Molecular p-dopants designed to undergo electron transfer with organic semiconductors are typically planar molecules with high electron affinity. However, their planarity can promote the formation of ground-state charge transfer complexes with the semiconductor host and results in fractional instead of integer charge transfer, which is highly detrimental to doping efficiency. Here, we show this process can be readily overcome by targeted dopant design exploiting steric hindrance. To this end, we synthesize and characterize the remarkably stable p-dopant 2,2',2''-(cyclopropane-1,2,3-triylidene)tris(2-(perfluorophenyl)acetonitrile) comprising pendant functional groups that sterically shield its central core while retaining high electron affinity. Finally, we demonstrate it outperforms a planar dopant of identical electron affinity and increases the thin film conductivity by up to an order of magnitude. We believe exploiting steric hindrance represents a promising design strategy towards molecular dopants of enhanced doping efficiency.

Primary hydroxylamines, RNHOH, decompose readily in the presence of transition metal ions. We show that this reactivity can be arrested by ligand design via an intramolecular hydrogen bond. Six metal complexes with an intact NHOH group were synthesized and crystallographically characterized. The Cu-hydroxylamine complexes can catalyze the aerobic oxidation of benzylic alcohols.

A series of copper/nitrosoarene complexes was created that mimics several steps in biomimetic O2 activation by copper(I). The reaction of the copper(I) complex of N,N,N',N'-tetramethypropylenediamine with a series of para-substituted nitrosobenzene derivatives leads to adducts in which the nitrosoarene (ArNO) is reduced by zero, one, or two electrons, akin to the isovalent species dioxygen, superoxide, and peroxide, respectively. The geometric and electronic structures of these adducts were characterized by means of X-ray diffraction, vibrational analysis, ultraviolet-visible spectroscopy, NMR, electrochemistry, and density functional theory (DFT) calculations. The bonding mode of the NO moiety depends on the oxidation state of the ArNO moiety: κN for ArNO, mononuclear η2-NO and dinuclear μ-η2:η1 for ArNO•-, and dinuclear μ-η2:η2 for ArNO2-. 15N isotopic labeling confirms the reduction state by measuring the NO stretching frequency (1392 cm-1 for κN-ArNO, 1226 cm-1 for η2-ArNO•-, 1133 cm-1 for dinuclear μ-η2:η1-ArNO•-, and 875 cm-1 for dinuclear μ-η2:η2 for ArNO2-). The 15N NMR signal disappears for the ArNO•- species, establishing a unique diagnostic for the radical state. Electrochemical studies indicate reduction waves that are consistent with one-electron reduction of the adducts and are compared with studies performed on Cu-O2 analogues. DFT calculations were undertaken to confirm our experimental findings, notably to establish the nature of the charge-transfer transitions responsible for the intense green color of the complexes. In fine, this family of complexes is unique in that it walks through three redox states of the ArNO moiety while keeping the metal and its supporting ligand the same. This work provides snapshots of the reactivity of the toxic nitrosoarene molecules with the biologically relevant Cu(I) ion.

Bismuth metallic nanoparticles have evoked considerable interest in catalysis owing to their small size, high surface area-to-volume ratio, and low toxicity. However, the need for toxic reductants and organic solvents in their synthesis often limits their desirability for application development. Here, we describe a green strategy to synthesize bismuth nanodots via the redox reactions between bismuth nitrate and d-glucose, in the presence of poly(vinylpyrrolidone) in the basic aqueous phase. Both reagents play a crucial role in the formation of monodisperse bismuth nanodots acting as mild reducing and capping agents, respectively. We further demonstrate that the catalytic activity of these dots via the successful reduction of the environmental contaminant 4-nitrophenol to its useful 4-aminophenol analogue requiring only 36 μg/mL nanocatalyst for 20 mM of the substrate. Moreover, they can be recovered and recycled in multiple reactions before the onset of an appreciable loss of catalytic activity. The proposed facile synthetic route and inexpensive matrix materials lead the way to access bismuth nanodots for both the fundamental study of reactions and their industrial catalysis applications.

The double crossover junction (DX) is a fundamental building block for generating complex and varied structures from DNA. However, its implementation in functional devices is limited to the inherent properties of DNA itself. Here, we developed design strategies to generate the first metal-DX DNA tiles (DXM) by site-specifically functionalizing the tile crossovers with tetrahedral binding pockets that coordinate Cu-I. These DX junctions bind two Cu-I ions independently at distinct sites, display greater thermal stability than native DX tiles upon metalation, and melt in a cooperative fashion. In addition, the right-handed helical chirality of DNA is transferred to the metal centers. Our tiles display high metal ion selectivity, such that Cu-II is spontaneously reduced to Cu-I in situ. By modifying our design over three generations of tiles, we elucidated the thermodynamic and geometric requirements for the successful assembly of DXM tiles, which have direct applicability in developing robust, stable DNA-based materials with electroactive, photoactive, and catalytic properties.

