Plumbylenes based on redox-active ligands: Synthesis, optoelectronic properties and electrochemical behavior

Abstract

At present, the chemistry of low-valent derivatives of the 14th group elements continues to develop intensively, primarily tetrylenes, i.e. carbenes and their heavy analogues – silylenes, germylenes, stannylenes and plumbylenes. This is related, among other things, with their promising properties as catalysts, new materials, etc. In this range the greatest stability is demostrated by the derivatives of Pb⁺²; moreover, among those listed only for lead derivatives, the main oxidation state is +2, and not +4. Despite this, their physicochemical properties, including redox and optoelectronic features, are the least studied. In this work, we obtained four lead(II) derivatives with redox-active ligands based on Schiff bases. Both the data from electron absorption spectroscopy and the study of redox behavior by cyclic voltammetry show that the obtained products have a fairly small HOMO/LUMO gap of about 3 eV or less. Complexation with lead in all cases promotes quenching of fluorescence of ligands both in solid form and in solution. Solutions of the compounds in DMF are electrochemically reduced in the moderate (−1.5..-2.0 V vs Fc⁺/Fc) region. The product of electrochemical reduction of plumbylenes is metallic lead, which was additionally confirmed by controlled potential electrolysis and subsequent study of the deposit obtained on the cathode using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The studied plumbylenes are oxidized in DMF in a very soft potential range – +0.1.. + 0.7 V vs Fc⁺/Fc, which demonstrates the high level and availability of their HOMO. Thus, the presence of a strong electron pair donor in the coordination sphere of Pb(II) can be effectively used in the design of the plumbylenes structure in order to increase the availability of their HOMO and impart valuable and useful properties, such as the ability to readily undergo oxidative addition reactions.