N-Heterocyclic germylenes supported by bulky dianionic N,N-chelating ligands

In this contribution, three novel diamine pro-ligands, incorporating sterically bulky aryl and aliphatic N-substituents, have been developed; viz. (NCN^TCHP)H₂ (NCN^TCHP = {(TCHP)NCH₂}₂CH₂, TCHP = 2,4,6-tricyclohexylphenyl), (NON^TCHP)H₂ (NON^TCHP = {(TCHP)NSiMe₂}₂O), and (NON^Ad)H₂ (NON^Ad = {(Ad)NSiMe₂}₂O; Ad = 1-adamantyl). Through salt metathesis or transamination synthetic approaches, the N-heterocyclic germylenes, [:Ge(NCN^TCHP)], [:Ge(NON^TCHP)], and [:Ge(NON^Ad)], have been prepared and crystallographically characterized. The electronic structure of each germylene was studied by DFT calculations. The steric profile of the germanium-bound ligands was also assessed using computational models, and the results compared to those for structurally similar compounds. Significant steric crowding of the germanium centre (>70 % ligand coverage) was observed for [:Ge(NCN^TCHP)] and [:Ge(NON^TCHP)], while [:Ge(NON^Ad)] exhibited substantially less steric saturation at the metal centre (∼62 % ligand coverage). Through these studies, we have shown the potential suitably of the developed ligands to stabilise other low-valent main-group species.