Herein we present a new strategy to achieve chiral induction and redox switching along the backbone of metallohelicate architectures, wherein a DNA duplex directs the handedness and charge transport properties of a metal-organic assembly more than 60 bonds away (a distance of >10 nm). The quantitative and site-specific binding of copper(i) ions to DNA-templated coordination sites imparts enhanced thermodynamic stability to the assembly, while the DNA duplex transfers its natural right-handed helicity to the proximal and distal metal centers of the helicates. When copper(ii) ions are employed instead of copper(i) ions, spontaneous DNA-mediated reduction occurs, which we propose is followed by a slower change in coordination environment (from pentacoordinate Cu-II to tetrahedral Cu-I) to generate copper(i) helicates. We demonstrate that the reduction of the adjacent and distal bis-phenanthroline sites is dependent on their proximity to DNA guanine bases (which act as the electron source). The kinetics of helical charge transport can thus be tuned based on guanine-Cu-II separation, resulting in a sequence- and distance-dependent redox switch that transfers electronic information from DNA to multiple linearly-arranged metal centers.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The topology and degree of electron transfer in self-assembled redox reactions between copper(i) species and nitrosoarenes are controlled by ligand properties.

1,2-Bis(N-benzoyl-N-methylamino) benzene (2) forms centrosymmetric hydrate crystals (2 center dot xH(2)O) and non-centrosymmetric anhydrous crystals. Dehydration of this hydrate (30 min at 140 degrees C) resulted in the formation of chiral crystals (i.e. a physical racemate of the conglomerate crystals) as verified using solid-state circular dichroism and powder X-ray diffraction. Subsequent attrition-enhanced deracemization, also known as Viedma ripening, was used to obtain homochiral crystals of 2 within 5 h.

Nitrogen-containing heterocycles are fundamentally important to the function of pharmaceuticals, agrochemicals and materials. Herein, we report a bio-inspired approach to the synthesis of oxindoles, which couples the energetic requirements of dehydrogenative C-N bond formation to the reduction of molecular oxygen (O-2). Our method is inspired by the biosynthesis of melanin pigments (melanogenesis), but diverges from the biosynthetic polymerization. Mechanistic analysis reveals the involvement of Cu-II-semiquinone radical intermediates, which enable dehydrogenative carbon-heteroatom bond formation that avoids a catechol/quinone redox couple. This mitagates the deleterious polarity reversal that results from phenolic dearomatization, and enables a high-yielding phenolic C-H functionalization under catalytic aerobic conditions. Our work highlights the broad synthetic utility and efficiency of forming C-N bonds via a catalytic aerobic dearomatization of phenols, which is currently an underdeveloped transformation.

Phenols are abundant feedstock chemicals and their functionalization constitutes an attractive method for the synthesis of fine chemicals and materials. In biological systems, the copper-containing enzyme tyrosinase catalyzes the ortho-oxygenation of tyrosine into L-dopaquinone in the first step of the melanogenesis process. The copper centres in the enzyme activate O2 through the formation of μ-η2:η2-peroxodicopper(II) (SP) and subsequent electrophilic aromatic substitution on tyrosine provides L-dopaquinone. Despite many efforts for the past 50 years to develop a synthetic mimic for the aerobic oxygenation of phenols, a truly catalytic system for the selective ortho-oxygenation of phenols was only recently reported. The copper(I) complex of N,N’-di-tert-butylethylenediamine (DBED) is used as the precatalyst that activates oxygen and catalyzes the ortho-oxygenation of phenols. Investigating the mechanism of this catalytic process is the first objective of this research, whereby spectroscopic techniques are used to identify intermediates in this reaction and perform kinetic studies. The second objective of the research is the development of analogous phenol ortho-amination using nitrosoarenes as substitutes for oxygen. The mechanistic studies were performed by spectroscopic characterization of intermediates and comparison with independently prepared complexes or literature spectra. In situ UV-vis spectroscopy of the reaction at 25 oC demonstrated the formation of a copper(II)-semiquinone complex that persists during the oxygenation process. In order to identify the preceding intermediates, UV-vis spectroscopy at temperatures as low as -120 oC was used, and the intermediates were characterized spectroscopically through comparison with similar reported species. Based on the observed intermediates a mechanism is proposed whereby the copper complex activates oxygen to forming SP; an oxygen atom is then transferred to a bound phenolate through electrophilic aromatic substitution. Kinetic studies using low-temperature stopped-flow techniques provides evidence for a binuclear mechanism of O2 activation and that the reaction rate is independent on phenol concentration. The mechanistic investigation suggests that oxygen activation and phenol functionalization proceed through the same pathway as the one observed with tyrosinase, thus substantiating the bio-mimetic nature of this catalytic reaction. Nitrosoarenes (ArNO) are isoelectronic with singlet oxygen, therefore copper-ArNO complexes are structural and electronic mimics of copper-O2 complexes, and are expected to react in a similar way with external substrates. The redox lability of nitrosoarenes was proved by preparing and characterizing a copper(II)-nitrosoarene radical-anion complex. Structural and computational investigation confirmed its similarity to end-on copper(II)-superoxo species. Two-electron reduction of nitrosoarene was performed using the copper(I) complex of diamine ligand, and results in a complex that mimics the side-on copper(II)-peroxo (SP) structure. This complex undergoes stoichiometric reaction with phenolates to form aminophenols after reductive work-up, thus demonstrating similar reactivity to tyrosinase models.

