rhenium ring is one of the rarest and most hard-to-find elements in the earth’s crust. This rare metal is widely used in superalloys for jet engines, where it imparts strength at high temperatures. Its price has not recovered to its 2008 peak, and it remains vulnerable to demand fluctuations caused by changes in the economy.
Rhenum is a heavy transition metal, which shows good resistance to poisons, especially nitrogen oxides, sulfur and phosphorus. Among its many applications, it has been used in selective hydrogenation and crude oil reforming.
We prepared photocatalytic CO2 reduction systems by using Re-rings as PSs and investigated their reductive quenching with triethanolamine (TEOA). The oxidation power of the Re-rings in the excited state was found to be significantly increased after reductive quenching with TEOA.
The reductive quenching of the Re-rings with TEOA was observed to be dependent on their p-p interactions and their lifetime in solution. We obtained Stern-Volmer plots and determined the quenching rate constants, kq.
These results indicate that the OERS of the Re unit(s) in the ring-shaped tetranuclear complexes were accumulated during irradiation. These OERS induced the inner-filter effect, which lowered the absorption of incoming photons. The molar extinction coefficient of the OERS of R4P(4)4+ was found to be 1760 M-1 cm-1, which is higher than those of the mononuclear complex P-Re-P+.
The ring-shaped tetranuclear Re complexes are promising photocatalytic CO2 reduction catalysts. These complexes have high formation yields of OERS and strong oxidation powers in the excited state.