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Issue 13, 2018
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Redox and photocatalytic properties of a NiII complex with a macrocyclic biquinazoline (Mabiq) ligand

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Abstract

We present a late, first row transition metal photosensitizer that promotes photocatalytic C–C bond formation. The title compound, [Ni(Mabiq)]OTf, as well as its one-electron reduced form, Ni(Mabiq), were synthesized and molecular structures of both were obtained. The electronic structure of the reduced complex additionally was characterized by spectroscopic and DFT computational methods. Notably, [NiII(Mabiq)]OTf is photoactive: reduction of the compound was achieved photochemically upon irradiation at λ = 457 nm and reductive quenching by NEt3. The performance of [Ni(Mabiq)]OTf as a photoredox catalyst was examined in the cyclization of a bromoalkyl-substituted indole. In this reaction, the first-row transition metal compound is comparable if not superior to [Ru(bpy)3]2+ in terms of efficiency (turnover number) and chemoselectivity. Studies using a series of sacrificial donor amines indicate that the excited state redox potential of [Ni(Mabiq)]+* is ≥1.25 V vs. SCE. This value is similar to the excited state potential of commonly employed noble metal based photocatalysts. The Ni-Mabiq compound thus provides a rare example of an earth-abundant photoredox catalyst.

Graphical abstract: Redox and photocatalytic properties of a NiII complex with a macrocyclic biquinazoline (Mabiq) ligand

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Publication details

The article was received on 15 Dec 2017, accepted on 20 Feb 2018 and first published on 23 Feb 2018


Article type: Edge Article
DOI: 10.1039/C7SC05320G
Citation: Chem. Sci., 2018,9, 3313-3317
  • Open access: Creative Commons BY-NC license
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    Redox and photocatalytic properties of a NiII complex with a macrocyclic biquinazoline (Mabiq) ligand

    M. Grübel, I. Bosque, P. J. Altmann, T. Bach and C. R. Hess, Chem. Sci., 2018, 9, 3313
    DOI: 10.1039/C7SC05320G

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