دانلود رایگان مقاله لاتین هوموکوپلینگ انتخابی اسید فنیل از سایت الزویر
عنوان فارسی مقاله:
هوموکوپلینگ انتخابی اسید فنیل بر نانوذرات پالادیم حمایت شده در حلال biphase
عنوان انگلیسی مقاله:
Selective homocoupling of phenylboronic acid over supported Pd nanoparticle in biphase solvent
سال انتشار : 2017
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مقدمه انگلیسی مقاله:
1. Introduction
One of the most important developments in the field of organic synthesis is the metal-catalyzed coupling reactions, which are widely used for the formation of C\\C bonds [1–12]. The well-known coupling reactions (e.g. Suzuki [1,13–15], Heck [16–18] and Sonogashira reactions [18–20]) have attracted much attention in both laboratory research and industrial application. Conventionally, homogeneous Pd complex is employed as highly active catalyst for the coupling reactions [2,5, 20]. Notably, these homogeneous catalysts have difficulty in separation and regeneration from the reaction liquor, which makes it high-cost and environmentally unfriendly for wide applications [21]. Supporting Pd nanoparticles or complex on the solid support to synthesize heterogeneous catalyst is regarded as efficient method to solve the problem in catalyst separation [22,23,24]. However, in most of these cases, the soluble organic ligands are still necessary, making these processes are still unsatisfactory for further application. Therefore, developing efficient heterogeneous catalysts without using organic ligands is still challenging. The aerobic homocoupling of phenylboronic acid has been regarded as an efficient strategy to synthesize biphenyl without using toxic halogen aromatics [25]. However, phenol by-product is usually formed in the homocoupling reactions, where the yield of desired biphenyl product is still unsatisfactory. Hindering the formation of phenol to improve the biphenyl selectivity in homocoupling is an attractive topic, but achieving this goal is difficult due to the easy formation of phenol from the coupling of aromatic intermediate and hydroxyl species. Additionally, it is worth noting that Au-based catalysts of Au+-Shiff based complex [26], Au nanoparticles [25,27], and CeO2 supported Au3+ and Au+ species [28] have been found to be efficient catalysts for the homocoupling of phenylboronic acid. To the best of our knowledge, Pd nanoparticle catalysts, which have been industrially used for various reactions, are more beneficial for wide application than Au catalysts, but the Pd nanoparticles also have the problems in biphenyl selectivity. Therefore, developing efficient Pd catalysts for the homocoupling of phenylboronic acid with high selectivity to biphenyl is challenging. In this work, we reported an effective strategy to improve the biphenyl selectivity by employing a biphasic solvent of water-toluene mixture over hydrophilic Pd catalyst. In this case, the coupling reactions occurred in water, and the biphenyl product formed in water could be immediately extracted into the toluene, leading to the shift of reaction balance to the formation of biphenyl. By using a hydrophilic mesoporous silica supported Pd catalyst, which has been widely studied in various reactions [29–32], the conversion of phenylboronic acid and selectivity of biphenyl could reach as high as 99.0 and 83.0%, respectively, which are much higher than those in mono-phase solvent under the same reaction conditions. More importantly, the heterogeneous Pd catalysts in the biphase solvent can be easily separated, exhibiting excellent recyclability in the aerobic homocoupling reactions.
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کلمات کلیدی:
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