Monomeric Two-coordinate Beryllium Imido and Boryloxide Complexes Featuring Be–N and Be–O Triple Bonds

The 2p elements possess a unique propensity to participate in multiple bonding. Realization of multiple bonding involving the 2s elements, however, is challenging and remains exceedingly rare. In this contribution, we present the syntheses, detailed characterization, and molecular structures of heteroleptic beryllium imido and boryloxide complexes of the type [(HCNDip)₂YXBeAr(OEt₂)<i>_n</i>]<i>_m</i> (Y,X = C,N or B,O; <i>n</i> = 0, 1; <i>m</i> = 1, 2; Dip = 2,6-<i>i</i>Pr₂C₆H₃) by salt metathesis and arene elimination approaches. Systematic adjustment of the steric demand of the aryl substituent resulted in the isolation of monomeric, two-coordinate beryllium imido and boryloxide complexes, (HCNDip)₂CNBeTip (<b>9</b>, Tip = 2,4,6-<i>i</i>Pr₃C₆H₂) and (HCNDip)₂BOBeAr^Dip (<b>12</b>, Ar^Dip = 2,6-Dip₂C₆H₃), containing virtually linear C-N-Be-C and B-O-Be-C arrangements and extremely short Be-N (1.434(2) Å, 1.437(3) Å) and Be-O (1.4035(14) Å) bonds, respectively. These were shown by in-depth computational electronic structure and bonding analyses to possess unprecedented triple bond character. The Be-O bond in <b>12</b> constitutes the first s-block metal-oxygen multiple bond.