The First Structural Characterization of an Azoaromatic Radical Anion Stabilized by Dicopper(I) Coordination

Doslik, Nataša; Sixt, Torsten; Kaim, Wolfgang

doi:10.1002/(sici)1521-3773(19980918)37:17<2403::aid-anie2403>3.0.co;2-j

Cited by 64 publications

(14 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus, the emerging trend of utilizing “redox-active” or “noninnocent” ligand-derived transition-metal complexes has been expanding at a faster rate primarily because of their multielectron storage capacity . In this regard, metal complexes of azoheteroarenes have played an important role as redox equivalents in catalysis, molecular materials, and formation of bis-stable complexes , besides their fundamental electron-transfer aspects . Although 2,2′-azobis(pyridine) (abpy) and its analogues are well-illustrated with varying metal precursors and hold a privileged position in the library of redox-noninnocent ligands, the fascinating redox features of its structurally modified form, i.e., azobis(benzazole), have recently been divulged, which in effect emphasizes its further exploration.…”

Section: Introductionmentioning

confidence: 99%

“…In this regard, metal complexes of azoheteroarenes have played an important role as redox equivalents in catalysis, molecular materials, and formation of bis-stable complexes , besides their fundamental electron-transfer aspects . Although 2,2′-azobis(pyridine) (abpy) and its analogues are well-illustrated with varying metal precursors and hold a privileged position in the library of redox-noninnocent ligands, the fascinating redox features of its structurally modified form, i.e., azobis(benzazole), have recently been divulged, which in effect emphasizes its further exploration. Contextually, an unprecedented valence tautomerism of azobis(benzothiazole) [abbt, an analogue of azobis(benzazole)] in a {Ru(acac) 2 } (acac = acetylacetonate)-coordinated dinuclear framework had recently been depicted in the direction of molecular bis-stability for an azo-based system .…”

Section: Introductionmentioning

confidence: 99%

“…Stabilization of the radical anionic form of the azo group (−NN−) •– either by a MLCT-induced process with electronically rich low-valent metal ions or by use of an external reducing agent is well documented. The present report, however, demonstrates the unusual stabilization of (−NN−) •– in a mononuclear setup even upon coordination to an electron-poor metal via the effective role of the polar protic solvent.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Radical versus Nonradical States of Azobis(benzothiazole) as a Function of Ancillary Ligands on Selective Ruthenium Platforms

et al. 2021

View full text Add to dashboard Cite

The paper deals with the electronic impact of ancillary ligands on the varying redox features of azobis(benzothiazole) (abbt) in the newly introduced mononuclear ruthenium complexes [Ru(pap) 2 (abbt)] n (1 n ) and [Ru(bpy) 2 (abbt)] n (2 n ), where pap = 2phenylazopyridine and bpy = 2,2′-bipyridine. In this regard, the complexes [Ru II (pap) 2 (abbt •− )]ClO 4 ([1]ClO 4 ), [Ru II (pap) 2 (abbt 0 )](ClO 4 ) 2 ([1](ClO 4 ) 2 ), [Ru II (bpy) 2 (abbt 0 )](ClO 4 ) 2 ([2](ClO 4 ) 2 ), and [Ru II (bpy) 2 (abbt •− )]ClO 4 ([2]ClO 4 ) were structurally and spectroscopically characterized. Unambiguous assignments of the aforestated radical and nonradical forms of abbt in 1 + /2 + and 1 2+ /2 2+ , respectively, were made primarily based on their redox-sensitive azo (NN) bond distances as well as by their characteristic electron paramagnetic resonance (EPR)/NMR signatures. Although the radical form of abbt •− was isolated as an exclusive product in the case of strongly π-acidic pap-derived 1 + , the corresponding moderately π-acidic bpy ancillary ligand primarily delivered an oxidized form of abbt 0 in 2 2+ , along with the radical form in 2 + as a minor (<10%) component. The oxidized abbt 0 -derived [1](ClO 4 ) 2 was, however, obtained via the chemical oxidation of [1]ClO 4 . Both 1 + and 2 2+ displayed multiple closed by reversible redox processes (one oxidation O1 and four successive reductions R1−R4) within the potential window of ±2.0 V versus saturated calomel electrode. The involvement of metal-, ligand-, or metal/ligand-based frontier molecular orbitals along the redox chain was assigned based on the combined experimental (structure, EPR, and spectroelectrochemisry) and theoretical [density functional theory (DFT): molecular orbitals, Mulliken spin densities/time-dependent DFT] investigations. It revealed primarily ligand (abbt/pap or bpy)-based redox activities, keeping the metal ion as a simple spectator. Moreover, frontier molecular orbital analysis corroborated the initial isolation of the radical and nonradical species for the pap-derived 1 + and bpy-derived 2 2+ as well as facile reduction of pap and abbt in 1 + and 2 + , respectively.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Radical versus Nonradical States of Azobis(benzothiazole) as a Function of Ancillary Ligands on Selective Ruthenium Platforms

et al. 2021

View full text Add to dashboard Cite

show abstract

“…Such species are often short-lived, and on the basis of their stability they can be classified as transient, persistent, and stable radicals . Coordinated azoaromatic ligands have been found to behave as endogenous precursors to afford azo anion radical complexes in the crystalline state since the late 1990s due to the presence of a low-lying π* orbital . Subsequently, a number of azo anion radical complexes have been explored .…”

