The potassium enolate of tert-butyl methyl ketone reacted with bis (diisopropylamino) boron chloride to give the bis (diisopropylamino) boron enolate of tert-butyl methyl ketone (3b) in 61-84% isolated yields. Unlike the aggregated alkali-metal enolates, this boron enolate exists exclusively as a monomer in both the solid and solution states, as identified by X-ray and diffusion-ordered NMR.