Amidines: a deeper look at the archetypal pro-ligand

Amidinates ([R₁NC(R₂)NR₃]^-) are versatile and ubiquitous ligands in inorganic and main group chemistry, due to their anionic, bidentate nature and easy tunability. Herein we present the synthesis of 23 bulky N-aryl substituted aminidinate ligands via three different synthetic routes: 1. condensation reaction in the presence of PPSE (polyphosphric acid trimethylsilylester); 2. the treatment of a carbodiimide with a lithium salt, and 3. the sequential addition of anilines to an acyl chloride and then to the resultant imidoyl chloride. These synthetic routes have been compared and critically analysed. The stabilising properties of the ligands were next probed through complexation with aluminium (AlH₃·NMe₃), where it was found that the bulkier ligands afford aluminium dihydride complexes, whereas the less bulky ligands instead afford bis-ligated aluminium monohydride complexes. Finally, we utilised computational methods to further explore the steric and electronic properties of these ligands, highlighting the differing effects of different substitution patterns.