Ligand Binding Constants to Lithium Hexamethyldisilazide Determined by Diffusion-Ordered NMR Spectroscopy

We report the direct measurement of ligand-binding constants of organolithium complexes using a 1H NMR/diffusion-ordered NMR spectroscopy (DOSY) titration technique. Lithium hexamethyldisilazide complexes with ethereal and ester donor ligands (THF, diethyl ether, MTBE, THP, tert-butyl acetate) are characterized using 1H NMR and X-ray crystallography. Their aggregation and solvation states are confirmed using diffusion coefficient–formula weight correlation analysis, and the 1H NMR/DOSY titration technique is applied to obtain their binding constants. Our work suggests that steric hindrance of ethereal ligands plays an important role in the aggregation, solvation, and reactivity of these complexes. It is noteworthy that diffusion methodology is utilized to obtain binding constants.本研究报道了采用氢核磁共振波谱/扩散序谱核磁共振波谱（diffusion-ordered NMR spectroscopy, DOSY）滴定技术直接测定有机锂配合物配体结合常数的工作。以六甲基二硅氮锂与醚类、酯类给体配体（四氢呋喃（tetrahydrofuran, THF）、乙醚、甲基叔丁基醚（methyl tert-butyl ether, MTBE）、四氢吡喃（tetrahydropyran, THP）、乙酸叔丁酯）形成的配合物为研究对象，通过氢核磁共振波谱与X射线晶体衍射法对其进行表征。通过扩散系数-式量相关性分析确认了该类配合物的聚集态与溶剂化状态，并利用氢核磁共振/DOSY滴定技术获取了其配体结合常数。本研究表明，醚类配体的位阻效应在这类配合物的聚集、溶剂化及反应活性中发挥着重要作用。值得注意的是，本研究通过扩散谱方法直接获取配体结合常数。