N-Triflylphosphoramides (NTPAs) represent an important catalyst class in asymmetric catalysis due to their multiple hydrogen bond acceptor sites and acidity, which is increased by several orders of magnitude compared to conventional chiral phosphoric acids (CPAs). Thus, NTPAs allow for several challenging transformations, which are not accessible with CPAs. However, detailed evidence on their hydrogen bonding situation, complex structures and aggregation is still lacking. Therefore, this study covers the hydrogen bonding behavior and structural features of binary NTPA/imine complexes compared to their CPA counterparts. Deviating from the single-well potential hydrogen bonds commonly observed in CPA/imine complexes, the NTPA/imine complexes exhibit a tautomeric equilibrium between two proton positions. Low-temperature NMR at 180 K supported by computer simulations indicates a OHN hydrogen bond between the phosphoramide oxygen and the imine, instead of the mostly proposed NHN H-bond. Furthermore, this study finds no evidence for the existence of dimeric NTPA/NTPA/imine complexes as previously suggested for CPA systems, both synthetically and through NMR studies.

中文翻译：

---

高酸性 N-三氟甲基磷酰胺作为手性布朗斯台德酸催化剂：弱氢键和多个受体对复杂结构和聚集的影响


N-三氟甲磷酰胺（NTPA）由于其多个氢键受体位点和酸性而成为不对称催化中重要的催化剂类别，与传统的手性磷酸（CPA）相比，酸性增加了几个数量级。因此，NTPA 允许进行一些具有挑战性的转变，而 CPA 无法实现这些转变。然而，关于它们的氢键情况、复杂结构和聚集的详细证据仍然缺乏。因此，本研究涵盖了二元 NTPA/亚胺复合物与其 CPA 对应物相比的氢键行为和结构特征。与 CPA/亚胺复合物中常见的单井潜在氢键不同，NTPA/亚胺复合物在两个质子位置之间表现出互变异构平衡。计算机模拟支持的 180 K 低温 NMR 表明磷酰胺氧和亚胺之间存在 OHN 氢键，而不是大多数提出的 NHN H 键。此外，本研究没有发现任何证据表明二聚体 NTPA/NTPA/亚胺复合物的存在，正如之前对 CPA 系统所建议的那样，无论是合成还是通过 NMR 研究。