Seven-Membered Cyclic Potassium Diamidoalumanyls |
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Authors: | Dr Ryan J Schwamm Prof Michael S Hill Han-Ying Liu Dr Mary F Mahon Dr Claire L McMullin Dr Nasir A Rajabi |
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Institution: | Department of Chemistry, University of Bath Claverton Down, Bath, BA2 7AY UK |
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Abstract: | The seven-membered cyclic potassium alumanyl species, {SiNMes}AlK]2 {SiNMes}={CH2SiMe2N(Mes)}2; Mes=2,4,6-Me3C6H2], which adopts a dimeric structure supported by flanking K-aryl interactions, has been isolated either by direct reduction of the iodide precursor, {SiNMes}AlI], or in a stepwise manner via the intermediate dialumane, {SiNMes}Al]2. Although the intermediate dialumane has not been observed by reduction of a Dipp-substituted analogue (Dipp=2,6-i-Pr2C6H3), partial oxidation of the potassium alumanyl species, {SiNDipp}AlK]2, where {SiNDipp}={CH2SiMe2N(Dipp)}2, provided the extremely encumbered dialumane {SiNDipp}Al]2. {SiNDipp}AlK]2 reacts with toluene by reductive activation of a methyl C(sp3)-H bond to provide the benzyl hydridoaluminate, {SiNDipp}AlH(CH2Ph)]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 {SiNDipp}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, {SiNDipp}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 {SiNDipp}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’ {SiNDipp}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. |
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Keywords: | aluminium coordination modes main group chemistry metal-metal interactions |
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