Enzyme-Like Hydroxylation of Aliphatic C–H Bonds From an Isolable Co-Oxo Complex

Goetz, McKenna K.; Schneider, Joseph; Filatov, Alexander S.; Jesse, Kate; Anderson, John S.

doi:10.1021/jacs.1c09280

Cited by 22 publications

(27 citation statements)

References 99 publications

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“…Identification and reactivity studies of high-valent Fe-OH , or Mn-OH , species are reported in the literature. However, to the best of our knowledge, spectroscopic characterization and reactivity studies of the Co-OH complex above +III redox level is not explored, although a few Co III (OH) complex has been characterized spectroscopically. , Characterization of metastable reaction intermediates plays a key role in understanding the reaction mechanism of several bioinspired reactions. A few Co-oxygen reaction intermediates, such as Co III (O 2 • ), Co III (O 2 – ), and Co IV (O) species, have been characterized, and their reactivities were investigated .…”

Section: Resultsmentioning

confidence: 99%

Characterization of Reaction Intermediates Involved in the Water Oxidation Reaction of a Molecular Cobalt Complex

et al. 2022

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Molecular cobalt(III) complexes of bis-amidate-bis-alkoxide ligands, (Me4N)[CoIII(L1)] (1) and (Me4N)[CoIII(L2)] (2), are synthesized and assessed through a range of characterization techniques. Electrocatalytic water oxidation activity of the Co complexes in a 0.1 M phosphate buffer solution revealed a ligand-centered 2e–/1H+ transfer event at 0.99 V followed by catalytic water oxidation (WO) at an onset overpotential of 450 mV. By contrast, 2 reveals a ligand-based oxidation event at 0.9 V and a WO onset overpotential of 430 mV. Constant potential electrolysis study and rinse test experiments confirm the homogeneous nature of the Co complexes during WO. The mechanistic investigation further shows a pH-dependent change in the reaction pathway. On the one hand, below pH 7.5, two consecutive ligand-based oxidation events result in the formation of a CoIII(L2–)(OH) species, which, followed by a proton-coupled electron transfer reaction, generates a CoIV(L2–)(O) species that undergoes water nucleophilic attack to form the O–O bond. On the other hand, at higher pH, two ligand-based oxidation processes merge together and result in the formation of a CoIII(L2–)(OH) complex, which reacts with OH– to yield the O–O bond. The ligand-coordinated reaction intermediates involved in the WO reaction are thoroughly studied through an array of spectroscopic techniques, including UV–vis absorption spectroscopy, electron paramagnetic resonance, and X-ray absorption spectroscopy. A mononuclear CoIII(OH) complex supported by the one-electron oxidized ligand, [CoIII(L3–)(OH)]−, a formal CoIV(OH) complex, has been characterized, and the compound was shown to participate in the hydroxide rebound reaction, which is a functional mimic of Compound II of Cytochrome P450.

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Section: Resultsmentioning

confidence: 99%

Characterization of Reaction Intermediates Involved in the Water Oxidation Reaction of a Molecular Cobalt Complex

et al. 2022

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“…This lability of the pyrazolyl N–B linkage also reduces the chemical and thermal stability of tris (pyrazolyl)borates . Compared with emerging scorpionate ligands, classic tris (pyrazolyl)borates are relatively weak electron donors, a limitation when studying high-valent reactive metals …”

Section: Introductionmentioning

confidence: 99%

Site-Isolated Main-Group Tris(2-pyridyl)borate Complexes by Pyridine Substitution and Their Ring-Opening Polymerization Catalysis

Qian

Comito

2022

Inorg. Chem.

