Sodium Hexamethyldisilazide: Using ¹⁵N-²⁹Si Scalar Coupling to Determine Aggregation and Solvation States

²⁹Si 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. ¹⁵N-²⁹Si coupling constants and ²⁹Si 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 ¹⁵N-labeled NaHMDS has been improved.