Generation of Powerful Tungsten Reductants by Visible Light Excitation

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, [Bu^<i>n</i>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^<i>n</i>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

Generation of Powerful Tungsten Reductants by Visible Light Excitation

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, [Bu^<i>n</i>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^<i>n</i>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