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Tris(2-pyridyl)borates are an emerging class of scorpionate ligands, distinguished as exceptionally robust and electron-donating. However, the rapid formation of inert homoleptic complexes with divalent metals has so far limited their catalytic utility. We report site-isolating tris(2-pyridyl)borate ligands, bearing isopropyl, tert-butyl, and mesityl substituents at the pyridine 6-position to suppress the formation of inert homoleptic complexes. These ligands form the first 1:1 complexes between tris(2-pyridyl)borates and Mg2+, Zn2+, or Ca2+, with isopropyl-substituted TpyiPrH showing the most generality. Single-crystal X-ray diffraction analysis of the resulting complexes and comparison to density functional theory (DFT) models showed geometric distortions driven by steric repulsion between the pyridine 6-substituents and the hexamethyldisilazide (HMDS–, –N(SiMe3)2) anion. We show that this steric profile is a feature of the six-membered pyridine ring and contrasts with more established tris(pyrazolyl)borate and tris(imidazoline)borate scorpionate complexes. TpyiPrMg(HMDS) (1) and its zinc analogue are moderately active for the controlled polymerization of l-lactide, ε-caprolactone, and trimethylene carbonate. Furthermore, 1 gives controlled polymerization under more demanding melt-phase polymerization conditions at 100 °C, and block copolymerization of ε-caprolactone and trimethylene carbonate. These results will enable useful catalysis and coordination chemistry studies with tris(2-pyridyl)borates, and characterizes their structural complementarity to more familiar scorpionate ligands.

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“…The discoveries of high-valent metal-oxo species as key intermediates in a variety of enzymatic transformations have inspired numerous biomimetic and bio-inspired efforts trying to understand the structural and spectroscopic properties and substrate oxidation reactivities of these species. , While a large inventory of synthetic M(IV)O complexes for first-row early and middle transition metal elements (Cr, Mn, and Fe) have become available, high-valent metal-oxo complexes for late transition metals (Co, Ni, and Cu) are rare, as predicted by the classic bonding theory. , Alternatively, diverging the synthetic effort from the metal-oxo territory to develop non-oxo-metal complexes of late transition metals appears to be an effective strategy that provides more flexibility to study the rich chemistry of their high-valent derivatives . For example, a number of groups, including us, have described oxo- and non-oxo-Co(IV) species capable of oxidizing sp 3 C–H bonds. − For Ni and Cu, the +3 oxidation state is typically considered as “high valent”. A number of Ni(III)- and Cu(III)-hydroxo, carboxylate, and halide complexes are strong oxidants and hydrogen atom transfer (HAT) reagents; − however, examples of these two metals having formal +4 oxidation states are rare.…”

Section: Introductionmentioning

confidence: 99%

C–H Bond Activation by a Mononuclear Nickel(IV)-Nitrate Complex

et al. 2022

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The recent focus on developing high-valent non-oxo-metal complexes for late transition metals has proven to be an effective strategy to study the rich chemistry of these high-valent species while bypassing the synthetic challenges of obtaining the oxo-metal counterparts. In our continuing work of exploring late transition metal complexes of unusually high oxidation states, we have obtained in the present study a formal mononuclear Ni(IV)-nitrate complex (2) upon 1-e − oxidation of its Ni(III) derivatives (1-OH and 1-NO 3 ). Characterization of these Ni complexes by combined spectroscopic and computational approaches enables deep understanding of their geometric and electronic structures, bonding interactions, and spectroscopic properties, showing that all of them are square planar complexes and exhibit strong πcovalency with the amido N-donors of the N3 ligand. Furthermore, results obtained from X-ray absorption spectroscopy and density functional theory calculations provide strong support for the assignment of the Ni(IV) oxidation state of complex 2, albeit with strong ligand-to-metal charge donation. Notably, 2 is able to oxidize hydrocarbons with C−H bond strength in the range of 76−92 kcal/mol, representing a rare example of high-valent late transition metal complexes capable of activating strong sp 3 C−H bonds.

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Enzyme-Like Hydroxylation of Aliphatic C–H Bonds From an Isolable Co-Oxo Complex

Cited by 22 publications

References 99 publications

Characterization of Reaction Intermediates Involved in the Water Oxidation Reaction of a Molecular Cobalt Complex

Characterization of Reaction Intermediates Involved in the Water Oxidation Reaction of a Molecular Cobalt Complex

Site-Isolated Main-Group Tris(2-pyridyl)borate Complexes by Pyridine Substitution and Their Ring-Opening Polymerization Catalysis

C–H Bond Activation by a Mononuclear Nickel(IV)-Nitrate Complex

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