Reversible Intramolecular Single-Electron Oxidative Addition Involving a Hemilabile Noninnocent Ligand

Hübner, Ralph; Weber, Sebastian; Strobel, Sabine; Sarkar, Biprajit; Záliš, Stanislav; Kaim, Wolfgang

doi:10.1021/om100969q

Cited by 55 publications

(41 citation statements)

References 36 publications

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“…The described example of reversible intramolecular double oxidative addition, based not on a metal redox process, but on ligand electron transfer, complements previous reactivity studies5, 23 where remote electron transfer at noninnocent ligands has activated addition reactions at the metal or at the ancillary ligand. This present example of nickel complexes thus complements previous related studies of copper,3 iridium,6, 24 ruthenium, and rhodium compounds24 and may be extended to complexes of other metals. Dinickel complexes of redox‐active quinonoid bischelate ligands, which have been well investigated by Braunstein et al.,25 might thus be modified accordingly in order to add another dimension to the systems described here.…”

Section: Resultssupporting

confidence: 86%

“…However, the hemilabile ligand itself can also be redox active, leading to potentially noninnocent behavior4 in transition metal complexes. In connection with the H 2 ‐activation research described by Ringenberg, Rauchfuss et al.,5 we have thus described a redox‐active iminobenzoquinone ligand with an additional thioether donor function, Q y =4,6‐di‐ tert‐ butyl‐ N ‐(2‐methylthiophenyl)‐ o ‐iminobenzoquinone, where the S‐donor atom coordinates to [Ir(C 5 Me 5 )] 2+ in the semiquinone state, but not in the fully reduced amidophenolate form (Scheme ) 6…”

Section: Introductionmentioning

confidence: 90%

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Correlated Coordination and Redox Activity of a Hemilabile Noninnocent Ligand in Nickel Complexes

Paretzki

Bubrin

Fiedler

et al. 2014

Chemistry A European J

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The compound [Ni(QM)2], QM = 4,6-di-tert-butyl-N-(2-methylthiomethylphenyl)-o-iminobenzoquinone, is a singlet diradical species with approximately planar configuration at the tetracoordinate metal atom and without any Ni-S bonding interaction. One-electron oxidation results in additional twofold Ni-S coordination (dNi-S ≈2.38 Å) to produce a complex cation of [Ni(QM)2](PF6) with hexacoordinate Ni(II) and two distinctly different mer-configurated tridentate ligands. The O,O'-trans arrangement in the neutral precursor is changed to an O,O'-cis configuration in the cation. The EPR signal of [Ni(QM)2](PF6) has a very large g anisotropy and the magnetic measurements indicate an S = 3/2 state. The dication was structurally characterized as [Ni(QM)2](ClO4)2 to exhibit a similar NiN2O2S2 framework as the monocation. However, the two tridentate (O,N,S) ligands are now equivalent according to the formulation [Ni(II)(QM(0))2](2+). Cyclic voltammetry reflects the qualitative structure change on the first, but not on the second oxidation of [Ni(QM)2], and spectroelectrochemistry reveals a pronounced dependence of the 800-900 nm absorption on the solvent and counterion. Reduction of the neutral form occurs in an electrochemically reversible step to yield an anion with an intense near-infrared absorption at 1345 nm (ε = 10,400 M(-1) cm(-1)) and a conventional g factor splitting for a largely metal-based spin (S = 1/2), suggesting a [(QM(·-))Ni(II)(QM(2-))](-) configuration with a tetracoordinate metal atom with antiferromagnetic Ni(II)-(QM(·-)) interactions and symmetry-allowed ligand-to-ligand intervalence charge transfer (LLIVCT). Calculations are used to understand the Ni-S binding activity as induced by remote electron transfer at the iminobenzoquinone redox system.

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Section: Resultssupporting

confidence: 86%

Section: Introductionmentioning

confidence: 90%

Correlated Coordination and Redox Activity of a Hemilabile Noninnocent Ligand in Nickel Complexes

Paretzki

Bubrin

Fiedler

et al. 2014

Chemistry A European J

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“…[11] In that case, however, the rearrangement involving a change in the metal coordination number leads to nonreversible behaviour in the cyclovoltammetric experiment, in contrast to the situation shown here. …”

