Single and double deprotonation/dearomatization of the N,S-donor pyridinophane ligand in ruthenium complexes

We report a series of ruthenium complexes with a tetradentate N,S-donor ligand, 2,11-dithia[3.3](2,6)pyridinophane (N2S2), that undergo single and double deprotonation in the presence of a base leading to the deprotonation of one or both pyridine rings. Both singly and doubly deprotonated complexes were structurally characterized by single-crystal X-ray diffraction. The NMR spectra are indicative of the dearomatization of one or both pyridine rings upon the deprotonation of the CH2–S arm, similar to the dearomatization of phosphine-containing pincer ligands. The deprotonated (N2S2)Ru complexes did not show appreciable catalytic or stoichiometric reactivity in transfer hydrogenation, hydrogenation and dehydrogenation of alcohols, and attempted activation of H2, CO2, and other substrates. Such a lack of reactivity is likely due to the low stability of the deprotonated species as evident from the structural characterization of one of the decomposition products in which shrinkage of the macrocyclic ring occurs via picolyl arm migration.journal articl

Light-Driven Purification of Progesterone from Steroid Mixtures Using a Photoresponsive Metal-Organic Capsule.

Publication status: PublishedChemical separations are expensive, consuming 10-15% of humanity's global energy budget. Many current separation methods employ thermal energy for distillation, often through the combustion of carbon-containing fuels, or extractions and crystallizations from organic solvents, which must then be discarded or redistilled, with a substantial energetic cost. The direct use of renewable energy sources, such as light, could enable the development of novel separations processes, as is required for the transition away from fossil fuel use. Metal-organic capsules, which can selectively bind molecules from mixtures, can provide the foundation for these novel separations processes. Here we report a tetrahedral metal-organic capsule bearing light-responsive diazo moieties around its metal-ion vertices. This capsule can be used to selectively separate progesterone from a mixture of steroids in a process driven by visible light energy. Our process combines biphasic extraction and selective binding of progesterone with the light-driven release of this molecule in purified form. Ultimately, our process might be adapted to the purifications of the many other fine chemical products that are bound selectively by capsules

A complex comprising a cyanine dye rotaxane and a porphyrin nanoring as a model light‐harvesting system

A nanoring‐rotaxane supramolecular assembly with a Cy7 cyanine dye (hexamethylindotricarbocyanine) threaded along the axis of the nanoring was synthesized as a model for the energy transfer between the light‐harvesting complex LH1 and the reaction center in purple bacteria photosynthesis. The complex displays efficient energy transfer from the central cyanine dye to the surrounding zinc porphyrin nanoring. We present a theoretical model that reproduces the absorption spectrum of the nanoring and quantifies the excitonic coupling between the nanoring and the central dye, thereby explaining the efficient energy transfer and demonstrating similarity with structurally related natural light‐harvesting systems

Imaging Electrode Heterogeneity Using Chemically Confined Fluorescence Electrochemical Microscopy

By varying the total and the relative concentrations of a strong acid (HClO₄) and a pH-sensitive fluorescent dye (8-hydroxypyrene-1,3,6-trisulfonate), this work demonstrates that both the hydrogen evolution reaction or the oxygen reduction reaction can be selectively and optically studied at an electrochemical interface. The local pH shift driven by the redox reaction can be visualized through fluorescence imaging of the interface. The use of finite strong acid concentrations further serves to constrain the pH change to a thin layer adjacent to the surface. This chemical confinement of the fluorophore improves the system’s resolution and enables micrometer scale heterogeneity on the electrode surface to be readily visualized

Single and double deprotonation/dearomatization of the N,S-donor pyridinophane ligand in ruthenium complexes

We report a series of ruthenium complexes with a tetradentate N,S-donor ligand, 2,11-dithia[3.3](2,6)pyridinophane (N2S2), that undergo single and double deprotonation in the presence of a base leading to the deprotonation of one or both pyridine rings. Both singly and doubly deprotonated complexes were structurally characterized by single-crystal X-ray diffraction. The NMR spectra are indicative of the dearomatization of one or both pyridine rings upon the deprotonation of the CH2–S arm, similar to the dearomatization of phosphine-containing pincer ligands. The deprotonated (N2S2)Ru complexes did not show appreciable catalytic or stoichiometric reactivity in transfer hydrogenation, hydrogenation and dehydrogenation of alcohols, and attempted activation of H2, CO2, and other substrates. Such a lack of reactivity is likely due to the low stability of the deprotonated species as evident from the structural characterization of one of the decomposition products in which shrinkage of the macrocyclic ring occurs via picolyl arm migration

Coupled Optical and Electrochemical Probing of Silver Nanoparticle Destruction in a Reaction Layer

The oxidation of silver nanoparticles is induced to occur near to, but not at, an electrode surface. This reaction at a distance from the electrode is studied through the use of dark-field microscopy, allowing individual nanoparticles and their reaction with the electrode product to be visualized. The oxidation product diffuses away from the electrode and oxidizes the nanoparticles in a reaction layer, resulting in their destruction. The kinetics of the silver nanoparticle solution-phase reaction is shown to control the length scale over which the nanoparticles react. In general, the new methodology offers a route by which nanoparticle reactivity can be studied close to an electrode surface