Curnock Emily, Levason William, Light Mark E, Luthra Sajinder K, McRobbie Graeme, Monzittu Francesco M, Reid Gillian, Williams R Nathan
Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK.
Dalton Trans. 2018 May 1;47(17):6059-6068. doi: 10.1039/c8dt00480c.
Fluorination of [ScCl3(Me3-tacn)] (Me3-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) and [ScCl3(BnMe2-tacn)] (BnMe2-tacn = 1,4-dimethyl-7-benzyl-1,4,7-triazacyclononane) by Cl/F exchange with 3 mol. equiv. of anhydrous [NMe4]F in CH3CN solution yields the corresponding [ScF3(R3-tacn)] (R3 = Me3 or BnMe2). These are the first examples of scandium fluoride complexes containing neutral co-ligands. The fluorination occurs stepwise, and using a deficit of [NMe4]F produced [ScF2Cl(Me3-tacn)]. Attempts to fluorinate [YCl3(Me3-tacn)], [YI3(Me3-tacn)], [LaCl3(Me3-tacn)(OH2)] or [MCl3(terpy)] (M = Sc, Y or La; terpy = 2,2':6'2''-terpyridyl) using a similar method were unsuccessful, due to the Cl/F exchange being accompanied by loss of the neutral ligand from the metal centre. Fluorination of [ScCl3(Me3-tacn)] or [ScCl3(terpy)] with Me3SnF was also successful. The products were identified as the very unusual heterobimetallic [Sc(Me3-tacn)F2(μ-F)SnMe3Cl] and [Sc(terpy)F(μ-F)2(SnMe3Cl)2], in which the Me3SnCl formed in the reaction behaves as a weak Lewis acid towards the scandium fluoride complex, linked by Sc-F-Sn bridges. [Sc(terpy)F(μ-F)2(SnMe3Cl)2] decomposes irreversibly in solution but, whilst multinuclear NMR data show that [Sc(Me3-tacn)F2(μ-F)SnMe3Cl] is dissociated into the [ScF3(Me3-tacn)] and Me3SnCl in CH3CN solution, the bimetallic complex reforms upon evaporation of the solvent. The new scandium fluoride complexes and the chloride precursors have been characterised by microanalysis, IR and multinuclear NMR (1H, 19F, 45Sc) spectroscopy as appropriate. X-ray crystal structures provide unambiguous evidence for the identities of [Sc(Me3-tacn)F2(μ-F)SnMe3Cl], [ScF2Cl(Me3-tacn)], [YI3(Me3-tacn)], [{YI2(Me3-tacn)}2(μ-O)], [ScCl3(terpy)], [YCl3(terpy)(OH2)], and [{La(terpy)(OH2)Cl2}2(μ-Cl)2]. Once formed, the [ScF3(R3-tacn)] complexes are stable in water and unaffected by a ten-fold excess of Cl- or MeCO2-, although they are immediately decomposed by excess F-. The potential use of [ScF3(R3-tacn)] type complexes as platforms for 18F PET (positron emission tomography) radiopharmaceuticals is briefly discussed. Attempts to use the Group 3 fluoride "hydrates", MF3·xH2O, as precursors were unsuccessful; no reaction with R3-tacn or terpy occurred either on reflux in CH3CN or under hydrothermal conditions (H2O, 180° C, 15 h). PXRD data showed that these "hydrates" actually contain the anhydrous metal trifluorides with small amounts of surface or interstitial water.
在乙腈溶液中，通过与3摩尔当量的无水[四甲基铵]氟化物进行氯/氟交换反应，对[三氯化钪（三甲基-1,4,7-三氮杂环壬烷）]（三甲基-1,4,7-三氮杂环壬烷 = 1,4,7-三甲基-1,4,7-三氮杂环壬烷）和[三氯化钪（苄基二甲基-1,4,7-三氮杂环壬烷）]（苄基二甲基-1,4,7-三氮杂环壬烷 = 1,4-二甲基-7-苄基-1,4,7-三氮杂环壬烷）进行氟化，得到相应的[三氟化钪（R3-1,4,7-三氮杂环壬烷）]（R3 = 三甲基或苄基二甲基）。这些是含有中性共配体的氟化钪配合物的首个实例。氟化反应是分步进行的，使用不足量的[四甲基铵]氟化物会生成[二氟化氯钪（三甲基-1,4,7-三氮杂环壬烷）]。尝试使用类似方法对[三氯化钇（三甲基-1,4,7-三氮杂环壬烷）]、[三碘化钇（三甲基-1,4,7-三氮杂环壬烷）]、[三氯化镧（三甲基-1,4,7-三氮杂环壬烷）（水）]或[三氯化M（2,2':6'2''-三联吡啶）]（M = 钪、钇或镧；三联吡啶 = 2,2':6'2''-三联吡啶）进行氟化均未成功，因为氯/氟交换反应伴随着金属中心的中性配体流失。用三甲基氟化锡对[三氯化钪（三甲基-1,4,7-三氮杂环壬烷）]或[三氯化钪（三联吡啶）]进行氟化也取得了成功。产物被鉴定为非常特殊的异双金属[钪（三甲基-1,4,7-三氮杂环壬烷）二氟（μ-氟）三甲基氯化锡]和[钪（三联吡啶）氟（μ-氟）₂（三甲基氯化锡）₂]，其中反应中生成的三甲基氯化锡对氟化钪配合物表现为弱路易斯酸，通过钪 - 氟 - 锡桥相连。[钪（三联吡啶）氟（μ-氟）₂（三甲基氯化锡）₂]在溶液中不可逆分解，但多核核磁共振数据表明，[钪（三甲基-1,4,7-三氮杂环壬烷）二氟（μ-氟）三甲基氯化锡]在乙腈溶液中会解离为[三氟化钪（三甲基-1,4,7-三氮杂环壬烷）]和三甲基氯化锡，不过在溶剂蒸发后双金属配合物会重新形成。新的氟化钪配合物和氯化物前体已通过微量分析、红外光谱和多核核磁共振（¹H、¹⁹F、⁴⁵Sc）光谱进行了适当表征。X射线晶体结构为[钪（三甲基-1,4,7-三氮杂环壬烷）二氟（μ-氟）三甲基氯化锡]、[二氟化氯钪（三甲基-1,4,7-三氮杂环壬烷）]、[三碘化钇（三甲基-1,4,7-三氮杂环壬烷）]、[{二碘化钇（三甲基-1,4,7-三氮杂环壬烷）}₂（μ-氧）]、[三氯化钪（三联吡啶）]、[三氯化钇（三联吡啶）（水）]和[{镧（三联吡啶）（水）二氯}₂（μ-氯）₂]的结构提供了明确证据。一旦形成，[三氟化钪（R3-1,4,7-三氮杂环壬烷）]配合物在水中稳定，不受十倍过量的氯离子或醋酸根离子影响，尽管它们会立即被过量的氟离子分解。简要讨论了[三氟化钪（R3-1,4,7-三氮杂环壬烷）]型配合物作为¹⁸F正电子发射断层扫描（PET）放射性药物平台的潜在用途。尝试使用第3族氟化物“水合物”MF₃·xH₂O作为前体未成功；在乙腈中回流或水热条件（水，180°C，15小时）下，它们与R3-1,4,7-三氮杂环壬烷或三联吡啶均未发生反应。粉末X射线衍射数据表明，这些“水合物”实际上含有无水金属三氟化物以及少量表面水或间隙水。
