Redox-Active Bis(phenolate) N-Heterocyclic Carbene [OCO] Pincer Ligands Support Cobalt Electron Transfer Series Spanning Four Oxidation States
| Autor: | Nicolaas P. van Leest, Quinton J. Bruch, Brooke N. Livesay, Jake D. Soper, John Bacsa, Kenneth I. Hardcastle, Bas de Bruin, Caleb F. Harris, Michael B. Bayless, Matthew P. Shores |
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| Přispěvatelé: | Nature Inspired Transition Metal Catalysis (HIMS, FNWI), Faculty of Science, HIMS Other Research (FNWI), Sustainable Chemistry, Homogeneous and Supramolecular Catalysis (HIMS, FNWI) |
| Rok vydání: | 2017 |
| Předmět: |
010405 organic chemistry
Ligand chemistry.chemical_element 010402 general chemistry Photochemistry 01 natural sciences Medicinal chemistry 0104 chemical sciences Pincer movement Inorganic Chemistry Metal Electron transfer chemistry.chemical_compound chemistry visual_art visual_art.visual_art_medium Redox active Physical and Theoretical Chemistry Cobalt Carbene |
| Zdroj: | Inorganic Chemistry, 56(20), 12421-12435. American Chemical Society |
| ISSN: | 1520-510X 0020-1669 |
| DOI: | 10.1021/acs.inorgchem.7b01906 |
| Popis: | A new family of low-coordinate Co complexes supported by three redox-noninnocent tridentate [OCO] pincer-type bis(phenolate) N-heterocyclic carbene (NHC) ligands are described. Combined experimental and computational data suggest that the charge-neutral four-coordinate complexes are best formulated as Co(II) centers bound to closed-shell [OCO]2– dianions, of the general formula [(OCO)CoIIL] (where L is a solvent-derived MeCN or THF). Cyclic voltammograms of the [(OCO)CoIIL] complexes reveal three oxidations accessible at potentials below 1.2 V vs Fc+/Fc, corresponding to generation of formally Co(V) species, but the true physical/spectroscopic oxidation states are much lower. Chemical oxidations afford the mono- and dications of the imidazoline NHC-derived complex, which were examined by computational and magnetic and spectroscopic methods, including single-crystal X-ray diffraction. The metal and ligand oxidation states of the monocationic complex are ambiguous; data are consistent with formulation as either [(SOCO)CoIII(THF)2]+ containing a closed-shell [SOCO]2– diphenolate ligand bound to a S = 1 Co(III) center, or [(SOCO•)CoII(THF)2]+ with a low-spin Co(II) ion ferromagnetically coupled to monoanionic [SOCO•]− containing a single unpaired electron distributed across the [OCO] framework. The dication is best described as [(SOCO0)CoII(THF)3]2+, with a single unpaired electron localized on the d7 Co(II) center and a doubly oxidized, charge-neutral, closed-shell SOCO0 ligand. The combined data provide for the first time unequivocal and structural evidence for [OCO] ligand redox activity. Notably, varying the degree of unsaturation in the NHC backbone shifts the ligand-based oxidation potentials by up to 400 mV. The possible chemical origins of this unexpected shift, along with the potential utility of the [OCO] pincer ligands for base-metal-mediated organometallic coupling catalysis, are discussed. |
| Databáze: | OpenAIRE |
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