Seven‐Membered Cyclic Potassium Diamidoalumanyls

The seven‐membered cyclic potassium alumanyl species, [{SiN(Mes)}AlK](2) [{SiN(Mes)}={CH(2)SiMe(2)N(Mes)}(2); Mes=2,4,6‐Me(3)C(6)H(2)], which adopts a dimeric structure supported by flanking K‐aryl interactions, has been isolated either by direct reduction of the iodide precursor, [{SiN(Mes)}AlI], or in a stepwise manner via the intermediate dialumane, [{SiN(Mes)}Al](2). Although the intermediate dialumane has not been observed by reduction of a Dipp‐substituted analogue (Dipp=2,6‐i‐Pr(2)C(6)H(3)), partial oxidation of the potassium alumanyl species, [{SiN(Dipp)}AlK](2), where {SiN(Dipp)}={CH(2)SiMe(2)N(Dipp)}(2), provided the extremely encumbered dialumane [{SiN(Dipp)}Al](2). [{SiN(Dipp)}AlK](2) reacts with toluene by reductive activation of a methyl C(sp (3))‐H bond to provide the benzyl hydridoaluminate, [{SiN(Dipp)}AlH(CH(2)Ph)]K, and as a nucleophile with BPh(3) and RN=C=NR (R=i‐Pr, Cy) to yield the respective Al‐B‐ and Al‐C‐bonded potassium aluminaborate and alumina‐amidinate products. The dimeric structure of [{SiN(Dipp)}AlK](2) can be disrupted by partial or complete sequestration of potassium. Equimolar reactions with 18‐crown‐6 result in the corresponding monomeric potassium alumanyl, [{SiN(Dipp)}Al−K(18‐cr‐6)], which provides a rare example of a direct Al−K contact. In contrast, complete encapsulation of the potassium cation of [{SiN(Dipp)}AlK](2), either by an excess of 18‐cr‐6 or 2,2,2‐cryptand, allows the respective isolation of bright orange charge‐separated species comprising the ‘free’ [{SiN(Dipp)}Al](−) alumanyl anion. Density functional theory (DFT) calculations performed on this moiety indicate HOMO‐LUMO energy gaps in the of order 200–250 kJ mol(−1).