Seven-Membered Cyclic Potassium Diamidoalumanyls.

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(sp³ )-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 .

SUBMITTER: Schwamm RJ 

PROVIDER: S-EPMC8596455 | biostudies-literature | 2021 Oct

REPOSITORIES: biostudies-literature