Inducing Nucleophilic Reactivity at Beryllium with an Aluminyl Ligand
Josef T. Boronski, Lewis R. Thomas‐Hargreaves, Mathias A. Ellwanger, Agamemnon E. Crumpton, Jamie Hicks, Deniz F. Bekiş, Simon Aldridge, Magnus R. Buchner
Abstract
High Resolution Image Download MS PowerPoint Slide The reactions of anionic aluminium or gallium nucleophiles {K[E(NON)]} 2 (E = Al, 1; Ga, 2; NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di tert -butyl-9,9-dimethylxanthene) with beryllocene (BeCp 2 ) led to the displacement of one cyclopentadienyl ligand at beryllium and the formation of compounds containing Be–Al or Be–Ga bonds (NON)EBeCp (E = Al, 3; Ga, 4 ). The Be–Al bond in the beryllium–aluminyl complex [2.310(4) Å] is much shorter than that found in the small number of previous examples [2.368(2) to 2.432(6) Å], and quantum chemical calculations suggest the existence of a non-nuclear attractor (NNA) for the Be–Al interaction. This represents the first example of a NNA for a heteroatomic interaction in an isolated molecular complex. As a result of this unusual electronic structure and the similarity in the Pauling electronegativities of beryllium and aluminium, the charge at the beryllium center (+1.39) in 3 is calculated to be less positive than that of the aluminium center (+1.88). This calculated charge distribution suggests the possibility for nucleophilic behavior at beryllium and correlates with the observed reactivity of the beryllium–aluminyl complex with N,N′ -diisopropylcarbodiimide─the electrophilic carbon center of the carbodiimide undergoes nucleophilic attack by beryllium, thereby yielding a beryllium–diaminocarbene complex.