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  • 10 6 -fold faster C–H bond hydroxylation by a Co III,IV 2 (µ-O) 2 complex [via a Co III 2 (µ-O)(µ-OH) intermediate] versus its Fe III Fe IV analog
Title: 10 6 -fold faster C–H bond hydroxylation by a Co III,IV 2 (µ-O) 2 complex [via a Co III 2 (µ-O)(µ-OH) intermediate] versus its Fe III Fe IV analog
The hydroxylation of C–H bonds can be carried out by the high-valent CoIII,IV2(µ-O)2complex2asupported by the tetradentate tris(2-pyridylmethyl)amine ligand via a CoIII2(µ-O)(µ-OH) intermediate (3a). Complex3acan be independently generated either by H-atom transfer (HAT) in the reaction of2awith phenols as the H-atom donor or protonation of its conjugate base, the CoIII2(µ-O)2complex1a. Resonance Raman spectra of these three complexes reveal oxygen-isotope-sensitive vibrations at 560 to 590 cm−1associated with the symmetric Co–O–Co stretching mode of the Co2O2diamond core. Together with a Co•••Co distance of 2.78(2) Å previously identified for1aand2aby Extended X-ray Absorption Fine Structure (EXAFS) analysis, these results provide solid evidence for their “diamond core” structural assignments. The independent generation of3aallows us to investigate HAT reactions of2awith phenols in detail, measure the redox potential and pKaof the system, and calculate the O–H bond strength (DO–H) of3ato shed light on the C–H bond activation reactivity of2a. Complex3ais found to be able to transfer its hydroxyl ligand onto the trityl radical to form the hydroxylated product, representing a direct experimental observation of such a reaction by a dinuclear cobalt complex. Surprisingly, reactivity comparisons reveal2ato be 106-fold more reactive in oxidizing hydrocarbon C–H bonds than corresponding FeIII,IV2(µ-O)2and MnIII,IV2(µ-O)2analogs, an unexpected outcome that raises the prospects for using CoIII,IV2(µ-O)2species to oxidize alkane C–H bonds.  more » « less
Award ID(s):
2102339
PAR ID:
10614887
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
National Academy of Sciences, USA
Date Published:
Journal Name:
Proceedings of the National Academy of Sciences
Volume:
120
Issue:
51
ISSN:
0027-8424
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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