Germanium Complexes with O N O Tridentate Ligands: O-H Bond Activation Control According to DFT Calculations.

Polydentate ligands are used for thermodynamic stabilization of tetrylenes-low-valent derivatives of Group 14 elements (E = Si, Ge, Sn, Pb). This work shows by DFT calculations how the structure (the presence or absence of substituents) and type (alcoholic, Alk, or phenolic, Ar) of tridentate ligands 2,6-pyridinobis(1,2-ethanols) [ Alk ONO R ]H 2 and 2,6-pyridinobis(1,2-phenols) [ Ar ONO R ]H 2 (R = H, Me) may affect the reactivity or stabilization of tetrylene, indicating the unprecedented behavior of Main Group elements. This enables the unique control of the type of the occurring reaction. We found that unhindered [ ONO H ]H 2 ligands predominantly led to hypercoordinated bis -liganded {[ ONO H ]} 2 Ge complexes, where an E(+2) intermediate was inserted into the ArO-H bond with subsequent H 2 evolution. In contrast, substituted [ ONO Me ]H 2 ligands gave [ ONO Me ]Ge: germylenes, which may be regarded as kinetic stabilized products; their transformation into E(+4) species is also thermodynamically favorable. The latter reaction is more probable for phenolic [ Ar ONO ]H 2 ligands than for alcoholic [ Alk ONO ]H 2 . The thermodynamics and possible intermediates of the reactions were also investigated.