Synthesis of 2,6-(diquinoline-8-yl)pyridine for Mn(II) Photoactive Complexes

Abstract

Transition metal complexes with charge-separated excited states show many attractive properties that make them useful in various applications such as solar energy conversion, molecular wires, and photoredox catalysis. This has been observed in complexes of 2nd and 3rd row transition metals, and the most commonly used are d6 transition metals including Ir(III), Ru(II), and Re(I). These metals, however, are not practical for large scale applications due to their scarcity and high prices. Manganese, a first-row transition metal, is an attractive alternative due to its abundance and low toxicity. The most stable oxidation state of manganese, Mn(II), has the potential to yield bench-stable compounds that can be studied without the need for strictly controlled conditions. In this research, we selected and synthesized the ligand 2,6-(diquinoline-8- yl)pyridine (dqp) and attempted the synthesis of [Mn(dqp)]2+. Using a previously reported synthetic pathway, dqp was successfully prepared and its electronic absorption spectrum was obtained. However, the attempts toward coordination and crystallization of [Mn(dqp)]2+ yielded the protonated dqp. As a result, further research will continue to focus on the coordination of dqp to Mn(II) to facilitate the study of its electronics and the comparison with Mn(II) complexes of other varying ligands. By characterizing and studying their photophysical properties, we can better understand the influence of tridentate polypyridyl ligands on the behavior of Mn(II) complexes.