Surface Organometallic Chemistry of Germanium: Evidence for the Formation of Highly Thermally Stable ≡Si—O—GeR₃ Fragments by Reaction of GeR₄ Complexes (R = n-Bu, Et) with the Surface of Silica

Interaction between GeR₄ complexes with partially dehydroxylated silica surfaces has been studied by infrared spectroscopy, ¹³C CP-MAS NMR, and analytical methods. The tetraalkylgermanium complexes are physisorbed, at room temperature: a hydrogen-type bonding occurs between the terminal methyl group of the alkyl ligands and the surface silanol groups. The results obtained for the two complexes (R = Et, n-Bu) and for two supports (silica₂₀₀) and silica(₅₀₀)) are rather similar and may be explained by a simple reaction between the surface silanols and the tetraalkylgermanium compounds: ≡Si—O—H + GeR₄ →≡Si—O—GeR₃ + RH. Surprisingly, thermal treatment under vacuum (10⁻⁴ Torr) of the well-defined ≡Si—O—GeR₃ complex supported on silica(₂₀₀) and silica(₅₀₀) does not lead to any evolution of gas between 200 and 400 °C. The stabilility of the grafted complex is also evidenced by analytical data and by infrared spectroscopy. The extraordinary thermal stability of ≡Si—O—GeR₃ is compatible with the higher stability of germanium alkyl complexes as compared with the tin ones. A mechanism of decomposition of the surface alkyl complexes is proposed.