Spin-forbidden hydrogen atom transfer reactions in a cobalt biimidazoline system

Manner, Virginia W.; Lindsay, Alexander; Mader, Elizabeth A.; Harvey, Jeremy N.; Mayer, James M.

doi:10.1039/c1sc00387a

Cited by 39 publications

(36 citation statements)

References 125 publications

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“…In view of the large SOC-induced stabilization of 8 (Figure 3a), the contribution to the HATr eaction is of interest. [23] However,s ufficient quenching by the ligand field is generally assumed for coordination compounds. [23] However,s ufficient quenching by the ligand field is generally assumed for coordination compounds.…”

Section: Zuschriftenmentioning

confidence: 99%

A Terminal Iridium Oxo Complex with a Triplet Ground State

et al. 2019

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Aterminal iridium oxocomplex with an open-shell (S = 1) ground state was isolated upon hydrogen atom transfer (HAT) from the respective iridium(II) hydroxide.E lectronic structure examinations support large spin delocalization to the oxygen atom. Selected oxot ransfer reactions indicate the ambiphilic reactivity of the iridium oxom oiety.C alorimetric and computational examinations of the HATrevealed ab ond dissociation free energy for the IrO À Hb ond that is sufficient for hydrogen atom abstraction towardsC À Hbonds and small contributions from entropya nd spin-orbit coupling to the HATthermochemistry.

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Section: Zuschriftenmentioning

confidence: 99%

A Terminal Iridium Oxo Complex with a Triplet Ground State

et al. 2019

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“…21 Our recent study of the spin-forbidden HAT reaction converting a quartet cobalt(II) complex to a singlet Co(III) product, [Co II (H 2 L) 3 ] 2+ ( S = 3/2) + XO • ( S = ½) → [Co III (H 2 L) 2 (HL)] 2+ ( S = 0) + XOH ( S = 0), concluded that the reaction occurs in two steps, with equilibrium spin isomerization to the singlet surface prior to HAT. 22 …”

Section: A Simple Kinetic Demonstration That Unpaired Spin Cannotmentioning

confidence: 99%

“…DFT calculations are known to have difficulty in reproducing the relative energies of spin states accurately. 22 Omitting these 17 cases leaves 42 comparisons, all of which have ΔΔ E ‡ /ΔΔ E ∘ > 0. In all of the cases where the calculations give a confident prediction, the spin isomer with the greater driving force has the lower barrier.…”

Section: Effects Of Spin Statementioning

confidence: 99%

Do spin state and spin density affect hydrogen atom transfer reactivity?

2014

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The prevalence of hydrogen atom transfer (HAT) reactions in chemical and biological systems has prompted much interest in establishing and understanding the underlying factors that enable this reactivity. Arguments have been advanced that the electronic spin state of the abstractor and/or the spin-density at the abstracting atom are critical for HAT reactivity. This is consistent with the intuition derived from introductory organic chemistry courses. Herein we present an alternative view on the role of spin state and spin-density in HAT reactions. After a brief introduction, the second section introduces a new and simple fundamental kinetic analysis, which shows that unpaired spin cannot be the dominant effect. The third section examines published computational studies of HAT reactions, which indicates that the spin state affects these reactions indirectly, primarily via changes in driving force. The essay concludes with a broader view of HAT reactivity, including indirect effects of spin and other properties on reactivity. It is suggested that some of the controversy in this area may arise from the diversity of HAT reactions and their overlap with proton-coupled electron transfer (PCET) reactions.

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“…[28] However, extensive previous studies on nonheme iron(IV)-oxo oxidants showed that generally the barriers on the quintet spin state surface are the lowest in energy. During the complete mechanism, these spin states remain the ground state and other spin states are well higher in energy.…”

Section: Full Papermentioning

confidence: 99%

Does Hydrogen‐Bonding Donation to Manganese(IV)–Oxo and Iron(IV)–Oxo Oxidants Affect the Oxygen‐Atom Transfer Ability? A Computational Study

Latifi

Sainna

Rybak‐Akimova

et al. 2013

Chemistry A European J

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Iron(IV)-oxo intermediates are involved in oxidations catalyzed by heme and nonheme iron enzymes, including the cytochromes P450. At the distal site of the heme in P450 Compound I (Fe(IV) -oxo bound to porphyrin radical), the oxo group is involved in several hydrogen-bonding interactions with the protein, but their role in catalysis is currently unknown. In this work, we investigate the effects of hydrogen bonding on the reactivity of high-valent metal-oxo moiety in a nonheme iron biomimetic model complex with trigonal bipyramidal symmetry that has three hydrogen-bond donors directed toward a metal(IV)-oxo group. We show these interactions lower the oxidative power of the oxidant in reactions with dehydroanthracene and cyclohexadiene dramatically as they decrease the strength of the OH bond (BDEOH ) in the resulting metal(III)-hydroxo complex. Furthermore, the distal hydrogen-bonding effects cause stereochemical repulsions with the approaching substrate and force a sideways attack rather than a more favorable attack from the top. The calculations, therefore, give important new insights into distal hydrogen bonding, and show that in biomimetic, and, by extension, enzymatic systems, the hydrogen bond may be important for proton-relay mechanisms involved in the formation of the metal-oxo intermediates, but the enzyme pays the price for this by reduced hydrogen atom abstraction ability of the intermediate. Indeed, in nonheme iron enzymes, where no proton relay takes place, there generally is no donating hydrogen bond to the iron(IV)-oxo moiety.

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Spin-forbidden hydrogen atom transfer reactions in a cobalt biimidazoline system

Cited by 39 publications

References 125 publications

A Terminal Iridium Oxo Complex with a Triplet Ground State

A Terminal Iridium Oxo Complex with a Triplet Ground State

Do spin state and spin density affect hydrogen atom transfer reactivity?

Does Hydrogen‐Bonding Donation to Manganese(IV)–Oxo and Iron(IV)–Oxo Oxidants Affect the Oxygen‐Atom Transfer Ability? A Computational Study

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