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Modulation of Nickel Pyridinedicarboxamidate Complexes to Explore the Properties of High‐valent Oxidants
Author(s) -
Pirovano Paolo,
Twamley Brendan,
McDonald Aidan R.
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201704618
Subject(s) - nickel , chemistry , ligand (biochemistry) , electron paramagnetic resonance , oxidizing agent , metastability , crystallography , porphyrin , photochemistry , catalysis , electron acceptor , inorganic chemistry , organic chemistry , nuclear magnetic resonance , biochemistry , physics , receptor
High‐valent Ni oxidants have been implicated in hydrocarbon oxidation catalysis, however, little is understood about the properties of these oxidants. Herein, a family of Ni II complexes supported by a pyridinedicarboxamidate ligand and different ancillary ligands was synthesized. The series spans coordination numbers 4, 5, and 6, and contains neutral, mono‐ and di‐anionic donor types. X‐ray crystallography and magnetic measurements showed that the 4‐coordinate complexes were square planar and low spin ( S= 0) and the 5‐ and 6‐coordinate were intermediate spin ( S= 1). The Ni II complexes could be oxidized by one electron to form a series of metastable Ni III species. EPR analysis confirmed their description as S = 1 / 2 Ni III compounds with signal shape and hyperfine coupling dependent on the coordination environment. The oxidation of phenols by the Ni III species was probed, providing evidence for a correlation between oxidizing power and electron‐donating properties of the supporting ligands. Critically, we found that the pyridinedicarboxamidate ligand may be a non‐innocent proton acceptor in the oxidation reactions.