Generation of Powerful Tungsten Reductants by Visible Light Excitation

• Published in: Journal of the American Chemical Society Vol. 135; no. 29; pp. 10614 - 10617
• Main Authors: Sattler, Wesley, Ener, Maraia E, Blakemore, James D, Rachford, Aaron A, LaBeaume, Paul J, Thackeray, James W, Cameron, James F, Winkler, Jay R, Gray, Harry B
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.07.2013
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja4047119

The homoleptic arylisocyanide tungsten complexes, W(CNXy)6 and W(CNIph)6 (Xy = 2,6-dimethylphenyl, Iph = 2,6-diisopropylphenyl), display intense metal to ligand charge transfer (MLCT) absorptions in the visible region (400–550 nm). MLCT emission (λmax ≈ 580 nm) in tetrahydrofuran (THF) solution at rt is observed for W(CNXy)6 and W(CNIph)6 with lifetimes of 17 and 73 ns, respectively. Diffusion-controlled energy transfer from electronically excited W(CNIph)6 (*W) to the lowest energy triplet excited state of anthracene (anth) is the dominant quenching pathway in THF solution. Introduction of tetrabutylammonium hexafluorophosphate, [Bu n 4N][PF6], to the THF solution promotes formation of electron transfer (ET) quenching products, [W(CNIph)6]+ and [anth]•–. ET from *W to benzophenone and cobalticenium also is observed in [Bu n 4N][PF6]/THF solutions. The estimated reduction potential for the [W(CNIph)6]+/*W couple is −2.8 V vs Cp2Fe+/0, establishing W(CNIph)6 as one of the most powerful photoreductants that has been generated with visible light.