Controlling product selectivity during the catalytic aerobic oxidation of phenols remains a significant challenge that hinders reaction development. This work provides a mechanistic picture of a Cu-catalyzed, aerobic functionalization of phenols that is selective for phenoxy-coupled ortho-quinones. We show that the immediate product of the reaction is a Cu(II)-semiquinone radical complex and reveal that ortho-oxygenation precedes oxidative coupling. This complex is the resting state of the Cu catalyst during turnover at room temperature. A mechanistic study of the formation of this complex at low temperatures demonstrates that the oxygenation pathway mimics the dinuclear Cu enzyme tyrosinase by involving a dinuclear side-on peroxodicopper(II) oxidant. Unlike the enzyme, however, the rate-limiting step of the ortho-oxygenation reaction is the self-assembly of the oxidant from Cu(I) and O2. We provide details for all steps in the cycle and demonstrate that turnover is contingent upon proton-transfer events that are mediated by a slight excess of ligand. Finally, our knowledge of the reaction mechanism can be leveraged to diversify the reaction outcome. Thus, uncoupled ortho-quinones are favored in polar, coordinating media, highlighting unusually high levels of chemoselectivity for a catalytic aerobic oxidation of a phenol.

A range of air-stable copper species was examined for catalytic activity in the catalytic aerobic transformation of phenols into ortho-quinones. Efficient catalysis was obtained with commercially available copper(II) acetate. The stability of all constituents before mixing makes for a practical process that advances previously reported copper(I)-based oxygenations.

The reaction between p-nitrosonitrobenzene and the tetramethylpropylenediamine-copper(i) complex yields a dinuclear complex that is structurally and electronically similar to side-on peroxo species known in Cu/O2 chemistry. The complex reacts with di-tert-butylphenolate via nitrene transfer, as observed through an intermediate and the aminophenol product obtained upon reductive work-up.

An unsymmetric ligand bearing a salicylimine side and a 2-nitrobenzenesufonamide side has been synthesized in two simple steps. Complexations with Cu(II), Fe(III) and Co(II) - which oxidizes to Co(III) once complexed - indicate that the ligand can be either bidentate or tridentate depending on the geometric preferences of the metal ion and whether the sulfonamide is deprotonated. The obtained crystal structures are also stabilized via hydrogen bonds and pi-pi stacking interactions. Crown Copyright (c) 2013 Published by Elsevier B.V. All rights reserved.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Substitution on the aromatic bridge of a nickel(II) salophen complex with electron-donating dimethylamino substituents creates a ligand with three stable, easily and reversibly accessible oxidation states. The one-electron-oxidized product is characterized as a nickel(II) radical complex with the radical bore by the central substituted aromatic ring, in contrast to other nickel(II) salen or salophen complexes that oxidize on the phenolate moieties. The doubly oxidized product, a singlet species, is best described as having an iminobenzoquinone bridge with a vinylogous distribution of bond lengths between the dimethylamino substituents. Protonation of the dimethylamino substituents inhibits these redox processes on the time scale of cyclovoltammetry, but electrolysis and chemical oxidation are consistent with deprotonation occurring concomitantly with electron transfer to yield the mono- and dioxidized species described above.