Section: Introductionmentioning

confidence: 99%

Ambient-Stable Bis-Azoaromatic-Centered Diradical [(L^•)M(L^•)] Complexes of Rh(III): Synthesis, Structure, Redox, and Spin–Spin Interaction

et al. 2017

View full text Add to dashboard Cite

Bis-azoaromatic electron traps, viz. 2-(2-pyridylazo)azoarene 1, have been synthesized by colligating electron-deficient pyridine and azoarene moieties, and they act as apposite proradical templates for the formation of stable open-shell diradical complexes [(1)Rh(1)] ([2]), starting from the low-valent electron reservoir [Rh]. The less stable monoradical [Rh(1)Cl(PPh)] (3) has also been isolated as a minor product. These π-radical complexes are multiredox systems, and the electron transfer processes occur exclusively within the pincer-type NNN ligand backbone 1. Molecular and electronic structures of the diradicals and monoradicals have been ascertained with the aid of X-ray diffraction, electrochemical, spectroelectrochemical, and spectral (electronic, IR, NMR, and EPR) studies. In the diradicals [2], the orthogonal disposition of two ligand π orbitals linked via a closed-shell metal center (t) impedes significant coupling between the radicals. Indeed, the observed magnetic moment of [2a] lies near ∼2.3 μ over the temperature range 50-300 K. A very weak antiferromagnetic (AF) intramolecular spin-spin interaction between two ligand π arrays in [(1)Rh(1)] have been found experimentally (J ≈ -5 cm), and this is further substantiated by density functional theory (DFT) calculations at the (U)B3LYP/6-31G(d,p) level.

show abstract

“…While other azo-containing ligands such as pap (phenylazopyridine) and azobispyridine have been extensively studied in coordination chemistry as redox-active bridging ligands, − azocarboxamides, a special class of azo-containing ligands, have rarely been used in coordination chemistry and for the study of redox as well as catalytic properties. A recent report on ruthenium azocarboxamide half-sandwich complexes from our group illustrated the redox-triggered change in the chelating binding pocket and the electronic properties of the complexes .…”

Section: Introductionmentioning

confidence: 96%

Iridium Azocarboxamide Complexes: Variable Coordination Modes, C–H Activation, Transfer Hydrogenation Catalysis, and Mechanistic Insights

et al. 2021

View full text Add to dashboard Cite

Azocarboxamides, a special class of azo ligands, display intriguing electronic properties due to their versatile binding modes and coordination flexibility. These properties may have significant implications for their use in homogeneous catalysis. In the present report, halfsandwich Ir−Cp* complexes of two different azocarboxamide ligands are presented. Different coordination motifs of the ligand were realized using base and chloride abstracting ligand to give N ∧ N-, N ∧ O-, and N ∧ C-chelated monomeric iridium complexes. For the azocarboxamide ligand having methoxy substituted at the phenyl ring, a mixture of N ∧ C-chelated mononuclear (Ir-5) and N ∧ N,N ∧ C-chelated dinuclear complexes (Ir-4) were obtained by activating the C−H bond of the aryl ring. No such C−H activation was observed for the ligand without the methoxy substituent. The molecular identity of the complexes was confirmed by spectroscopic analyses, while X-ray diffraction analyses further confirmed three-legged piano-stool structure of the complexes along with the above binding modes. All complexes were found to exhibit remarkable activity as precatalysts for the transfer hydrogenation of carbonyl groups in the presence of a base, even at low catalyst loading. Optimization of reaction conditions divulged superior catalytic activity of Ir-3 and Ir-4 complexes in transfer hydrogenation over the other catalysts. Investigation of the influence of binding modes on the catalytic activity along with wide range substrates, tolerance to functional groups, and mechanistic insights into the reaction pathway are also presented. These are the first examples of C−H activation in azocarboxamide ligands.

show abstract

The First Structural Characterization of an Azoaromatic Radical Anion Stabilized by Dicopper(I) Coordination

Abstract: Double chelate coordination of [Cu(Ph P) ] stabilizes the radical anion of 2,2'-azobis(5-chloropyrimidine), which exhibits a N-N bond length of 1.345(7) Å in the complex (see picture). This is consistent with a one-electron reduced azo functionality.

Cited by 64 publications

References 0 publications

Radical versus Nonradical States of Azobis(benzothiazole) as a Function of Ancillary Ligands on Selective Ruthenium Platforms

Radical versus Nonradical States of Azobis(benzothiazole) as a Function of Ancillary Ligands on Selective Ruthenium Platforms

Ambient-Stable Bis-Azoaromatic-Centered Diradical [(L^•)M(L^•)] Complexes of Rh(III): Synthesis, Structure, Redox, and Spin–Spin Interaction

Iridium Azocarboxamide Complexes: Variable Coordination Modes, C–H Activation, Transfer Hydrogenation Catalysis, and Mechanistic Insights

Contact Info

Product

Resources

About

The First Structural Characterization of an Azoaromatic Radical Anion Stabilized by Dicopper(I) Coordination

Abstract: Double chelate coordination of [Cu(Ph P) ] stabilizes the radical anion of 2,2'-azobis(5-chloropyrimidine), which exhibits a N-N bond length of 1.345(7) Å in the complex (see picture). This is consistent with a one-electron reduced azo functionality.

Cited by 64 publications

References 0 publications

Radical versus Nonradical States of Azobis(benzothiazole) as a Function of Ancillary Ligands on Selective Ruthenium Platforms

Radical versus Nonradical States of Azobis(benzothiazole) as a Function of Ancillary Ligands on Selective Ruthenium Platforms

Ambient-Stable Bis-Azoaromatic-Centered Diradical [(L•)M(L•)] Complexes of Rh(III): Synthesis, Structure, Redox, and Spin–Spin Interaction

Iridium Azocarboxamide Complexes: Variable Coordination Modes, C–H Activation, Transfer Hydrogenation Catalysis, and Mechanistic Insights

Contact Info

Product

Resources

About

Ambient-Stable Bis-Azoaromatic-Centered Diradical [(L^•)M(L^•)] Complexes of Rh(III): Synthesis, Structure, Redox, and Spin–Spin Interaction