σ-Type 3-electron-2-center (3e-2c) bonds have been extensively studied as one of the key bonding motifs in radical chemistry and some biological systems. “π-Type 3e-2c-bonded species” that contain a 3e-2c π-bond without an underlying σ-bond framework, however, have been unexplored so far both theoretically and experimentally. Herein, we report the synthesis of the first stable π-type 3e-2c-bonded species, a silicon analogue of a bicyclo[1.1.0]butane radical anion. This compound exhibits an extremely long bridgehead Si−Si bond (3.0638(8) Å) and a strong near-IR absorption at 922 nm in solution which arises from a HOMO→SOMO [π(Si−Si)→π*(Si−Si)] transition. DFT calculations revealed a π-type bonding interaction between the two bridgehead silicon atoms with an unpaired electron mainly delocalized across the corresponding π*-type orbital, which introduces a novel bonding motif for constructing π-electron systems.
|Journal||Angewandte Chemie - International Edition|
|Publication status||Published - 2022 May 9|
- 3e-2c Bonds
- Main Group Elements
- Radical Ions
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