Bis-Silylene-Supported Aluminium Atoms with Aluminylene and Alane Character

The suitability of electron-rich bis-silylenes, specifically the neutral chelating [Si^II(Xant)Si^II] ligand (Si^II=PhC(N^tBu)₂Si, Xant=9,9-dimethylxanthene) and the anionic [Si^II(N_Acrid)Si^II)]^- pincer ligand (N_Acrid=2,7,9,9-tetramethylacridane), has been successfully probed to stabilize monovalent bis-silylene-supported aluminium complexes (aluminylenes). At first, the unprecedented aluminium(III) iodide precursors [Si^II(Xant)Si^II]AlI₂ ⁺ I^- 1 and [Si^II(N_Acrid)Si^II)]AlI₂ 2 were synthesized using AlI₃ and [Si^II(Xant)Si^II] or [Si^II(N_Acrid)Si^II)]Li(OEt₂)], respectively, and structurally characterized. While reduction of 1 with KC₈ led merely to unidentified products, the dehalogenation of 2 afforded the dimer of the desired {[Si^II(N_Acrid)Si^II)]Al:} aluminylene with a four-membered Si^IV ₂Al^III ₂ ring. Remarkably, the proposed aluminylene intermediates [Si^II(Xant)Si^II]Al^II and {[Si^II(N_Acrid)Si^II)]Al:} could be produced through reaction of 1 and 2 with Collman's reagent, K₂Fe(CO)₄, and trapped as Al^I:→Fe(CO)₄ complexes 5 and 6, respectively. While 6 is stable in solution, 5 loses one CO ligand in solution to afford the silylene- and aluminylene-coordinated iron(0) complex 7 from an intramolecular substitution reaction. The electronic structures of the novel compounds were investigated by Density Functional Theory calculations.