Self-Assembly of Discrete Cyclic Nanostructures Mediated by Transition Metals

▪ Abstract Proton-coupled electron transfer (PCET) is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues. We review several are...

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Proton-Coupled Electron Transfer

Dioxygen activation at mononuclear nonheme iron active sites: enzymes, models, and intermediates.

Rhodium(III)-catalyzed direct functionalization of C-H bonds under oxidative conditions leading to C-C, C-N, and C-O bond formation is reviewed. Various arene substrates bearing nitrogen and oxygen directing groups are covered in their coupling with unsaturated partners such as alkenes and alkynes. The facile construction of C-E (E = C, N, S, or O) bonds makes Rh(III) catalysis an attractive step-economic approach to value-added molecules from readily available starting materials. Comparisons and contrasts between rhodium(III) and palladium(II)-catalyzed oxidative coupling are made. The remarkable diversity of structures accessible is demonstrated with various recent examples, with a proposed mechanism for each transformation being briefly summarized (critical review, 138 references).

C–C, C–O and C–N bond formation via rhodium(III)-catalyzed oxidative C–H activation

The applications of copper (Cu) and Cu-based nanoparticles, which are based on the earth-abundant and inexpensive copper metal, have generated a great deal of interest in recent years, especially in the field of catalysis. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. In addition, the design and development of novel support and/or multimetallic systems (e.g., alloys, etc.) has also made significant contributions to the field. In this comprehensive review, we report different synthetic approaches to Cu and Cu-based nanoparticles (metallic copper, copper oxides, and hybrid copper nanostructures) and copper nanoparticles immobilized into or supported on various support materials (SiO2, magnetic support materials, etc.), along with their applications i...

http://pubs.acs.org/doi/pdfplus/10.1021/acs.chemrev.5b00482

Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis.

Structure and Spectroscopy of Copper−Dioxygen Complexes

The binuclear copper enzyme tyrosinase activates O2 to form a μ-η2:η2-peroxodicopper(II) complex, which oxidizes phenols to catechols. Here, a synthetic μ-η2:η2-peroxodicopper(II) complex, with an absorption spectrum similar to that of the enzymatic active oxidant, is reported to rapidly hydroxylate phenolates at –80°C. Upon phenolate addition at extreme temperature in solution (–120°C), a reactive intermediate consistent with a bis-μ-oxodicopper(III)-phenolate complex, with the O–O bond fully cleaved, is observed experimentally. The subsequent hydroxylation step has the hallmarks of an electrophilic aromatic substitution mechanism, similar to tyrosinase. Overall, the evidence for sequential O–O bond cleavage and C–O bond formation in this synthetic complex suggests an alternative intimate mechanism to the concerted or late stage O–O bond scission generally accepted for the phenol hydroxylation reaction performed by tyrosinase.

https://science.sciencemag.org/content/sci/308/5730/1890.full.pdf

Tyrosinase Reactivity in a Model Complex: An Alternative Hydroxylation Mechanism

Lipoxygenases are mononuclear non-heme iron enzymes that regio- and stereospecifcally convert 1,4-pentadiene subunit-containing fatty acids into alkyl peroxides. The rate-determining step is generally accepted to be hydrogen atom abstraction from the pentadiene subunit of the substrate by an active ferric hydroxide species to give a ferrous water species and an organic radical. Reported here are the synthesis and characterization of a ferric model complex, [FeIII(PY5)(OMe)](OTf)2, that reacts with organic substrates in a manner similar to the proposed enzymatic mechanism. The ligand PY5 (2,6-bis(bis(2-pyridyl)methoxymethane)pyridine) was developed to simulate the histidine-dominated coordination sphere of mammalian lipoxygenases. The overall monoanionic coordination provided by the endogenous ligands of lipoxygenase confers a strong Lewis acidic character to the active ferric site with an accordingly positive reduction potential. Incorporation of ferrous iron into PY5 and subsequent oxidation yields a sta...

T. Daniel P. Stack

Papers

Structure and Spectroscopy of Copper−Dioxygen Complexes

Tyrosinase Reactivity in a Model Complex: An Alternative Hydroxylation Mechanism

C−H Bond Activation by a Ferric Methoxide Complex: Modeling the Rate-Determining Step in the Mechanism of Lipoxygenase

Aryl CH Activation by CuII To Form an Organometallic Aryl–CuIII Species: A Novel Twist on Copper Disproportionation†

Recent advances in phenoxyl radical complexes of salen-type ligands as mixed-valent galactose oxidase models.