Aluminium and Gallium Silylimides as Nitride Sources

Terminal aluminium and gallium imides of the type K[(NON)M(NR)], bearing heteroatom substituents at R, have been synthesised via reactions of anionic aluminium(I) and gallium(I) reagents with silyl and boryl azides (NON=4,5‐bis(2,6‐diisopropyl‐anilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethyl‐xanthene). These systems vary significantly in their lability in solution: the N(SiiPr3) and N(Boryl) complexes are very labile, on account of the high basicity at nitrogen. Phenylsilylimido derivatives provide greater stabilization through the π‐acceptor capabilities of the SiR3 group. K[(NON)AlN(SitBuPh2)] offers a workable compromise between stability and solubility, and has been completely characterized by spectroscopic, analytical and crystallographic methods. The silylimide species examined feature minimal π‐bonding between the imide ligand and aluminium/gallium, with the HOMO and HOMO‐1 orbitals effectively comprising orthogonal lone pairs centred at N. Reactivity‐wise, both aluminium and gallium silylimides can act as viable sources of nitride, [N]3−, with systems derived from either metal reacting with CO to afford cyanide complexes. By contrast, only the gallium system K[(NON)Ga{N(SiPh3)}] is capable of effecting a similar transformation with N2O to yield azide, N3−, via formal oxide/nitride metathesis. The aluminium systems instead generate RN3 via transfer of the imide fragment [RN]2−. Terminal aluminium and gallium silylimides have been accessed for the first time by exploiting the oxidative reactions of anionic aluminium(I)/gallium(I) (‘aluminyl’/’gallyl’) reagent with silylazides. These compounds feature minimal M=N π‐bonding and can be shown to act as sources of the nitride ion, [N]3− in reactions with CO or N2O.