Yuji Suzaki, Yuka Kobayashi, Yoshitaka Tsuchido
Apr 1, 2019
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Influential Citations
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Journal
Molecular Catalysis
Abstract
Abstract Sonogashira-coupling of 4-iodoanisole with 4-methylphenylacetylene was conducted in the presence of Pd(II) catalyst, NEt3, CuI and sodium dodecylsulfonate (SDS) in aqueous media. The reaction catalyzed by PdCl2(Me2NCH2CH2NMe2) (2b) at 80 °C affords 4-methoxyphenyl-4′-methylphenylalkyne in 51% yield after 2.0 h, whereas those catalyzed by the complexes with other ethylenediamine derivatives, PdCl2(R2NCH2CH2NR2) (R H, C2H5, C3H7, C4H9, and C6H13), formed the product in lower yields (18–26%). Aqueous solution of complex 2b (5.3 mM) and SDS (168 mM) forms a yellow colloidal solution, which is stable for one night at room temperature. The complexes of ethylenediamines with higher alkyl substituents on the nitrogen atoms do not form apparently homogeneous solutions. TEM (transmission electron micrograph) observation of the former solution ([2b] = 5.3 mM), layered on a copper grid surface, revealed formation of Pd-containing micelles with diameters of ca. 4.0–6.0 nm A mixture of 2b (5.4 mM), 4-iodoanisole (125 mM) and 4-methylphenyl acetylene (250 mM) in water contains micelles with diameters smaller than 40 nm, as is clearly observed by TEM. Mixtures of the other complexes and the substrates contain micelles with larger sizes, and their TEM images are obscure. Thus, complex 2b forms small and clear micelles containing the catalyst and the substrate in the reaction mixture, and the micelle formation enhances the reaction in aqueous media.