Seven‐Membered Cyclic Potassium Diamidoalumanyls
Ryan J. Schwamm, Michael S. Hill, Han‐Ying Liu, Mary F. Mahon, Claire L. McMullin, Nasir A. Rajabi
Abstract
Abstract 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 .