Seven‐Membered Cyclic Potassium Diamidoalumanyls. Issue 60 (21st September 2021)

• Record Type: Journal Article
• Authors: Schwamm, Ryan J.; Hill, Michael S.; Liu, Han‐Ying; Mahon, Mary F.; McMullin, Claire L.; Rajabi, Nasir A.
• Is Part Of: Chemistry. Volume 27:Issue 60(2021)
• Page Start: 14971
• Page End: 14980
• Publication Date: 2021-09-21
• Subjects: aluminium -- coordination modes -- main group chemistry -- metal-metal interactions; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202102682
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The seven‐membered cyclic potassium alumanyl species, [{SiN Mes }AlK]2 [{SiN Mes }={CH2 SiMe2 N(Mes)}2 ; Mes=2, 4, 6‐Me3 C6 H2 ], 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 ‐Pr2 C6 H3 ), partial oxidation of the potassium alumanyl species, [{SiN Dipp }AlK]2, where {SiN Dipp }={CH2 SiMe2 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(CH2 Ph)]K, and as a nucleophile with BPh3 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 . Abstract : Seven‐membered cyclic potassium diamidoalumanyls react with toluene by reductive activation of a methyl C( sp 3 )−H bond and as a nucleophile with BPh3 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 with 18‐cr‐6 or 2, 2, 2‐cryptand to provide either Al−K bonded or charge‐separated species comprising the 'free' alumanyl anion.