Can Aromatic pi-Clouds Complex Divalent Germanium and Tin Compounds? A DFT Study

The properties of various electron-deficient germylenes and stannylenes are investigated using density functional theory (DFT). The dominant electrophilic character of these divalent group IV compounds is demonstrated by computed DFT-based reactivity descriptors. Next, the interaction of selected model dihalogenated germylenes and stannylenes (GeX2 and SnX2, with X = F, Cl, Br, I) with a series of potential aromatic pi-donors is studied; computed classical donor acceptor sigma-interactions with strong Lewis bases serve as a reference. In addition, natural bond orbital analyses were performed in order to study the interactions at the orbital level, consistently indicating that the most important interaction for the pi-complexations is the overlap of the formal empty p-orbital on the germanium or the tin atom and the pi-orbitals of the aromatic rings. Additional information is obtained from the extent of charge transfer from the pi-donors toward the divalent tin and germanium compounds. The existence of a complexation interaction between the pi-clouds of the aromatic rings and the divalent compounds is theoretically established. The strength of the pi-complexation parallels the trends in electron-donating and electron-withdrawing character of the substituents on the aromatic compounds. Correlations of the total complexation energy with the NBO interaction energy confirm that this pi-complexation is essentially an orbital-controlled interaction. In agreement with experimental data, sigma-complexation is found to dominate over pi-complexation.