由动态核极化增强间接检测到的 195Pt NMR 光谱特征和指纹分析揭示的 N-杂环卡宾配体稳定的 Pt 表面位点的形态和结构,Journal of the American Chemical Society

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由动态核极化增强间接检测到的 195Pt NMR 光谱特征和指纹分析揭示的 N-杂环卡宾配体稳定的 Pt 表面位点的形态和结构
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2022-11-16 , DOI: 10.1021/jacs.2c08300
Zhuoran Wang ₁ , Laura A Völker ₂ , Thomas C Robinson ₁ , Nicolas Kaeffer ₂ , Georges Menzildjian ₁ , Ribal Jabbour ₁ , Amrit Venkatesh _{3,

4} , David Gajan ₁ , Aaron J Rossini _{3,

4} , Christophe Copéret ₂ , Anne Lesage ₁

Affiliation

N-杂环卡宾 (NHC) 是过渡金属催化中广泛使用的配体。值得注意的是，它们越来越多地出现在异构系统中。虽然详细了解可能的多种金属环境对于理解基于金属-NHC 的多相催化剂的活性至关重要，但目前只有少数技术能够描述分散在固体载体上的原子分辨率结构。在这里，我们介绍了一种新的动态核极化 (DNP) 表面增强固态核磁共振 (NMR) 方法，结合先进的密度泛函理论 (DFT) 计算，可以对分离的二氧化硅负载的 Pt-国家卫生健康委网站。尤其，¹³ C- ¹⁹⁵ Pt相关实验。通过利用¹J ( ¹³ C- ¹⁹⁵ Pt) 耦合，获得了 2D NMR 光谱，揭示了两种类型的 Pt 位点。对于它们中的每一个，确定了¹J ( ¹³ C- ¹⁹⁵ Pt) 值以及¹⁹⁵Pt 化学位移张量参数。为了解释 NMR 数据，对广泛的分子 Pt-NHC 复合物库进行了 DFT 计算。虽然一个表面位点被确定为双 NHC 化合物，但第二个位点很可能包含双齿 1,5-环辛二烯配体，表明存在多种平行接枝机制。这里描述的方法代表了催化相关表面金属-NHC 配合物的原子级描述向前迈出了新的一步。特别是，它为利用铂的光谱特征开辟了创新途径，铂是催化中使用最广泛的过渡金属之一，但其在固态 NMR 中的应用仍然很困难。我们的结果还强调了¹⁹⁵ Pt NMR 参数对轻微结构变化的敏感性。

"点击查看英文标题和摘要"

Speciation and Structures in Pt Surface Sites Stabilized by N-Heterocyclic Carbene Ligands Revealed by Dynamic Nuclear Polarization Enhanced Indirectly Detected 195Pt NMR Spectroscopic Signatures and Fingerprint Analysis

N-Heterocyclic carbenes (NHCs) are widely used ligands in transition metal catalysis. Notably, they are increasingly encountered in heterogeneous systems. While a detailed knowledge of the possibly multiple metal environments would be essential to understand the activity of metal-NHC-based heterogeneous catalysts, only a few techniques currently have the ability to describe with atomic-resolution structures dispersed on a solid support. Here, we introduce a new dynamic nuclear polarization (DNP) surface-enhanced solid-state nuclear magnetic resonance (NMR) approach that, in combination with advanced density functional theory (DFT) calculations, allows the structure characterization of isolated silica-supported Pt-NHC sites. Notably, we demonstrate that the signal amplification provided by DNP in combination with fast magic angle spinning enables the implementation of sensitive ¹³C-¹⁹⁵Pt correlation experiments. By exploiting ¹J(¹³C-¹⁹⁵Pt) couplings, 2D NMR spectra were acquired, revealing two types of Pt sites. For each of them, ¹J(¹³C-¹⁹⁵Pt) value was determined as well as ¹⁹⁵Pt chemical shift tensor parameters. To interpret the NMR data, DFT calculations were performed on an extensive library of molecular Pt-NHC complexes. While one surface site was identified as a bis-NHC compound, the second site most likely contains a bidentate 1,5-cyclooctadiene ligand, pointing to various parallel grafting mechanisms. The methodology described here represents a new step forward in the atomic-level description of catalytically relevant surface metal-NHC complexes. In particular, it opens up innovative avenues for exploiting the spectral signature of platinum, one of the most widely used transition metals in catalysis, but whose use for solid-state NMR remains difficult. Our results also highlight the sensitivity of ¹⁹⁵Pt NMR parameters to slight structural changes.

更新日期：2022-11-16

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