Section: Discussioncontrasting

confidence: 66%

Coordination of a Hemilabile N,N,S Donor Ligand in the Redox System [CuL₂]^+/2+, L = 2‐Pyridyl‐N‐(2′‐alkylthiophenyl)methyleneimine

et al. 2011

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The new copper(I) complexes [Cu(L1)2](BF4), L1 = 2‐pyridyl‐N‐(2′‐methylthiophenyl)methyleneimine, and [Cu(L2)2](ClO4), L2 = 2‐pyridyl‐N‐(2′‐benzylthiophenyl)methyleneimine, have been prepared and structurally characterized. In contrast to the known [Cu(L1)2](ClO4)2, which exhibits partial thioether S binding to effect five‐coordinate Cu2+, the copper(I) compounds reported here contain four‐coordinate metal ions with exclusively N‐donor binding. Cyclic voltammetry reveals a fully reversible oxidation of the CuI species, which suggests a small barrier for reorganization. The reduction at negative potentials is irreversible for compounds [Cu(L)2](X) and for the structurally characterized new compound [Cu(L1)(PPh3)2](ClO4). UV/Vis spectroelectrochemistry shows the typical low‐energy absorption bands of copper(I) (MLCT transition) and copper(II) (ligand‐field transition) in the visible region; the CuII form develops an intense band at 350 nm attributed to a S‐to‐Cu ligand‐to‐metal charge transfer (LMCT).

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“…62 To determine if the redox-active ligand could induce redox activity onto another ligand, complex 81 was reacted with a source of triphenylmethyl radical (Ph 3 C ) (Scheme 32). The main organic product was found to be triphenylmethanol (Ph 3 COH), and two new rhenium complexes -dichlorido-species 82 and oxo-bridged dimer (83) were also detected. The authors propose that mixing of a populated ReQO p-bond with the ligandcentered sq À radical leads to substantial oxyl radical character (O ) for the oxo fragment, which enables the low-barrier radical coupling.…”

Section: (A) Ligand-to-substrate Single Electron Transfermentioning

confidence: 99%

New avenues for ligand-mediated processes – expanding metal reactivity by the use of redox-active catechol, o-aminophenol and o-phenylenediamine ligands

2015

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Redox-active ligands have evolved from being considered spectroscopic curiosities - creating ambiguity about formal oxidation states in metal complexes - to versatile and useful tools to expand on the reactivity of (transition) metals or to even go beyond what is generally perceived possible. This review focusses on metal complexes containing either catechol, o-aminophenol or o-phenylenediamine type ligands. These ligands have opened up a new area of chemistry for metals across the periodic table. The portfolio of ligand-based reactivity invoked by these redox-active entities will be discussed. This ranges from facilitating oxidative additions upon d(0) metals or cross coupling reactions with cobalt(iii) without metal oxidation state changes - by functioning as an electron reservoir - to intramolecular ligand-to-substrate single-electron transfer to create a reactive substrate-centered radical on a Pd(ii) platform. Although the current state-of-art research primarily consists of stoichiometric and exploratory reactions, several notable reports of catalysis facilitated by the redox-activity of the ligand will also be discussed. In conclusion, redox-active ligands containing catechol, o-aminophenol or o-phenylenediamine moieties show great potential to be exploited as reversible electron reservoirs, donating or accepting electrons to activate substrates and metal centers and to enable new reactivity with both early and late transition as well as main group metals.

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Reversible Intramolecular Single-Electron Oxidative Addition Involving a Hemilabile Noninnocent Ligand

Cited by 55 publications

References 36 publications

Correlated Coordination and Redox Activity of a Hemilabile Noninnocent Ligand in Nickel Complexes

Correlated Coordination and Redox Activity of a Hemilabile Noninnocent Ligand in Nickel Complexes

Coordination of a Hemilabile N,N,S Donor Ligand in the Redox System [CuL₂]^+/2+, L = 2‐Pyridyl‐N‐(2′‐alkylthiophenyl)methyleneimine

New avenues for ligand-mediated processes – expanding metal reactivity by the use of redox-active catechol, o-aminophenol and o-phenylenediamine ligands

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Reversible Intramolecular Single-Electron Oxidative Addition Involving a Hemilabile Noninnocent Ligand

Cited by 55 publications

References 36 publications

Correlated Coordination and Redox Activity of a Hemilabile Noninnocent Ligand in Nickel Complexes

Correlated Coordination and Redox Activity of a Hemilabile Noninnocent Ligand in Nickel Complexes

Coordination of a Hemilabile N,N,S Donor Ligand in the Redox System [CuL2]+/2+, L = 2‐Pyridyl‐N‐(2′‐alkylthio­phenyl)methyleneimine

New avenues for ligand-mediated processes – expanding metal reactivity by the use of redox-active catechol, o-aminophenol and o-phenylenediamine ligands

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Coordination of a Hemilabile N,N,S Donor Ligand in the Redox System [CuL₂]^+/2+, L = 2‐Pyridyl‐N‐(2′‐alkylthiophenyl)methyleneimine