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Stable Actinide π Complexes of a Neutral 1,4-Diborabenzene

Paprocki, Valerie; Hrobárik, Peter; Harriman, Katie L. M.; Luff, Martin S.; Kupfer, Thomas; Kaupp, Martin; Murugesu, Muralee; Braunschweig, Holger

FG Theoretische Chemie - Quantenchemie

The π coordination of arene and anionic heteroarene ligands is a ubiquitous bonding motif in the organometallic chemistry of d-block and f-block elements. By contrast, related π interactions of neutral heteroarenes including neutral bora-π-aromatics are less prevalent particularly for the f-block, due to less effective metal-to-ligand backbonding. In fact, π complexes with neutral heteroarene ligands are essentially unknown for the actinides. We have now overcome these limitations by exploiting the exceptionally strong π donor capabilities of a neutral 1,4-diborabenzene. A series of remarkably robust, π-coordinated thorium(IV) and uranium(IV) half-sandwich complexes were synthesized by simply combining the bora-π-aromatic with ThCl4(dme)2 or UCl4, representing the first examples of actinide complexes with a neutral boracycle as sandwich-type ligand. Experimental and computational studies showed that the strong actinide–heteroarene interactions are predominately electrostatic in nature with distinct ligand-to-metal π donation and without significant π/δ backbonding contributions.