Synthesis and structural characterization of the bis(diisopropylamino)boron enolate of tert-butyl methyl ketone

Article abstract of DOI:10.1021/om700676w

Lithium, sodium, and potassium enolates reacted with bisaminoboron halides to give bisaminoboron enolates 1a-5c. Specifically, the potassium enolate of tert-butyl methyl ketone reacted with bis-(diisopropylamino)boron chloride in THF at room temperature within 1h to give the bis(diisopropylamino)-boron enolate of tert-butyl methyl ketone (3b) in 61-84% isolated yields. Under similar conditions, the reactivity is highly dependent on the metal employed to generate enolates (K > Na > Li) as well as the nitrogen substituents in the bisaminoboron halides (iPr > Et > TMS). This latter observation is a compromise between the boron-nitrogen resonance and the steric effect. The structural information of enolate 3b was studied in detail. 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.