The Oxo-Wall Remains Intact: A Tetrahedrally Distorted Co(IV)-Oxo Complex

Jindou Yang, Hai T. Dong, Mi Sook Seo, Virginia A. Larson, Yong Min Lee, Jason Shearer, Nicolai Lehnert, Wonwoo Nam

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

In this paper, we report the preparation, spectroscopic and theoretical characterization, and reactivity studies of a Co(IV)-oxo complex bearing an N4-macrocyclic coligand, 12-TBC (12-TBC = 1,4,7,10-tetrabenzyl-1,4,7,10-tetraazacyclododecane). On the basis of the ligand and the structure of the Co(II) precursor, [CoII(12-TBC)(CF3SO3)2], one would assume that this species corresponds to a tetragonal Co(IV)-oxo complex, but the spectroscopic data do not support this notion. Co K-edge XAS data show that the treatment of the Co(II) precursor with iodosylbenzene (PhIO) as an oxidant at -40 °C in the presence of a proton source leads to a distinct shift in the Co K-edge, in agreement with the formation of a Co(IV) intermediate. The presence of the oxo group is further demonstrated by resonance Raman (rRaman) spectroscopy. Interestingly, the EPR data of this complex show a high degree of rhombicity, indicating structural distortion. This is further supported by the EXAFS data. Using DFT calculations, a structural model is developed for this complex with a ligand-protonated structure that features a Co?O···HN hydrogen bond and a four-coordinate Co center in a seesaw-shaped coordination geometry. Magnetic circular dichroism (MCD) spectroscopy further supports this finding. The hydrogen bond leads to an interesting polarization of the Co-oxo ?-bonds, where one O(p) lone-pair is stabilized and leads to a regular Co(d) interaction, whereas the other ?-bond shows an inverted ligand field. The reactivity of this complex in hydrogen atom and oxygen atom transfer reactions is discussed as well.

Original languageEnglish
Pages (from-to)16943-16959
Number of pages17
JournalJournal of the American Chemical Society
Volume143
Issue number41
DOIs
StatePublished - 20 Oct 2021

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