Potassium tert-Butoxide: Solubility, Solution Structure, and Reactivity

Fundamental properties including solubility and structure-reactivity correlations of potassium tert-butoxide (KOtBu) are described in this manuscript. A combination of donor solvent titration, diffusion NMR, and DFT studies established that KOtBu exists in one of three solution structures: (1) unsolvated cubic tetramer in non-Lewis basic solvents, (2) disolvated cubic tetramer in Lewis basic solvents, and (3) solvated monomer in protic solvents. These studies dispel the notion that strong aprotic donor solvents lead to deaggregation of KOtBu cubic tetramer. In DMSO, a concentration-dependent equilibrium mixture of bis-DMSO-solvated cubic tetramer, dimsylpotassium, and tert-butanol is formed. Donor solvent association with potassium was contextualized in terms of periodic trends within the alkali metal series. The previously reported 1:1 complex of KOtBu and tert-butanol was found to be highly insoluble and affords poor availability of KOtBu when employed in a model dehydrohalogenation reaction. Reactivity can be recovered by the inclusion of strongly Lewis basic donor solvents that disproportionately stabilize the transition state.