Ionic liquids with aprotic heterocyclic anions (AHAs) have been developed for postcombustion CO₂ capture applications. The anions of AHA ILs play a significant role in tuning anion–CO₂ complexation. In addition, AHAs are able to trigger the abstraction of acidic protons located at the α position of phosphonium cations by forming hydrogen bonds between cations and anions, eventually leading to cation-driven CO₂ complexation. Here we investigate the role of the anion in cation–anion hydrogen bonding and ylide formation. Using CO₂ uptake measurements, ³¹P nuclear magnetic resonance (NMR), attenuated total reflection-Fourier transform infrared (ATR-FTIR) deuterium exchange equilibrium and rates, two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY), and density functional theory calculations, we show that the key is the proximity of the negatively charged nitrogen atoms on the anion to the α protons, which is governed not just by anion basicity but by sterics. Thus, we show that triethyl(octyl)phosphonium 3-methyl-5-trifluoromethylpyrazolide is much more effective in hydrogen-bonding with and deprotonating the cation than the equivalent [P₂₂₂₈] ILs with more basic 2-cyanopyrrolide and 3-trifluoromethylpyrazolide anions.

中文翻译：

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三乙基（辛基）phosph离子液体中的阳离子-阴离子和阴离子-CO2与非质子杂环阴离子（AHA）的相互作用。

具有质子惰性杂环阴离子（AHA）的离子液体已被开发用于燃烧后的CO ₂捕集应用。AHA ILs的阴离子在调节阴离子-CO ₂络合中起重要作用。另外，AHA能够通过在阳离子和阴离子之间形成氢键来触发位于phospho阳离子α位的酸性质子的提取，最终导致阳离子驱动的CO ₂络合。在这里，我们研究了阴离子在阳离子-阴离子氢键和内鎓盐形成中的作用。使用CO ₂吸收测量，³¹P核磁共振（NMR），衰减全反射-傅立叶变换红外（ATR-FTIR）氘交换平衡和速率，二维核Overhauser效应光谱（2D NOESY）以及密度泛函理论计算，我们发现关键在于阴离子上带负电荷的氮原子与α质子的接近程度，这不仅取决于阴离子的碱性，还取决于空间的空间。因此，我们显示，与具有更多碱性2-氰基吡咯化物和3-三氟甲基吡唑化物阴离子的等价[P ₂₂₂₈ ] IL相比，三乙基（辛基）phosph 3-甲基-5-三氟甲基吡唑化物与阳离子进行氢键结合和去质子化更为有效。