Constructing a Catalytic Cycle for C–F to C–X (X = O, S, N) Bond Transformation Based on Gold-Mediated Ligand Nucleophilic Attack

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• 作者：Ji-Yun Hu ; Jing Zhang ; Gao-Xiang Wang ; Hao-Ling Sun ; Jun-Long Zhang
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：March 7, 2016
• 年：2016
• 卷：55
• 期：5
• 页码：2274-2283
• 全文大小：611K
• ISSN：1520-510X

文摘

A tricoordinated gold(I) chloride complex, tBuXantphosAuCl, supported by a sterically bulky 9,9-dimethyl-4,5-bis(di-tert-butylphosphino)xanthene ligand (tBuXantphos) was synthesized. This complex features a remarkably longer Au–Cl bond length [2.632(1) Å] than bicoordinated linear gold complexes (2.27–2.30 Å) and tricoordinated XantphosAuCl [2.462(1) Å]. Single-crystal X-ray diffraction analysis of a cocrystal of tBuXantphosAuCl and pentafluoronitrobenzene (PFNB) and UV–vis spectroscopic titration experiments revealed the existence of an anion−π interaction between the Cl anion ligand and PFNB. Stoichiometric reaction between PFNB and tBuXantphosAuOtBu, after replacement of Cl by a more nucleophilic tBuO anion ligand, showed higher reactivity and para selectivity in the transformation of C–F to C–OtBu bond, distinctively different from that when only KOtBu was used (ortho selectivity) under the identical condition. Mechanistic studies including density functional theory calculations suggested a gold-mediated nucleophilic ligand attack of the C–F bond pathway via an S_NAr process. On the basis of these results, using trimethylsilyl derivatives TMS-X (X = OMe, SEt, NEt₂) as the nucleophilic ligand source and the fluorine acceptor, catalytic transformation of the C–F bond of aromatic substrates to the C–X (X = O, S, N) bond was achieved with tBuXantphosAuCl as the catalyst (up to 20 turnover numbers).