Seven-membered Cyclic Potassium Diamidoalumanyls

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Abstract

The seven-membered cyclic potassium alumanyl species, [{SiN Mes}AlK] 2 [{SiN Mes}={CH 2SiMe 2N(Mes)} 2; Mes=2,4,6-Me 3C 6H 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 2C 6H 3), partial oxidation of the potassium alumanyl species, [{SiN Dipp}AlK] 2, where {SiN Dipp}={CH 2SiMe 2N(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 2Ph)]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.

Original languageEnglish
Pages (from-to)14971-14980
Number of pages10
JournalChemistry - A European Journal
Volume27
Issue number60
Early online date21 Sep 2021
DOIs
Publication statusPublished - 25 Oct 2021

Keywords

  • aluminium
  • coordination modes
  • main group chemistry
  • metal-metal interactions

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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