Now, writing in the Journal of the American Chemical Society, Valentin D. Hannibal and Lutz Greb introduce a strategy to stabilize terminal metalloid oxides by employing a structurally constraining and electron withdrawing symmetric tetra amido macrocyclic ligand (TAML) at germanium (pictured). The TAML ligand (1) readily reacts with tetrakis(dimethylamino)germane in pyridine at 120 °C to form a bis(pyridine) complex (2), which is converted to a pentacoordinate hydroxide anion (3−) with pyridinium (PyH+) as the counterion upon dissolution in water. Reactivity tests, together with density functional theory calculations, reveal enhanced Lewis acidity due to substantial lowest unoccupied molecular orbital (LUMO) lowering induced by the Ge centre deformation towards anti-Van’t-Hoff/Le Bel configuration.
Further deprotonation of 3− salts results in the terminal germanium oxido dianion (42−). The PyH+ salt and strong phosphazene base P4tBu (tBu = tert-butyl) are selected to minimize the countercation interaction and avoid coordinating cations from the base. IR spectroscopy, single-crystal X-ray diffraction, and theoretical studies show a strong, highly ionic Ge–O single bond, stabilized by the central elements’ square planarity, charge delocalization into the TAML backbone, and hydrogen bonding with the methylene groups of TAML.
This is a preview of subscription content, access via your institution
