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1. Attempts at generating metathesis-active Fe(IV) and Co(IV) complexes via the reactions of (silox)2M(THF)2, [(silox)3M][Na(THF)2] (M = Fe, Co), and related species with propellanes and triphenylboron

   Gregory M. George, Peter T. (January 2022, Polyhedron)

   Parkin, Ged (Ed.)

   Metathetical syntheses of (silox)2M(THF)2 (1-M, Fe, Co), [(silox)3M]Na(THF)2 (2-M, Fe, Co), and (silox)3Fe(THF) (3) are presented, as are X-ray structural studies of 1-Co, 2-Fe, and 2-Co. Exposure of these complexes to 1.1.1- propellane (111P, C5H6) and 1,3-dehydroadamantane (AdP), which are known progenitors of ROMP-active alkylidenes with ruthenium, failed to elicit similar reactivity. A total of 28 complexes were subjected to 111P in attempts to make “Fe(IV)” alkylidenes capable of some form of olefin metathesis with no success. At best, catalytic ring-opening to 3-exo-methylene cyclobutylidene was evidenced. The addition of triphenylboron as a Lewis acid failed to aid in metal complex formation of the propellanes, but an unusual rearrangement of AdP was noted. In addition, 2-Fe catalyzed the conversion of 111P to 3-exo-methylene cyclobutylidene, which added twice to Ph3B, affording a structurally characterized product, Ph(κ-CH=CMeCH2BPh 

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2. 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

   https://doi.org/10.1073/pnas.2307950120  

   Li, Yan; Abelson, Chase; Que, Lawrence; Wang, Dong (December 2023, Proceedings of the National Academy of Sciences)

   The hydroxylation of C–H bonds can be carried out by the high-valent Co^III,IV₂(µ-O)₂complex2asupported by the tetradentate tris(2-pyridylmethyl)amine ligand via a Co^III₂(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 Co^III₂(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 pK_aof the system, and calculate the O–H bond strength (D_O–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 Fe^III,IV₂(µ-O)₂and Mn^III,IV₂(µ-O)₂analogs, an unexpected outcome that raises the prospects for using Co^III,IV₂(µ-O)₂species to oxidize alkane C–H bonds. 

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3. Oxidative Additions to Ti(IV) in [(dadi) ^4– ]Ti ^IV (THF) Involve Carbon–Carbon Bond Formation and Redox-Noninnocent Behavior

   https://doi.org/10.1021/acs.organomet.8b00930  

   Heins, Spencer P.; Zhang, Bufan; MacMillan, Samantha N.; Cundari, Thomas R.; Wolczanski, Peter T. (March 2019, Organometallics)
4. Revelation of Fe(V)/Fe(IV) Involvement in the Fe(VI)–ABTS System: Kinetic Modeling and Product Analysis

   https://doi.org/10.1021/acs.est.0c07792  

   Luo, Cong; Sadhasivan, Manasa; Kim, Juhee; Sharma, Virender K.; Huang, Ching-Hua (March 2021, Environmental Science & Technology)

   null (Ed.)
5. Force-Activated Spin-Crossover in Fe ²⁺ and Co ²⁺ Transition Metal Mechanophores

   https://doi.org/10.1021/acs.inorgchem.4c04732  

   Huang, Xiao; Kevlishvili, Ilia; Craig, Stephen L; Kulik, Heather J (January 2025, Inorganic Chemistry)