The Lewis Acidity of Bare and Crown Ether‐Complexed Germanium(II) and Tin(II) Cations

The Gutmann-Beckett and Fluoride Ion Affinity methods were used to assess the Lewis acidity of a variety of dicationic germanium(II) and tin(II) crown ether complexes and the corresponding neutral halides. The coordination of two or more equivalents of triethylphosphine oxide (TEPO) was observed which was accompanied by full or partial replacement of the crown ether or chloride ligands from the metal centre illustrating the importance of unambiguously identifying the species in solution to enable a meaningful discussion of relative Lewis acidities. From the coordination complexes observed, the germanium(II) centre was found, in general, to be more Lewis acidic than the tin(II) centre. The crown ether ligands, when retained, had little influence on the Lewis acidity of the complex and may, for ease of synthesis, be used as convenient precursors to "bare" Ge(II) and Sn(II) dicationic catalysts.