The Formation of Heteroleptic Carbene Homologues by Ligand Exchange— Synthesis of the First Plumbanediyl Dimer

Double bond—yes or no? The centrosymmetic trans-bent dimers 1 and 2 crystallize from a mixture of the corresponding monomeric carbene analogues Rf2Sn/Sn(SiR3)2 or Rf2Sn/Pb(SiR3)2. The question whether the plumbanediyl dimer 2 contains a double bond and therefore becomes the last member of the series of ethene homologues R4E2 (E = Si, Ge, Pb) remains open. R = SiMe3, Rf = 2,4,6-(CF3)3C6H2.