The mechanism of addition of aldehydes to germene in different solvents: A DFT study

Density functional theory (DFT) with the polarizable continuum model (PCM) for solvation has been used to study the mechanism of the addition of trans-(2-phenylcyclopropyl)carboxaldehyde to dimesitylfluorenylidenegermane. Two different pathways have been observed in the experiment, including [2 + 2] addition and [4 + 2] addition. The reaction is strongly influenced by the choice of solvent: [4 + 2] addition product, 1,2-oxagermin (P1) was the major product in benzene, while [2 + 2] addition product, tetramesityl-1,3-dioxadigermetane and fluorenylidene-(trans-2-phenylcyclopropyl)methane (P2) were the major products in THF. The computations reveal that the different mechanisms are favored in the polar vs. non-polar solvent: [2 + 2] pathway in THF vs. [4 + 2] pathway in benzene.