Silicon-containing formal 4π-electron four-membered ring systems: Antiaromatic, aromatic, or nonaromatic?

Yun Fang Yang, Gui Juan Cheng, Jun Zhu, Xinhao Zhang, Shigeyoshi Inoue, Yun Dong Wu

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


Density functional theory calculations (B3LYP) have been carried out to investigate the 4π-electron systems of 2,4-disila-1,3-diphosphacyclobutadiene (compound 1) and the tetrasilacyclobutadiene dication (compound 2). The calculated nucleus-independent chemical shift (NICS) values for these two compounds are negative, which indicates that the core rings of compounds 1 and 2 have a certain amount of aromaticity. However, deep electronic analysis reveals that neither of these two formal 4π-electron four-membered ring systems is aromatic. Compound 1 has very weak, almost negligible antiaromaticity, and the amidinate ligands attached to the Si atoms play an important role in stabilizing this conjugated 4π-electron system. The monoanionic bidentate ligand interacts with the conjugated π system to cause π-orbital splitting. This ligand-induced π-orbital splitting effect provides an opportunity to manipulate the gap between occupied and unoccupied π orbitals in conjugated systems. Conversely, compound 2 is nonaromatic because its core ring does not have a conjugated π ring system and does not fulfill the requirements of a Hückel system.

Original languageEnglish
Pages (from-to)7516-7524
Number of pages9
JournalChemistry - A European Journal
Issue number24
StatePublished - 11 Jun 2012
Externally publishedYes


  • aromaticity
  • conjugation
  • density functional calculations
  • molecular orbital analysis
  • silicon


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