New monodentate and bidentate silylene ligands by DFT

Considering the importance of silylene ligands in transition metal-mediated catalytic reactions, we have scrutinized eight novel monodentate ( 1 – 4 ) and bidentate ( 1 ^′ - 4 ^′ ) derivatives of 2,5-diX-cyclopentasilylene-2,4-dienes (X = NH₂, OH, PH₂, and SH), at M06/6-311++G** level of theory. To probe the complexation ability of our scrutinized silylene ligands with Rh atom ( 1 _Rh - 4 _Rh and 1 ^′ _Rh - 4 ^′ _Rh , respectively), thermodynamic and structural parameters such as complexation energy (ΔE_Com), singlet-triplet energy gap (ΔE_s-t), bond length, along with NBO and atoms in molecules analyses are provided. In going from less electron donating groups (EDGs) to more EDGs (NH₂ > OH > PH₂ > SH), the σ -donor strength and ligand flexibility increase. Structures 1 and 1 ^′ turn out as the most nucleophilic species for showing the highest nucleophilicity (N = 5.47 and 5.40 eV, respectively). Furthermore, they exhibit the highest proton affinity values (PA = 271.46 and 271.23 kcal/mol, respectively). The results indicate that bidentate coordination mode of silylene leads to a stronger Si-Rh complex. The overall orders of σ -donation ability for monodentate and bidentate silylene ligands are 1 > 2 > 3 > 4 and 1 ^′ > 2 ^′ > 3 ^′ > 4 ^′ , respectively.