Crystallographic Snapshots of the Bond‐Breaking Isomerization Reactions Involving Nickel(II) Complexes with Hemilabile Ligands

Machan, Charles W.; Lifschitz, Alejo M.; Stern, Charlotte L.; Sarjeant, Amy A.; Mirkin, Chad A.

doi:10.1002/anie.201107620

Cited by 10 publications

(7 citation statements)

References 47 publications

(52 reference statements)

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“…The weak donors can bind to the metal center, dissociate to form a low-coordinate species, or be displaced by solvent or another external donor ligand. In some cases, the binding modes interconvert rapidly (“dynamic hemilability”), while in other cases isomerization can be slow or require a chemical impetus (“static hemilability”). , Crystallographic characterization can readily identify binding modes in the solid state. , It is more difficult to probe the binding mode of a hemilabile ligand in solution.…”

Section: Introductionmentioning

confidence: 99%

Mapping the Binding Modes of Hemilabile Pincer–Crown Ether Ligands in Solution Using Diamagnetic Anisotropic Effects on NMR Chemical Shift

et al. 2017

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A protocol for identifying ligand binding modes in a series of iridium pincer complexes bearing hemilabile aza-crown ether ligands has been developed using readily accessible NMR methods. The approach was tested on a collection of 13 structurally diverse pincer-crown ether complexes that include several newly characterized species. New synthetic routes enable facile interconversion of coordination modes and supporting ligands. Detailed structural assignments of five complexes reveal that the difference in chemical shift (Δδ) between geminal protons in the crown ether is influenced by diamagnetic anisotropy arising from halides and other ligands in the primary coordination sphere. The average difference in chemical shift between diastereotopic geminal protons in the crown ether macrocycle (Δδ), as determined through a single H-C HSQC experiment, provides information on the pincer ligand binding mode by establishing whether the macrocycle is in close proximity to the metal center. The Δδ values for binding modes that involve chelating ether(s) bound to iridium are roughly 2-fold larger than those for tridentate complexes with no Ir-O bonds.

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Section: Introductionmentioning

confidence: 99%

Mapping the Binding Modes of Hemilabile Pincer–Crown Ether Ligands in Solution Using Diamagnetic Anisotropic Effects on NMR Chemical Shift

et al. 2017

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“…Hemilabile ligands1 are increasingly acknowledged as valuable components of functional coordination compounds 2. The control of hemilability beyond equilibria situations is an attractive goal, for example, in catalysis 1.…”

Section: Introductionmentioning

confidence: 99%

“…The control of hemilability beyond equilibria situations is an attractive goal, for example, in catalysis 1. 2 One parameter to control hemilability is the redox state of the metal, which may prefer larger or smaller coordination numbers. The copper(II/I) redox pair is a prominent case in point 3.…”

Section: Introductionmentioning

confidence: 99%

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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“…The construction of supramolecular structures through metal-directed assembly represents a rapid and quantitative way of generating abiotic complexes capable of achieving selectivity and reactivity reminiscent of biological systems for many different types of chemical reactions. − Among these methods, the Weak-Link Approach (WLA) ,− ,− stands out for its ability to generate structures from hemilabile ligands that can be reversibly converted between “closed” condensed intermediates and “open” flexible structures. With proper design, these two states can exhibit dramatically different stoichiometric or catalytic reactivities, thereby allowing one to create allosteric enzyme mimics, including ones that mimic PCR target amplification and ELISA signal amplification, exhibit adjustable host–guest chemistry, and behave as switchable living-polymerization catalysts .…”

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confidence: 99%

One-Pot Synthesis of an Fe(II) Bis-Terpyridine Complex with Allosterically Regulated Electronic Properties

et al. 2012

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Herein we report the one-pot synthesis of Fe(II) bis-terpyridine complexes with two peripheral square-planar Pt(II) bis-phosphinoalkylthioether moieties. These novel structures, which exhibit allosterically controllable electronic properties, are made by taking advantage of two orthogonal and high-yielding reactions. The prototypical complex can be structurally regulated through the reversible abstraction and introduction of chloride ions to the Pt(II) centers. This moves the Fe(II) center and two Pt(II) metal centers into and out of communication with each other, causing changes in the electronic structure of the complex and its corresponding optical and redox properties. The start and end points of the allosterically regulated system have been characterized by single-crystal X-ray diffraction and NMR, UV-vis, and (57)Fe Mößbauer spectroscopy.

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Crystallographic Snapshots of the Bond‐Breaking Isomerization Reactions Involving Nickel(II) Complexes with Hemilabile Ligands

Cited by 10 publications

References 47 publications

Mapping the Binding Modes of Hemilabile Pincer–Crown Ether Ligands in Solution Using Diamagnetic Anisotropic Effects on NMR Chemical Shift

Mapping the Binding Modes of Hemilabile Pincer–Crown Ether Ligands in Solution Using Diamagnetic Anisotropic Effects on NMR Chemical Shift

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

One-Pot Synthesis of an Fe(II) Bis-Terpyridine Complex with Allosterically Regulated Electronic Properties

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