Tetrahedral to Octahedral Nickel(II) as an Initiation Step in Metallaphotoredox Catalysis

28 April 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

In this work we seek to understand the pre-catalystic initiation steps between two metallaphotoredox catalysts Ir(III) ((Ir[dF(CF3)ppy]2}(dtbbpy))PF6) and Ni(II) ((4,4'-dtbbpy)NiCl2) using a combination of X-ray and optical spectroscopies. We observe two steps: first, photoexcitation produces the expected intramolecular oxidation of Ir(III) to Ir(IV)(dtbbpy)•- correlated to the Ir metal-to-ligand charge transfer state, rather than Ir(II) which is often reported in literature. Second, the 4-coordinate Ni(II) starting species evolves to a 6-coordinate Ni(II) species after oxidation by Ir(IV)(dtbbpy)•-. We conclude by proposing the identity of the 6-coordinate Ni(II) species and its potential importance in the pre-mechanistic step prior to Ni entering the catalytic cycle. This neglected 6-coordinate Ni(II) intermediate could help to unravel the poorly understood initiation step in these metallaphotoredox C_sp3-C_sp2 cross-coupling reactions.

Keywords

iridium
nickel
X-ray
coordination
metallaphotoredox
oxidation
tetrahedral
octahedral
kinetics
initiation
Ir(III)
Ir(II)
Ir(IV)

Supplementary materials

Title
Description
Actions
Title
Supporting Information: Direct Nickel(II) Oxidation as an Initiation Step in Metallaphotoredox Catalysis
Description
Supporting information to main manuscript including optical spectroscopy, sample preparations, and data analysis descriptions.
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