Potassium Isopropyl(trimethylsilyl)amide and Potassium tert-Butyl(trimethylsilyl)amide: Solvent-Dependent Solution Structures and Reactivities

Potassium isopropyl(trimethylsilyl)amide (KPTA) and potassium tertbutyl(trimethylsilyl)amide (KBTA) were prepared as stable 1.0 M stock solutions in Et3N or isolable crystalline solids. A combination of the Method of Continuous Variations and a heavy reliance on 29Si NMR spectroscopy revealed solventdependent dimers and monomers. DFT computations offered insights into the solvation. Weakly coordinating solvents such as toluene and triethylamine afford dimers. In THF, KPTA is dimeric whereas KBTA is dimeric at low THF concentration and monomeric in neat THF. Chronic and often poorly understood loss of the 29Si resonance made a broadly based, systematic study difficult and may have obscured deaggregation or ionization. Reactivity was probed using orthometalations by KBTA, which pressed the limits of its basicity and probably impacted the yields in some cases.