Silynes (RC≡SiR') and Disilynes (RSi≡SiR'): Why Are Less Bonds Worth Energetically More?

Bond stabilization through bending! Valence bond analysis shows that the σ frames of 1-3 (1: E = Si, E' = C; 2: E = E' = Si; 3: E = E' = C) are stabilized by trans bending (B), while π bonding is weakened. In acetylene (3) π bonding overrides the σ frame and establishes a linear molecule (3 L). In contrast, the σ frames dominate in silyne (1) and disilyne (2) and lead to trans-bent structures (1 B and 2 B).