Nickel(IV) Intermediates in Aminoquinoline-Directed C(sp<sup>2</sup>)–C(sp<sup>3</sup>) Coupling

Milbauer, Michael W.; Kampf, Jeff W.; Sanford, Melanie S.

doi:10.1021/jacs.2c10778

Cited by 13 publications

(11 citation statements)

References 53 publications

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“…The best performers in terms of luminescence and MLCT lifetimes are currently based on Cr 0 and Mn I , for which chelating arylisocyanides are important . Ni IV does not seem to have been considered yet from a photophysical perspective. , Square-planar Ni II (3d 8 ) compounds represent a great challenge that has now been taken on by several research groups.…”

Section: Discussionmentioning

confidence: 99%

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Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d⁶ Complexes with Cr⁰, Mn^I, Fe^II, and Co^III

2023

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Many coordination complexes and organometallic compounds with the 4d6 and 5d6 valence electron configurations have outstanding photophysical and photochemical properties, which stem from metal-to-ligand charge transfer (MLCT) excited states. This substance class makes extensive use of the most precious and least abundant metal elements, and consequently there has been a long-standing interest in first-row transition metal compounds with photoactive MLCT states. Semiprecious copper(I) with its completely filled 3d subshell is a relatively straightforward and well explored case, but in 3d6 complexes the partially filled d-orbitals lead to energetically low-lying metal-centered (MC) states that can cause undesirably fast MLCT excited state deactivation. Herein, we discuss recent advances made with isoelectronic Cr0, MnI, FeII, and CoIII compounds, for which long-lived MLCT states have become accessible over the past five years. Furthermore, we discuss possible future developments in the search for new first-row transition metal complexes with partially filled 3d subshells and photoactive MLCT states for next-generation applications in photophysics and photochemistry.

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Section: Discussionmentioning

confidence: 99%

“…89 Ni IV does not seem to have been considered yet from a photophysical perspective. 195,196 Square-planar Ni II (3d 8 ) compounds represent a great challenge that has now been taken on by several research groups.…”

Section: Discussionmentioning

confidence: 99%

Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d⁶ Complexes with Cr⁰, Mn^I, Fe^II, and Co^III

2023

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“…The primary pathways considered were: (A) concerted, intermolecular protonation (Scheme A), (B) concerted intramolecular protonation (Scheme B), and (C) stepwise, S E Ar-type protonation followed by elimination, either inter- or intramolecular (Scheme C). We did not consider mechanisms involving formation of (bpy)Ni IV (Ar)(X)(H)(A) because nickel(IV) generally requires strong oxidants to be accessible. − …”

Section: Discussionmentioning

confidence: 99%

Protodemetalation of (Bipyridyl)Ni(II)–Aryl Complexes Shows Evidence for Five-, Six-, and Seven-Membered Cyclic Pathways

et al. 2023

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Protonation of C−M bonds and its microscopic reverse, metalation of C−H bonds, are fundamental steps in a variety of metal-catalyzed processes. As such, studies on protonation of C−M bonds can shed light on C−H activation. We present here studies on the rate of protodemetalation (PDM) of a suite of arylnickel(II) complexes with various acids that provide evidence for a concerted, cyclic transition state for the PDM of C−Ni bonds and demonstrate that five-, six-, and seven-membered transition states are particularly favorable. Our data show that while the rate of protodemetalation of arylnickel(II) complexes scales with acidity for many acids, several are faster than predicted by pK a . For example, while acetic acid and acetohydroxamic acid are much less acidic than HCl, they both protodemetalate arylnickel(II) complexes significantly faster than HCl. Our data also show how in the case of acetohydroxamic acid, a seven-membered cyclic transition state (CH 3 C(O)NHOH) can be more favorable than a six-membered transition state (CH 3 C(O)NHOH). Similarly, five-membered transition states, such as for pyrazole, are highly favorable as well. Comparison of transition state polarization (from density functional theory) compares these new nickel transition states to betterstudied precious-metal systems and demonstrates how the base can change the polarization of the transition state giving rise to opposing electronic preferences. Collectively, these studies suggest several new avenues for study in C−H activation as well as approaches to accelerate or slow protodemetalation in nickel catalysis.

