Tridentate Ligand with Three Carbanions as Donor Atoms: Formation of Dinuclear, Heptacyclic Complexes of Boron, Aluminum, or Gallium with B-C-B, Al-C-Al, or Ga-C-Ga Three-Center-Two-Electron Bonds.

The trilithium compound 1,3-[PhMeSi-C(Li)═C(H)]CHLi () reacted with BCl, AlCl, or GaCl by salt elimination to yield dinuclear heptacyclic compounds (). Two tridentate tricarbanionic ligands coordinate two B, Al, or Ga atoms and adopt a helical arrangement of the ligands around a central E unit. The unusual structures comprise EC heterocycles with two 3c-2e (three-center-two-electron) E-C-E bonds and two C atoms of aromatic rings in the bridging positions. While such a bonding situation is well-documented in Al chemistry, it is rare for B and Ga compounds. Insight into the bonding situation of the molecules is provided by DFT calculations.