.1039/D6RA02949C.png)
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Abstract
En 中文
A new series of stable; easily accessible; efficient and recyclable phosphine free Pd-catalysts have been developed for their catalytic activity using Suzuki–Miyaura cross-coupling as model reaction system. The 2-benzoylpyridine-N(4)-substitutedthiosemicarbazones form compounds of composition; [Pd{(2-py-N)(Ph)CN–NC(–S)–N4HR}Cl] (R =H; Me; Et; Ph); which have been labeled as Cat 1(H); Cat 2(Me); Cat 3(Et) and Cat 4(Ph) – based on R-substitution at –N4HR. The catalytic activity of these complexes with central core; {Pd(NNS-L)Cl}; has been explored by using simple aryl bromides and aryl iodides as substrates for S-M coupling reactions. Thus the C–C cross-couplings of a series of aryl halides (R–X); Ph–X; p-NC–C6H4–X; p-MeO–C6H4–X and p-Me–C6H4–X (X = Br; I); with phenyl boronic acid have been successfully carried out in the presence of a Pd-catalyst using K2CO3 base in aqueous ethanol medium at 50 °C under aerobic conditions. Each catalyst activated C–Br and C–I bonds of aryl halides and formed di-aryl products; Ph–Ph; p-NC–C6H4–Ph; p-MeO–C6H4–Ph and p-H3C–C6H4–Ph; from both type of halides with high isolated yields and TON. The reactivity of C–X bonds of aryl halides (Y–C6H4–X; X = Br; I) towards oxidation addition varied in the order: Y = CN > H > MeO ∼ Me (Y is trans to X). These are initial; preliminary studies that may enable future work establishing these complexes as promising catalysts for related transformations. The catalytic system has interesting key features such as aqueous ethanol media; recyclability; and phosphine-free nature.
Keywords:
Pd-catalysts
Suzuki–Miyaura coupling
aryl halides
phosphine-free
recyclable catalysts
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