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

Reaction of the imidazolium-substituted iphosphate-diide, (Ipr) 2 C 2 P 2 (IDP), with GeCl 2  ⋅ dioxane and KBArF 24 [(BarF 24 ) - =tetrakis[(3,5-trifluoromethyl)phenyl]borate)] afforded the dicationic spherical-aromatic nido-cluster [Ge(η 4 -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(η 4 -C 4 H 4 )]. [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 AgSbF 6 . 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.