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

The preparation of the first stable diylide‐substituted stannylene and germylene (Y₂E, with E=Ge, Sn and Y=[PPh₃‐C‐SO₂Tol]⁻) is reported. The synthesis is easily accomplished in one step from the sulfonyl‐substituted metalated ylide YNa and the corresponding ECl₂ precursors. Y₂Ge and Y₂Sn 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, Y₂Ge and Y₂Sn become stronger donors than their diamino or diaryl congeners and comparable to cyclic alkyl(amino)carbenes. First reactivity studies confirm the high reactivity of Y₂Ge and Y₂Sn, which for example undergo an intramolecular C−H activation reaction via metal–ligand cooperation.

Pentafluoroethylated Compounds of Silicon, Germanium and Tin

In this contribution we present an account on pentafluoroethylated compounds of silicon, germanium and tin. The pronounced electron-withdrawing effect of the pentafluoroethyl group leads to a markedly increased Lewis acidity at the central atom which results in the stabilization of hypervalent complexes, anionic element(II) species as well as remarkable reactivities of element-element and element-hydrogen bonds. By addition to unsaturated C-C bonds or by reaction with organic halides as well as transition-metal complexes the molecules bearing a pentafluoroethyl-element group are readily accessible. Moreover, the utilization of pentafluoroethyl groups facilitates the formation of donor-stabilized germylenes and stannylenes. A series of such compounds serves as suitable pentafluoroethylation reagents. Conversely to the well-studied trifluoromethyl derivatives these compounds frequently exhibit a higher thermostability, which allows a more convenient handling.