Stable actinide $\pi$ complexes of a neutral 1,4-diborabenzene

The $\pi$ 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 $\pi$ interactions of neutral heteroarenes including neutral bora-$\pi$-aromatics are less prevalent particularly for the f-block, due to less effective metal-to-ligand backbonding. In fact, $\pi$ complexes with neutral heteroarene ligands are essentially unknown for the actinides. We have now overcome these limitations by exploiting the exceptionally strong $\pi$ donor capabilities of a neutral 1,4-diborabenzene. A series of remarkably robust, $\pi$-coordinated thorium(IV) and uranium(IV) half-sandwich complexes were synthesized by simply combining the bora-$\pi$-aromatic with ThCl${}_4$(dme)${}_2$ or UCl${}_4$, 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 $\pi$ donation and without significant /(/pi//delta/) backbonding contributions. (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH and Co. KGaA.)