Redox non-innocent bis-silylene aluminium complexes with a carborane backbone

Abstract

The redox non-innocent bis-silylenyl ortho-carborane ligands [SiII(CCcage)SiII] (CCcage = o-C2B10H10, SiII = ArC(NtBu)2Si; Ar = C6H5, p-tBuC6H4), with their particular chelating and electronic properties, have been employed for the synthesis of new donor-stabilized SiII → AlIII complexes, potential precursors to low oxidation state aluminium complexes. Due to the redox non-innocence of the carborane backbone, [AlI2+] complexes with three ligand oxidation states were characterized: with neutral and radical anionic closo- as well as dianionic nido-C2B10 cores. Reduction at the aluminium center could also be enacted with potassium/naphthalene leading to {K[SiII(CCcage)SiII]Al(C10H8)} derivatives from [1 + 4] cycloaddition reaction. The mechanism of this dearomatization reaction is proposed to occur via the formation of transient low oxidation state aluminium intermediates (radicals and/or aluminylenes) that are trapped by naphthalene.