Silk Elliot S, Zhu Haozhe, Shtukenberg Alexander G, Diao Tianning
Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, United States.
ACS Catal. 2025 Jun 17;15(13):11349-11355. doi: 10.1021/acscatal.5c03134. eCollection 2025 Jul 4.
Asymmetric catalysis relies on the design of chiral ligands, but the variety of nitrogen-based ligands remains limited. To address this gap, we have developed a class of -symmetric ,-bidentate ligands, imine-oxazoline (ImOx), derived from amino acids through a four-step synthesis. ImOx features an imine moiety conjugated with a chiral oxazoline ring as a hybrid of α-diimine (ADI) and pyridine oxazoline (PyOx) ligands. Its low symmetry allows for independent optimization at both coordination sites. ImOx improves the enantioselectivity of palladium-catalyzed conjugate addition reactions, demonstrating a strong correlation between ee and the steric effects on both the imine and oxazoline sites. Studies on well-defined organopalladium intermediates reveal that the steric bulk of ImOx necessitates a cationic pathway to promote alkene insertion. Structural characterization of ImOx suggests a stronger -influence compared to PyOx. Moreover, ImOx demonstrates versatile redox activity, promoting the reduction of nickel complexes and stabilizing nickel radical complexes. We anticipate that ImOx will expand the toolkit of chiral N-ligands for asymmetric catalysis.
不对称催化依赖于手性配体的设计，但基于氮的配体种类仍然有限。为了填补这一空白，我们开发了一类通过四步合成从氨基酸衍生而来的不对称、双齿配体——亚胺-恶唑啉（ImOx）。ImOx具有与手性恶唑啉环共轭的亚胺部分，是α-二亚胺（ADI）和吡啶恶唑啉（PyOx）配体的杂化体。其低对称性允许在两个配位位点进行独立优化。ImOx提高了钯催化的共轭加成反应的对映选择性，表明对映体过量（ee）与亚胺和恶唑啉位点上的空间效应之间存在很强的相关性。对明确的有机钯中间体的研究表明，ImOx的空间位阻需要阳离子途径来促进烯烃插入。ImOx的结构表征表明，与PyOx相比，其具有更强的π-影响。此外，ImOx表现出多功能的氧化还原活性，促进镍配合物的还原并稳定镍自由基配合物。我们预计ImOx将扩展用于不对称催化的手性氮配体工具库。
