M-Ge-Si thermolytic molecular precursors and models for germanium-doped transition metal sites on silica.

The synthesis, thermolysis, and surface organometallic chemistry of thermolytic molecular precursors based on a new germanosilicate ligand platform, -OGe[OSi(O t Bu) 3 ] 3 , is described. Use of this ligand is demonstrated with preparation of complexes containing the first-row transition metals Cr, Mn, and Fe. The thermolysis and grafting behavior of the synthesized complexes, Fe{OGe[OSi(O t Bu) 3 ] 3 } 2 (FeGe), Mn{OGe[OSi(O t Bu) 3 ] 3 } 2 (THF) 2 (MnGe) and Cr{OGe[OSi(O t Bu) 3 ] 3 } 2 (THF) 2 (CrGe), was evaluated using a combination of thermogravimetric analysis; nuclear magnetic resonance (NMR), ultraviolet-visible (UV-Vis), and electron paramagnetic resonance (EPR) spectroscopies; and single-crystal X-ray diffraction (XRD). Grafting of the precursors onto SBA-15 mesoporous silica and subsequent calcination in air led to substantial changes in transition metal coordination environments and oxidation states, the implications of which are discussed in the context of low-coordinate and low oxidation state thermolytic molecular precursors.