New N - heterocyclic mono - and disilavinylidene iron - complexes by density functional theory

Recently, we found less nucleophilicity (N) for normally and abnormally disubstituted Arduengo-type monosilylenes [R2N4Si:] (1-10) than their corresponding disilavinylidene ligands [R2N4Si(sic)Si:] (1 '-10 '). Considering the importance of silylene-iron complexes, here we compare and contrast thermodynamic properties of their novel [R2N4Si: -> Fe(N(SiH3)(2))(2)] (1(c)-10(c)) and [R2N4Si(sic)Si: -> Fe(N(SiH3)(2))(2)] iron complexes (1 '(c)-10 '(c)), for R = H, Me, ethyl, i-propyl, and t-butyl, at B3LYP/6-311++G**+ LANL2DZ level of theory. Isodesmic reactions show higher stability for disilavinylidenes 1 '(c)-10 '(c) compared with their corresponding monosilylene 1(c)-10(c). In all species, the natural bond orbital (NBO) calculations show transfer of charge from the silylene (of the ligand) to iron(II). Multiple Fe-Si bonding character is detected in all complexes (Wiberg bond index > 1). Yet Fe-Si bond distances in 1 '(c)-10 '(c) appear shorter than those in their corresponding 1(c)-10(c). Binding energy (Delta E-bin) of [Fe(N(SiH3)(2))(2)] with 1 '-10 ' appears higher in 1 '(c)-10 '(c) than the corresponding 1(c)-10(c).