Synthesis, Bonding, and Reduction Chemistry of LBeBrY Complexes (L = Lewis Base, Y = Ar, NR ₂ )

Five base-stabilized beryllium Grignards of the type LBeBrY (L = IDipp (1,3-bis(di iso propylphenyl)imidazol-2-ylidene), I i Pr Me (1,3-di iso propyl-4,5-dimethylimidazol-2-ylidene), CDP Ph (hexaphenylcarbodiphosphorane), Y = Dur (2,3,5,6-tetramethylphenyl = duryl); L = I i Pr Me, Y = Tchp (2,4,6,-tricyclohexylphenyl); L = CAAC Me (1-(2,6-di iso propylphenyl)-2,2,4,4-tetramethylpyrrolydin-5-ylidene, Y = Tmp (2,6-tetramethylpyrrolidine)) were synthesized by salt metathesis from LBeBr 2 or ligand exchange at (Et 2 O)BeBrY. Single-crystal X-ray diffraction analyses show that the angle between the beryllium and carbon ligand planes depends mainly on L, varying from coplanar (L = CDP Ph ) to orthogonal (L = IDipp), via 50–70° for L = I i Pr Me . In contrast, (CAAC Me )BeBrDur and (CAAC Me )BeBrTmp display coplanar and near-orthogonal arrangements, respectively. Energy decomposition analysis in combination with natural orbitals for chemical valence (EDA-NOCV) calculations rationalize these trends as arising from a balance of steric repulsion, stabilizing London dispersion interactions between L and Y, and small but non-negligible BeBrY→L (L = carbene) or L→BeBrY (L = CDP Ph ) π-donation components. Reduction of LBeBrAr led to complex product mixtures, presumably owing to Schlenk-type equilibria as well as the formation of highly reactive [LBeY] · and LBeHY intermediates involved in ligand decomposition reactions. Only the one-electron reduction of (CAAC Me )BeBrTmp afforded a stable linear [(CAAC Me )BeTmp] · radical, which EPR spectroscopy and DFT calculations indicate is a CAAC- rather than a Be-centered radical.