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

Michael Grübel, Irene Bosque, Philipp J. Altmann, Thorsten Bach, Corinna R. Hess

Research output: Contribution to journalArticlepeer-review

45 Scopus citations

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.

Original languageEnglish
Pages (from-to)3313-3317
Number of pages5
JournalChemical Science
Volume9
Issue number13
DOIs
StatePublished - 2018

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