Donor-acceptor complexes of main group 14 elements with α-diimines and catecholate ligands

A series of new six-coordinate silicon, germanium, and tin complexes based on 3,6-di-tert-butyl-o-benzoquinone with N-donor ligands (1,10-phenanthroline and 2,2′-bipyridine) were synthesized and structurally and spectrally characterized. According to the results of electrochemical measurements, the complexes can be oxidized or reduced (they are redox amphoteric) due to the presence of redox-active ligands. The electronic absorption spectra of the compounds show absorption in the 450–500 nm range, which accounts for their intense color. This absorption band is blue-shifted with increasing solvent polarity. The combination of the spectral characteristics and results of quantum chemical calculations indicates that the synthesized silicon, germanium, and tin complexes can be considered as donor-acceptor chromophores with photoinduced ligand-to-ligand charge transfer between the diimine moiety and catechols.