Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States.
J Am Chem Soc. 2020 Apr 15;142(15):6852-6855. doi: 10.1021/jacs.0c00331. Epub 2020 Apr 1.
Si NMR spectroscopy, the method of continuous variations, and density functional theory computations show that sodium hexamethyldisilazide (NaHMDS) is a disolvated dimer in toluene, a mixture of disolvated dimer and tetrasolvated monomer in THF/toluene, and exclusively monomer in neat THF. The dioxane-solvated NaHMDS only partially deaggregates to monomer even in neat dioxane. N-Si coupling constants and Si chemical shifts show a high and dependable correlation with the aggregation state. Monitoring either chemical shift or coupling constant versus THF concentration even in the high-temperature, rapid-exchange limit affords the solvation numbers consistent with DFT computations. The preparation of N-labeled NaHMDS has been improved.
硅核磁共振波谱、连续变化法和密度泛函理论计算表明，六甲基二硅叠氮化钠（NaHMDS）在甲苯中是溶剂化二聚体，在 THF/甲苯混合物中是溶剂化二聚体和四溶剂化单体的混合物，而在纯 THF 中则是单体。即使在纯二氧六环中，二氧六环溶剂化的 NaHMDS 也只能部分解聚为单体。N-Si 偶合常数和 Si 化学位移与聚集态高度相关且可靠。即使在高温快速交换的极限下，监测化学位移或偶合常数与 THF 浓度的关系也能得到与 DFT 计算一致的溶剂化数。N-标记的 NaHMDS 的制备已得到改进。
