Preparation and Characterization of a Formally NiIV-Oxo Complex with a Triplet Ground State and Application in Oxidation Reactions

Deepika G. Karmalkar, Virginia A. Larson, Deesha D. Malik, Yong Min Lee, Mi Sook Seo, Jin Kim, Dovydas Vasiliauskas, Jason Shearer, Nicolai Lehnert, Wonwoo Nam

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

High-valent first-row transition-metal-oxo complexes are important intermediates in biologically and chemically relevant oxidative transformations of organic molecules and in the water splitting reaction in (artificial) photosynthesis. While high-valent Fe- A nd Mn-oxo complexes have been characterized in detail, much less is known about their analogues with late transition metals. In this study, we present the synthesis and detailed characterization of a unique mononuclear terminal Ni-O complex. This compound, [Ni(TAML)(O)(OH)]3-, is characterized by an intense charge-transfer (CT) band around 730 nm and has an St= 1 ground state, as determined by magnetic circular dichroism spectroscopy. From extended X-ray absorption fine structure (EXAFS), the Ni-O bond distance is 1.84 Å. Ni K edge XAS data indicate that the complex contains a Ni(III) center, which results from an unusually large degree of Ni-O π-bond inversion, with one hole located on the oxo ligand. The complex is therefore best described as a low-spin Ni(III) complex (S = 1/2) with a bound oxyl (O-) ligand (S = 1/2), where the spins of Ni and oxyl are ferromagnetically coupled, giving rise to the observed St= 1 ground state. This bonding description is roughly equivalent to the presence of a Ni-O single (σ) bond. Reactivity studies show that [Ni(TAML)(O)(OH)]3-is a strong oxidant capable of oxidizing thioanisole and styrene derivatives with large negative ρ values in the Hammett plot, indicating its electrophilic nature. The intermediate also shows high reactivity in C-H bond activation of hydrocarbons with a kinetic isotope effect of 7.0(3) in xanthene oxidation.

Original languageEnglish
Pages (from-to)22698-22712
Number of pages15
JournalJournal of the American Chemical Society
Volume144
Issue number49
DOIs
StatePublished - 14 Dec 2022

Bibliographical note

Funding Information:
This work was supported by a grant from the National Science Foundation (CHE-1900380 to N.L. and J.S.). This work was also supported by the NRF of Korea through CRI (NRF-2021R1A3B1076539 to W.N.) and the Basic Science Research Program (NRF-2020R1I1A1A01074630 to Y.M.L. and NRF-2019R1I1A1A01055822 to M.S.S.). V.A.L. acknowledges support from a University of Michigan Rackham Predoctoral Fellowship.

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.

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