Easily electroreducible halogen-free germanium complexes with biologically active pyridines

The green conversion of germanium dioxide into soluble non-halogenated forms suitable for further processing occurs smoothly and in high yields under the action of 3,5-di-tert-butylbenzene-1,2-diol in presence of biologically active N-donor ligands L. The formed hexacoordinated germanium catecholate complexes (DTBCat)(2)GeL2 (DTBCat = 3,5-di-tert-butylcatecholate, L = nicotinic acid, nicotinamide and isoniazid) 1-3 are air stable and soluble in common organic solvents. These new complexes are easily reducible at a glassy carbon electrode in DMF/0.1 M Bu4NBF4 at the cathodic potentials remarkably less negative than those of the reduction of parent non-coordinated N-donor ligands L; the corresponding anodic shifts for 1-3 are 0.598, 1.009 and 0.978 V, respectively. The ease of the electrochemical reduction and the energy of electron donation from the ligands L to germanium in 1-3 are in good agreement with DFT B3LYP/def2tzvp analysis and the stabilization energies of these germanium complexes.