Silver- and Acid-Free Catalysis by Polyoxometalate-Assisted Phosphanegold(I) Species for Hydration of Diphenylacetylene

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• 作者：Hidekazu Arai ; Takuya Yoshida ; Eri Nagashima ; Akifumi Hatayama ; Shogo Horie ; Satoshi Matsunaga ; Kenji Nomiya
• 刊名：Organometallics
• 出版年：2016
• 出版时间：June 13, 2016
• 年：2016
• 卷：35
• 期：11
• 页码：1658-1666
• 全文大小：383K
• 年卷期：0
• ISSN：1520-6041

文摘

A DMSO-soluble intercluster compound consisting of a tetra{phosphanegold(I)}oxonium cation and an α-Keggin polyoxometalate (POM) anion, [{Au(PPh₃)}₄(μ₄-O)]₃[α-PW₁₂O₄₀]₂ (1), was found to be an effective precatalyst for the silver- and acid-free catalysis of diphenylacetylene hydration (0.67 mol % catalyst; conversions 36.1%, 55.2%, and 93.7% after 4, 6, and 24 h reactions, respectively). The reaction proceeded in the suspended system in 6 mL of 1,4-dioxane/water (4:1) at 80 °C because of the low solubility of 1. Similar POM-based phosphanegold(I) compounds [{{Au(PPh₃)}₄(μ₄-O)}{{Au(PPh₃)}₃(μ₃-O)}][α-PW₁₂O₄₀]·EtOH (5), which is composed of a heptakis{triphenylphosphanegold(I)}dioxonium cation and an α-Keggin POM anion, and [Au(CH₃CN)(PPh₃)]₃[α-PMo₁₂O₄₀] (6), which consists of an acid-free monomeric phosphanegold(I) acetonitrile cation and an α-Keggin molybdo-POM anion, also exhibited acid-free catalysis for the hydration of diphenylacetylene. An induction period was observed in the catalysis by 5. On the other hand, their component species, or phosphanegold(I) species without the POM anion, such as [{Au(PPh₃)}₄(μ₄-O)](BF₄)₂ (2) and [{Au(PPh₃)}₃(μ₃-O)]BF₄ (3), and the monomeric phosphanegold(I) complex [Au(RS-pyrrld)(PPh₃)] (4) (RS-Hpyrrld = RS-2-pyrrolidone-5-carboxylic acid), the last of which has been used as a precursor for the preparation of 1, 5, and 6, showed poor activities in this reaction (0.67 mol % catalysts; conversions 1.8%, 1.7%, and 0.5% after 24 h reactions, respectively). However, upon adding the free-acid form of Keggin POM, i.e., H₃[α-PW₁₂O₄₀]·7H₂O (H-POM: 0.67 mol %), 2–4 exhibited remarkably enhanced activities (conversion 97.6% each after 24 h reactions). In contrast, the activities were not enhanced after adding either the sodium salt of the Keggin POM, Na₃[α-PW₁₂O₄₀]·8H₂O (Na-POM; 0.67 mol %), or a Brønsted acid 10% HBF₄ aqueous solution (0.67 mol %). Both H-POM and Na-POM themselves exhibited no activity. Catalysis by the phosphanegold(I) species for diphenylacetylene hydration was influenced significantly under the free-acid form or sodium salt of the Keggin POM. Acid-free catalytic hydration by 1 of other alkynes, such as phenylacetylene and 1-phenyl-1-butyne, was also examined.