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.
We report on the synthesis of N-heterocyclic tetrylenes ligated by the NON-donor framework 4,5-bis(2,6-diisopropylphenylamino)-2,7-di-tert-butyl-9,9-dimethylxanthene. The molecular structures of the germylene (3), stannylene (4) and plumbylene (5) where determined by X-ray diffraction studies. Furthermore, we present quantum chemical studies on the σ-donor and πacceptor properties of 3-5. Additionally, we report on the reactivity of the tetrylenes towards the transition metal carbonyls [Rh(CO) 2 Cl] 2 , [W(CO) 6 ] and [Ni(CO) 4 ]. The isolated complexes (6 and 7) show the differing reactivity of NHTs compared to NHCs. Instead of just forming the anticipated complex [(NON) SnÀ Rh(CO) 2 Cl], 4 inserts into the RhÀ Cl bond to afford [(NON) Sn(Cl)Rh(CO)(C 6 H 6 )] (6, additional CO/C 6 H 6 exchange) and [(NON)Sn(Cl)Rh 2 (CO) 4 Cl] (7). By avoiding halogenated transition metal precursors in order to prevent insertion reactions, germylene 3 shows "classical" coordination chemistry towards {Ni(CO) 3 } forming the complex [(NON)GeÀ Ni(CO) 3 ] (8).
Die π‐Koordination von Aren‐ und anionischen Heteroarenliganden ist ein allgegenwärtiges Strukturmotiv in der metallorganischen Chemie der d‐ und f‐Block‐Elemente. Im Gegensatz dazu sind vergleichbare π‐Wechselwirkungen neutraler Heteroarene, darunter auch solche neutraler, aromatischer Borheterocyclen, für den f‐Block weit weniger verbreitet, was z. T. mit einer geringeren Effektivität der Metall‐zu‐Ligand‐Rückbindung in Zusammenhang gebracht werden kann. Für die Actinoide sind π‐Komplexe mit neutralen Heteroarenliganden sogar gänzlich unbekannt. Durch Ausnutzung der außergewöhnlichen π‐Donorstärke eines 1,4‐Diborabenzols ist es uns nun gelungen, eine Reihe stabiler π‐Halbsandwichkomplexe des Thoriums(IV) und des Urans(IV) über einen erstaunlich einfachen Zugang zu generieren: Umsetzung eines 1,4‐Diborabenzols mit ThCl4(dme)2 bzw. UCl4 in Gegenwart einer Lewis‐Base. Hierdurch konnten die ersten Beispiele für Actinoidkomplexe mit einem neutralen Borheterocyclus als Sandwich‐artigem Liganden erhalten werden. Laut experimentellen und theoretischen Studien ist die starke Actinoid‐Heteroaren‐Wechselwirkung in diesen Molekülen im Wesentlichen von elektrostatischer Natur. Der kovalente Hauptbeitrag wird hingegen von der Ligand‐zu‐Metall‐π‐Wechselwirkung geleistet, während π/δ‐Rückbindungsanteile kaum eine Rolle spielen.
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