Germanium Complexes with O(N)under-barO 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) [O-Alk (N) under barO(R)]H-2 and 2,6-pyridinobis(1,2-phenols) [O-Ar (N) under bar OR]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 [O (N) under barO(H)]H-2 ligands predominantly led to hypercoordinated bis-liganded {[O (N) under bar OH]}(2)Ge complexes, where an E(+2) intermediate was inserted into the ArO-H bond with subsequent H-2 evolution. In contrast, substituted [O (N) under bar OMe]H-2 ligands gave [O (N) under barO(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 [O-Ar (N) under barO]H-2 ligands than for alcoholic [O-Alk (N) under barO]H-2. The thermodynamics and possible intermediates of the reactions were also investigated.