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“…We did not consider mechanisms involving formation of (bpy)Ni IV (Ar)(X)(H)(A) because nickel(IV) generally requires strong oxidants to be accessible. [71][72][73][74] Ionized nickel complexes were the focus because they dominate in polar solvents and because there was little change in rate when we change the halide identity. 61 Finally, all considered mechanisms involve a bimolecular reaction between one nickel complex and one molecule of acid in the transition state because our VTNA experi-ments revealed that the rate of PDM with HCl1,4-dioxane and AcOH were both first-order in [nickel] and [HA].…”

Section: Discussionmentioning

confidence: 99%

Protodemetalation of (bpy)Ni(II)–Aryl Complexes Shows Evi-dence for 5, 6, and 7-Membered Cyclic Pathways

Piszel

Orzolek

Olszewski

et al. 2023

Preprint

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Protonation of C–M bonds and its microscopic reverse, metalation of C–H bonds, are fundamental steps in a variety of metal-catalyzed processes. As such, studies on protonation of C–M bonds can shed light on C–H activation. We present here studies on the rate of protodemetalation (PDM) of a suite of arylnickel(II) complex-es with various acids that provide evidence for a concerted, cyclic transition state for the PDM of C–Ni bonds and demonstrate that five, six, and seven-membered transition states are particularly favorable. Our data show that while the rate of protodemetalation of arylnickel(II) complexes scales with acidity for many acids, several are faster than predicted by pKa. For example, while acetic acid and acetohydroxamic acid are much less acid-ic than HCl, they both protodemetalate arylnickel(II) complexes significantly faster than HCl. Our data also shows how in the case of acetohydroxamic acid, a seven-membered cyclic transition state (CH3C(O)NHOH) can be more favorable than a six-membered transition state (CH3C(O)NHOH). Similarly, five-membered transition states, such as for pyrazole, are highly favorable as well. Comparison of transition-state polarization (from den-sity functional theory) compares these new nickel transition states to better-studied precious metal systems and demonstrates how the base can change the polarization of the transition state giving rise to opposing electron-ic preferences. Collectively, these studies suggest several new avenues for study in C–H activation as well as approaches to accelerate or slow protodemetalation in nickel catalysis.

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Nickel(IV) Intermediates in Aminoquinoline-Directed C(sp²)–C(sp³) Coupling

Cited by 13 publications

References 53 publications

Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d⁶ Complexes with Cr⁰, Mn^I, Fe^II, and Co^III

Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d⁶ Complexes with Cr⁰, Mn^I, Fe^II, and Co^III

Protodemetalation of (Bipyridyl)Ni(II)–Aryl Complexes Shows Evidence for Five-, Six-, and Seven-Membered Cyclic Pathways

Protodemetalation of (bpy)Ni(II)–Aryl Complexes Shows Evi-dence for 5, 6, and 7-Membered Cyclic Pathways

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Nickel(IV) Intermediates in Aminoquinoline-Directed C(sp2)–C(sp3) Coupling

Cited by 13 publications

References 53 publications

Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d6 Complexes with Cr0, MnI, FeII, and CoIII

Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d6 Complexes with Cr0, MnI, FeII, and CoIII

Protodemetalation of (Bipyridyl)Ni(II)–Aryl Complexes Shows Evidence for Five-, Six-, and Seven-Membered Cyclic Pathways

Protodemetalation of (bpy)Ni(II)–Aryl Complexes Shows Evi-dence for 5, 6, and 7-Membered Cyclic Pathways

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Nickel(IV) Intermediates in Aminoquinoline-Directed C(sp²)–C(sp³) Coupling

Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d⁶ Complexes with Cr⁰, Mn^I, Fe^II, and Co^III

Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d⁶ Complexes with Cr⁰, Mn^I, Fe^II, and Co^III