Isolation of a Diylide-Stabilized Stannylene and Germylene: Enhanced Donor Strength through Coplanar Lone Pair...

The preparation of the first stable diylide-substituted stannylene and germylene (Y₂ E, with E=Ge, Sn and Y=[PPh₃ -C-SO₂ Tol]^- ) is reported. The synthesis is easily accomplished in one step from the sulfonyl-substituted metalated ylide YNa and the corresponding ECl₂ precursors. Y₂ Ge and Y₂ Sn exhibit unusual structures in the solid state and in solution, in which the three adjacent lone pairs in the C-E-C linkage are arranged coplanar to each other. As shown by DFT studies, this bonding situation is preferred over the typical π-donation from the ligands into the empty p-orbital at the metal due to the strong anion-stabilizing ability of the sulfonyl groups in the ylide backbone and their additional coordination to the metal. The alignment of the three lone pairs leads to a remarkable boost of the HOMO energy and thus of the donor strengths of the tetrylenes. Hence, Y₂ Ge and Y₂ Sn become stronger donors than their diamino or diaryl congeners and comparable to cyclic alkyl(amino)carbenes. First reactivity studies confirm the high reactivity of Y₂ Ge and Y₂ Sn, which for example undergo an intramolecular C-H activation reaction via metal-ligand cooperation.