A Germapyramidane Switches Between 3D Cluster and 2D Cyclic Structures in Single-Electron Steps

Reaction of the imidazolium-substituted iphosphate-diide, (Ipr)₂ C₂ P₂ (IDP), with GeCl₂  ⋅ dioxane and KBArF₂₄ [(BarF₂₄ )^- =tetrakis[(3,5-trifluoromethyl)phenyl]borate)] afforded the dicationic spherical-aromatic nido-cluster [Ge(η⁴ -IDP)]²⁺ ([1]²⁺ ) (Ipr=1,3-bis(2,6-diisopropylphenyl)imidazolium-2-ylidene). This complex is a rare heavy analogue of the elusive pyramidane [C(η⁴ -C₄ H₄ )]. [1]²⁺ undergoes two reversible one-electron reductions, which yield the radical cation [2]⋅⁺ and the neutral Ge^II species 3. Both [2]⋅⁺ and 3 rearrange in solution forming the 2D aromatic and planar imidazolium-substituted digermolide [4]²⁺ and germole-diide 5, respectively. Both planar species can be oxidized back to [1]²⁺ using AgSbF₆ . These redox-isomerizations correspond to the fundamental transformation of a 3D aromatic cluster into a 2D aromatic ring compound upon reduction and vice versa. The mechanism of these reactions was elucidated using DFT calculations and cyclic voltammetry experiments.