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

Abstract

In this contribution, three novel diamine pro-ligands, incorporating sterically bulky aryl and aliphatic N-substituents, have been developed; viz. (NCNTCHP)H2 (NCNTCHP = {(TCHP)NCH2}2CH2, TCHP = 2,4,6-tricyclohexylphenyl), (NONTCHP)H2 (NONTCHP = {(TCHP)NSiMe2}2O), and (NONAd)H2 (NONAd = {(Ad)NSiMe2}2O; Ad = 1-adamantyl). Through salt metathesis or transamination synthetic approaches, the N-heterocyclic germylenes, [:Ge(NCNTCHP)], [:Ge(NONTCHP)], and [:Ge(NONAd)], 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(NCNTCHP)] and [:Ge(NONTCHP)], while [:Ge(NONAd)] 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.