Tetrazenyl-, Imido-, and Azidoaluminate Derivatives of a Sterically Demanding Bis-Silazide Ligand

The potassium alumanyl [{SiNDipp}AlK]2 (SiNDipp = {CH2SiMe2NDipp}2; Dipp = 2,6-i-Pr2C6H3) reacts with organic azides via reductive N2 elimination. With the less sterically encumbered azides PhN3 and C10H15N3 (1-azidoadamantane), the putative initially formed aluminium imide undergoes facile [2 + 3] cycloaddition to provide the tetrazenylaluminates [{SiNDipp}Al-κ2-N,N′-({N(R)}2N2)]K (R = Ph, C10H15). In contrast, each Al(I) centre of [{SiNDipp}AlK]2 only reacts with a single equivalent of 2,4,6-Me3C6H2N3 to provide the imidoaluminate [{SiNDipp}AlN(2,4,6-Me3C6H2)(K∙C6H6)], which crystallises as a monomer and displays a short Al-N distance of 1.7040(13) Å. Attempts to synthesise the azide [{SiNDipp}AlN3] by reaction of [{SiNDipp}AlI] with an excess of KN3 resulted in exclusive formation of the bis(azido)aluminate [{SiNDipp}Al(N3)2K], which crystallises as an infinite 1-dimensional polymer propagated by μ-(1,3)-N3 bridging interactions between the potassium cations and azide anions. Although the THF-adducted azide [{SiNDipp}AlN3(THF)] may be synthesised and characterised by more stringent control of the reaction stoichiometry, the synthetic viability of this route remains compromised by competitive generation of [{SiNDipp}Al(N3)2K].