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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.
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Ligand and Linkage Isomers of Bis(ethylthiocarbamato) Copper Complexes with Cyclic C 6 H 8 Backbone Substituents: Synthesis, Characterization, and Antiproliferation Activity
Abstract A series of isomeric bis(alkylthiocarbamate) copper complexes have been synthesized, characterized, and evaluated for antiproliferation activity. The complexes were derived from ligand isomers with 3‐methylpentyl (H2L2) and cyclohexyl (H2L3) backbone substituents, which each yield a pair of linkage isomers. The thermodynamic products CuL2a/3ahave two imino N and two S donors resulting in three five‐member chelate rings (555 isomers). The kinetic isomers CuL2b/3bhave one imino and one hydrazino N donor and two S donors resulting in four‐, six‐, and five‐member rings (465 isomers). The 555 isomers have more accessible CuII/Ipotentials (E1/2=−811/−768 mV vs. ferrocenium/ferrocene) and lower energy charge transfer bands than their 465 counterparts (E1/2=−923/‐854 mV). Antiproliferation activities were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR‐90) using the MTT assay. CuL2awas potent (A549EC50=0.080 μM) and selective (IMR‐90EC50/A549EC50=25) for A549. Its linkage isomer CuL2bhad equivalent A549 activity, but lower selectivity (IMR‐90EC50/A549EC50=12.5). The isomers CuL3aand CuL3bwere less potent withA549EC50 values of 1.9 and 0.19 M and less selective withIMR‐90EC50/A549EC50ratios of 2.3 and 2.65, respectively. There was no correlation between reduction potential and A549 antiproliferation activity/selectivity.
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- Award ID(s):
- 1800245
- PAR ID:
- 10642568
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- European Journal of Inorganic Chemistry
- Volume:
- 26
- Issue:
- 34
- ISSN:
- 1434-1948
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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