Supramolecular multi-electron redox photosensitisers comprising a ring-shaped Re() tetranuclear complex and a polyoxometalate

• Published in: Chemical science (Cambridge) Vol. 14; no. 3; pp. 691 - 74
• Main Authors: Takahashi, Maria, Asatani, Tsuyoshi, Morimoto, Tatsuki, Kamakura, Yoshinobu, Fujii, Kotaro, Yashima, Masatomo, Hosokawa, Naoki, Tamaki, Yusuke, Ishitani, Osamu
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 18-01-2023
• Subjects: Carbon dioxide; Catalysts; Chemical synthesis; Electrons; Polyoxometallates; Reducing agents; Triethanolamine
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/d2sc04252e

Redox photosensitisers (PSs) play essential roles in various photocatalytic reactions. Herein, we synthesised new redox PSs of 1 : 1 supramolecules that comprise a ring-shaped Re(
i
) tetranuclear complex with 4+ charges and a Keggin-type heteropolyoxometalate with 4− charges. These PSs photochemically accumulate multi-electrons in one molecule (three or four electrons) in the presence of an electron donor and can supply electrons with different reduction potentials. PSs were successfully applied in the photocatalytic reduction of CO
2
using catalysts (Ru(
ii
) and Re(
i
) complexes) and triethanolamine as a reductant. In photocatalytic reactions, these supramolecular PSs supply a different number of electrons to the catalyst depending on the redox potential of the intermediate, which is made from the one-electron-reduced species of the catalyst and CO
2
. Based on these data, information on the reduction potentials of the intermediates was obtained.
Supramolecular photosensitisers comprising a ring-shaped Re(
i
) tetranuclear complex and a Keggin-type heteropolyoxometalate were synthesised. They can photochemically accumulate four electrons and supply them for the photocatalytic CO
2
reduction.