An amidinate-stabilized germatrisilacyclobutadiene ylide

The synthesis and characterization of new amidinate-stabilized germatrisilacyclobutadiene ylides [L ₃Si ₃GeL′] (L=PhC(NtBu) ₂; L′=L; =Ge (3), Si (7)) are described. Compound 3 was prepared by the reaction of [LSi-SiL] (1) with one equivalent of [LGe-GeL] (2) in THF. Compound 7 was synthesized by the reaction of 2 with excess 1 in THF. The bisamidinate germylene [L ₂Ge:] (4) is a by-product in both reactions. Moreover, compound 7 was prepared by the reaction of 3 with one equivalent of 1 in THF. Compounds 3 and 7 have been characterized by NMR spectroscopy, X-ray crystallography, and theoretical studies. The results show that compounds 3 and 7 are not antiaromatic. The puckered Si ₃Ge four-membered rings in 3 and 7 have a ylide structure, which is stabilized by amidinate ligands and the electron delocalization within the Si ₃Ge four-membered ring. Heavier cyclobutadiene ylide: The new germatrisilacyclobutadiene ylide 3 was synthesized successfully by the treatment of 1 with 2 (one equiv) in THF (see scheme). The ²⁹Si NMR resonances of compound 3 reveal that the Si ₃Ge four-membered ring has a ylide structure. The X-ray structure of 3 comprises a puckered Si ₃Ge four-membered ring, with the Ge-Si and Si-Si bonds as single bonds. Theoretical studies suggest that the ylide structure in 3 is stabilized by the amidinate ligands and weak electron delocalization.