Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, Texas 77843, United States.
Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
J Phys Chem Lett. 2021 Jan 14;12(1):13-18. doi: 10.1021/acs.jpclett.0c03216. Epub 2020 Dec 9.
A set of two dodecaborate [B(OR)] radical cluster anions containing a dense layer of fluorinated end-groups provides nuclear spin hyperpolarization via the dissolution dynamic nuclear polarization (D-DNP) technique. We show that these clusters can enhance F nuclear magnetic resonance (NMR) signals. Importantly, given the inherent radical delocalization in dodecaborate-based clusters, these species are compatible with reactive compounds such as Lewis acids, providing ∼1000-2000 times of signal enhancement for B(CF) in liquid state NMR spectroscopy experiments at 9.4 Tesla. This observation suggests that 3D aromatic radicals can provide advantages over the conventional radical species that are currently used for DNP such as 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) by showing superior chemical compatibility. The ability to hyperpolarize reactive compounds using [B(OR)] cluster radicals opens up new applications of reaction monitoring by D-DNP NMR spectroscopy, including the observation of catalytically active species in complex reaction mixtures.
一套由两个十二硼酸盐[B(OR)]自由基簇阴离子组成，其中包含一层密集的氟化端基，通过溶解动态核极化（D-DNP）技术提供核自旋超极化。我们表明，这些簇可以增强 F 核磁共振（NMR）信号。重要的是，鉴于基于十二硼酸盐的簇中自由基的固有离域性，这些物质与路易斯酸等反应性化合物兼容，在 9.4 特斯拉的液体状态 NMR 光谱实验中，B(CF)的信号增强约 1000-2000 倍。这一观察结果表明，3D 芳香族自由基在化学兼容性方面优于目前用于 DNP 的传统自由基，例如 2,2,6,6-四甲基-1-哌啶氧基（TEMPO）。使用[B(OR)]簇自由基极化反应性化合物的能力为通过 D-DNP NMR 光谱进行反应监测开辟了新的应用，包括在复杂反应混合物中观察催化活性物质。
