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Published July 24, 2013 | Supplemental Material
Journal Article Open

Generation of Powerful Tungsten Reductants by Visible Light Excitation

Abstract

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 (λ_max ≈ 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, [Bun4N][PF_6], 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 [Bun4N][PF6]/THF solutions. The estimated reduction potential for the [W(CNIph)6]^(+)/*W couple is −2.8 V vs Cp_(2)Fe^(+/0), establishing W(CNIph)_6 as one of the most powerful photoreductants that has been generated with visible light.

Additional Information

© 2013 American Chemical Society. Received: May 10, 2013; Published: July 15, 2013. Dedicated to the memory of Nicholas J. Turro. The authors thank Jeffrey J. Warren, James R. McKone, and Oliver S. Shafaat for helpful discussions. Our work is supported by the National Science Foundation Center for Chemical Innovation in Solar Fuels (CHE-0802907); CCI postdoctoral fellowship to W.S.; and the Dow Chemical Company through the university partnership program (Agreement No. 227027AH).

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