Copper(I)/O<sub>2</sub> Chemistry with Imidazole Containing Tripodal Tetradentate Ligands Leading to μ-1,2-Peroxo−Dicopper(II) Species

Lee, Yunho; Park, Ga Young; Lucas, Heather R.; Vajda, P.; Kamaraj, Kaliappan; Vance, Michael A.; Milligan, Ashley E.; Woertink, Julia S.; Siegler, Maxime A.; Sarjeant, Amy A.; Zakharov, Lev N.; Rheingold, Arnold L.; Solomon, Edward I.; Karlin, Kenneth D.

doi:10.1021/ic9017695

Cited by 48 publications

(71 citation statements)

References 59 publications

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“…81 The lengthening of the O–O bond is thus a consequence of an increased localization of charge density in a π (Mn–O) orbital (shown in Figure 6) that is antibonding with respect to the peroxo O–O bond. These theoretical results are supported by literature precedent 33–35,71,73–76 and agree with the bonding picture, established for Fe(III)–OOR compounds, which also includes a π (Fe–O) bond formed via overlap between a π v *(O–O) orbital and a symmetry-appropriate metal d orbital. 46,49 In both cases, the end-on η 1 -peroxo behaves as a π -donor ligand.…”

Section: Resultssupporting

confidence: 89%

Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes

et al. 2013

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Manganese–peroxos are proposed as key intermediates in a number of important biochemical and synthetic transformations. Our understanding of the structural, spectroscopic, and reactivity properties of these metastable species is limited, however, and correlations between these properties have yet to be established experimentally. Herein we report the crystallographic structures of a series of structurally related metastable Mn(III)–OOR compounds, and examine their spectroscopic and reactivity properties. The four reported Mn(III)–OOR compounds extend the number of known end-on Mn(III)–(η1-peroxos) to six. The ligand backbone is shown to alter the metal–ligand distances and modulate the electronic properties key to bonding and activation of the peroxo. The mechanism of thermal decay of these metastable species is examined via variable-temperature kinetics. Strong correlations between structural (O–O and Mn⋯Npy,quin distances), spectroscopic (E(πv*(O–O) → Mn CT band), νO–O), and kinetic (ΔH‡ and ΔS‡) parameters for these complexes provide compelling evidence for rate-limiting O–O bond cleavage. Products identified in the final reaction mixtures of Mn(III)–OOR decay are consistent with homolytic O–O bond scission. The N-heterocyclic amines and ligand backbone (Et vs Pr) are found to modulate structural and reactivity properties, and O–O bond activation is shown, both experimentally and theoretically, to track with metal ion Lewis acidity. The peroxo O–O bond is shown to gradually become more activated as the N-heterocyclic amines move closer to the metal ion causing a decrease in π-donation from the peroxo πv*(O–O) orbital. The reported work represents one of very few examples of experimentally verified relationships between structure and function.

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Section: Resultssupporting

confidence: 89%

Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes

et al. 2013

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“…2d). 59–63 The g ⊥ (2.20), g || (2.00), A ⊥ (87 G), and A || (83 G) values are comparable to those of the previously reported Cu(II) complexes with a trigonal-bipyramidal geometry.…”

Section: Resultssupporting

confidence: 85%

Spectroscopic and computational characterization of CuII–OOR (R = H or cumyl) complexes bearing a Me6-tren ligand

et al. 2011

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A copper(II)–hydroperoxo complex, [Cu(Me6-tren)(OOH)]+ (2), and a copper(II)–cumylperoxo complex, [Cu(Me6-tren)(OOC(CH3)2Ph)]+ (3), were synthesized by reacting [Cu(Me6-tren)(CH3CN)]2+ (1) with H2O2 and cumyl-OOH, respectively, in the presence of triethylamine. These intermediates, 2 and 3, were successfully characterized by various physicochemical methods such as UV-vis, ESI-MS, resonance Raman and EPR spectroscopies, leading us to propose structures of the Cu(II)–OOR species with a trigonal-bipyramidal geometry. Density functional theory (DFT) calculations provided geometric and electronic configurations of 2 and 3, showing trigonal bipyramidal copper(II)–OOR geometries. These copper(II)–hydroperoxo and –cumylperoxo complexes were inactive in electrophilic and nucleophilic oxidation reactions.

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“…Most of these complexes are supported by chelating or multi-nucleating ligands bearing amine, pyridine, benzimidazole or pyrazole groups. Exclusive use of the imidazole moiety observed in biology is very limited in this field, especially with unprotected imidazole N-H bonds 13,14,25 .Investigation of the oxidizing ability of synthetic Cu-O 2 systems formed with monodentate nitrogen-based ligands to reproduce the reactivity of Tyr is a research area that has so far spanned more than half a century. Brackman and Havinga first demonstrated phenol hydroxylation to o-quinone with copper-morpholine complexes and dioxygen in 1955 (ref.…”

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confidence: 99%

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confidence: 99%

Self-assembly of the oxy-tyrosinase core and the fundamental components of phenolic hydroxylation

et al. 2012

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The enzyme tyrosinase contains two Cu(I) centres, trigonally coordinated by imidazole nitrogens of six conserved histidine residues. The enzyme activates O(2) to form a µ-η(2):η(2)-peroxo-dicopper(II) core, which hydroxylates tyrosine to a catechol in the first committed step of melanin biosynthesis. Here, we report a family of synthetic peroxo complexes, with spectroscopic and chemical features consistent with those of oxygenated tyrosinase, formed through the self-assembly of monodentate imidazole ligands, Cu(I) and O(2) at -125 °C. An extensively studied complex reproduces the enzymatic electrophilic oxidation of exogenous phenolic substrates to catechols in good stoichiometric yields. The self-assembly and subsequent reactivity support the intrinsic stability of the Cu(2)O(2) core with imidazole ligation, in the absence of a polypeptide framework, and the innate capacity to effect hydroxylation of phenolic substrates. These observations suggest that a foundational role of the protein matrix is to facilitate expression of properties native to the core by bearing the entropic costs of assembly and precluding undesired oxidative degradation pathways.

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Copper(I)/O₂ Chemistry with Imidazole Containing Tripodal Tetradentate Ligands Leading to μ-1,2-Peroxo−Dicopper(II) Species

Cited by 48 publications

References 59 publications

Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes

Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes

Spectroscopic and computational characterization of CuII–OOR (R = H or cumyl) complexes bearing a Me6-tren ligand

Self-assembly of the oxy-tyrosinase core and the fundamental components of phenolic hydroxylation

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Copper(I)/O2 Chemistry with Imidazole Containing Tripodal Tetradentate Ligands Leading to μ-1,2-Peroxo−Dicopper(II) Species

Cited by 48 publications

References 59 publications

Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes

Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes

Spectroscopic and computational characterization of CuII–OOR (R = H or cumyl) complexes bearing a Me6-tren ligand

Self-assembly of the oxy-tyrosinase core and the fundamental components of phenolic hydroxylation

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Copper(I)/O₂ Chemistry with Imidazole Containing Tripodal Tetradentate Ligands Leading to μ-1,2-Peroxo−Dicopper(II) Species