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

摘要

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 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 pi donation and without significant pi/delta backbonding contributions.