Unveiling the Anomaly of Reduction of Carborane-bis-silylene-Stabilised Silylone/Germylone Leading to Unusual Oxidation of Si /Ge to Si /Ge with EDA-NOCV Analyses.

Researchers have successfully isolated Si /Ge species, termed silylone and germylone, with two lone pairs of electrons on them. These elusive compounds have been stabilised in singlet ground states by using different donor base ligands. Driess et al. in particular have made strides in this area, isolating carborane-bis-silylene-stabilised silylone/germylone and their N /Pb analogues. Carborane (C B H ) plays a pivotal role as a redox-active ligand, converting from closo-carborane to nido-carborane with the addition of two electrons. Notably, anomalous oxidation of Si /Ge centres in carborane-bis-silylene-stabilised species to Si /Ge has been reported, resulting in the formation of dimeric Si -Si /Ge -Ge di-cationic units. The energy decomposition analysis coupled with natural orbital for chemical valence (EDA-NOCV) study focuses on the carborane-bis-silylene ligand in the free state, and its three other species, including silylone/germylone species. Interestingly, it reveals that the carborane unit in an anionic doublet state tends to form one electron-sharing bond and one dative bond with the counter fragment in its cationic doublet state. This helps us to rationalise why the carborane unit undergoes intramolecular electronic rearrangements leading to the formation of a di-anionic carborane unit with a significantly elongated C-C bond (2.38-2.68 Å) and undergoes unusual oxidation of Si /Ge to Si /Ge .