The first examples of terminal aluminium and gallium imides bearing heteroatom substituents have been synthesised via the reactions of formally anionic aluminium(I) and gallium(I) precursors with silyl and boryl azides. These systems vary significantly in their lability in solution, with the N(Si i Pr3) and N(Boryl) complexes K[1c] and K[1d] being extremely labile, on account of the strong s-donor capabilities of the trialkylsilyl and boryl substituents and the consequently high basicity at nitrogen. Phenylsilylimido derivatives offer greater stabilization through the p-acceptor capabilities of the SiR3 group. The N(Si t BuPh2) system K[1b] represents a usable compromise between stability and solubility, and has been completely characterized by spectroscopic, analytical and crystallographic methods. All of the systems examined feature minimal p-bonding between the imide ligand and aluminium/gallium, with the HOMO and HOMO-1 orbitals effectively comprising orthogonal lone pairs centred at N.