The metathesis of carbon–carbon double bonds—the ‘reshuffling’ of their constituting carbene fragments—is a tremendously important preparative tool in industry and academia. Metathesis of heavier alkene homologues is restricted to occasional unproductive examples in phosphorus chemistry and cross-metathesis to mixed heavier alkynes. We now report the thermally induced, transition-metal-free metathesis of purpose-built unsymmetrically substituted digermenes. The A2Ge=GeAB starting materials are thus converted to symmetrically substituted derivatives of the A2Ge=GeA2 and ABGe=GeAB types. The use of tethered auxiliary donors (dimethylaniline groups) in substituents B ensures intramolecular donor–acceptor stabilization of the transient germylene fragments, the intermediacy of which is proven by trapping experiments. Density functional theory calculations shed light on the thermodynamic driving force of the metathesis and validate the crucial role of the tethered donor. With an analogously equipped bridged tetragermadiene precursor (A2Ge=GeB-X-BGe=GeA2), heavier acyclic diene metathesis polymerization occurs, in analogy to the widespread acyclic diene metathesis (ADMET) polymerization in the carbon case, yielding a polydigermene.
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Crystallographic data for the structures in this Article have been deposited at the Cambridge Crystallographic Data Centre under deposition nos. CCDC 1948744 (3b), 1948745 (E-5a), 1948746 (E-5b),1948747 (Z-5b), 1995973 (10) and 1995974 (11). Copies of data can be obtained free of charge from www.ccdc.cam.ac.uk/structures/. All other data supporting the findings of this study are available within the Article and its Supplementary Information.
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We acknowledge Deutsche Forschungsgemeinschschaft (SCHE906/5-1) for funding. We thank B. Oberhausen, T. Klein and G. Kickelbick for assistance with DSC, thermogravimetric analysis and DLS measurements.
The authors declare no competing interests.
Peer review information Nature Chemistry thanks the anonymous reviewers for their contribution to the peer review of this work.
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Supplementary Figs. 1–78, Tables 1–11, Methods and Discussion.
XYZ-files of all DFT-optimized structures
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Klemmer, L., Thömmes, AL., Zimmer, M. et al. Metathesis of Ge=Ge double bonds. Nat. Chem. 13, 373–377 (2021). https://doi.org/10.1038/s41557-021-00639-9