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

The suitability of electron‐rich bis‐silylenes, specifically the neutral chelating [SiII(Xant)SiII] ligand (SiII=PhC(NtBu)2Si, Xant=9,9‐dimethylxanthene) and the anionic [SiII(NAcrid)SiII)]− pincer ligand (NAcrid=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 [SiII(Xant)SiII]AlI2+ I− 1 and [SiII(NAcrid)SiII)]AlI2 2 were synthesized using AlI3 and [SiII(Xant)SiII] or [SiII(NAcrid)SiII)]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 {[SiII(NAcrid)SiII)]Al:} aluminylene with a four‐membered SiIV2AlIII2 ring. Remarkably, the proposed aluminylene intermediates [SiII(Xant)SiII]AlII and {[SiII(NAcrid)SiII)]Al:} could be produced through reaction of 1 and 2 with Collman's reagent, K2Fe(CO)4, and trapped as AlI:→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. A transient aluminylene intermediate supported by a pincer bis‐silylene ligand is proposed to form from the reduction of its iodide precursor. It rapidly dimerizes in a [2+2] cycloaddition to give the isolable Si2Al2 heterocycle. In the presence of Fe0, the aluminylene can be stabilized as a dative AlI→Fe0 type complex. The Fe0‐aluminylene complex transforms in solution to foster a silylene‐ and aluminylene‐coordinated Fe0 complex.