Approaching a “Naked” Boryl Anion: Amide Metathesis as a Route to Calcium, Strontium, and Potassium Boryl Complexes

Abstract

Amide metathesis has been used to generate the first structurally characterized boryl complexes of calcium and strontium, {(Me₃ Si)₂ N}M{B(NDippCH)₂ }(thf)_n (M=Ca, n=2; M=Sr, n=3), through the reactions of the corresponding bis(amides), M{N(SiMe₃ )₂ }₂ (thf)₂ , with (thf)₂ Li- {B(NDippCH)₂ }. Most notably, this approach can also be applied to the analogous potassium amide K{N(SiMe₃ )₂ }, leading to the formation of the solvent-free borylpotassium dimer [K{B(NDippCH)₂ }]₂ , which is stable in the solid state at room temperature for extended periods (48 h). A dimeric structure has been determined crystallographically in which the K⁺ cations interact weakly with both the ipso-carbons of the flanking Dipp groups and the boron centres of the diazaborolyl heterocycles, with K⋅⋅⋅B distances of >3.1 Å. These structural features, together with atoms in molecules (QTAIM) calculations imply that the boron-containing fragment closely approaches a limiting description as a "free" boryl anion in the condensed phase.