Seven-membered Cyclic Potassium Diamidoalumanyls

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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 . 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. 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 allowsisolation of bright orange charge-separated species comprising the ‘free’ [{SiN Dipp }Al] − alumanyl anion.
Original languageEnglish
JournalChemistry - A European Journal
Early online date17 Aug 2021
DOIs
Publication statusE-pub ahead of print - 17 Aug 2021

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