Accessing Unusual Reactivity through Chelation-Promoted Bond Weakening.

Highly reducing Sm(II) reductants and protic ligands were used as a platform to ascertain the relationship between low-valent metal-protic ligand affinity and degree of ligand X-H bond weakening with the goal of forming potent proton-coupled electron transfer (PCET) reductants. Among the Sm(II)-protic ligand reductant systems investigated, the samarium dibromide -methylethanolamine (SmBr-NMEA) reagent system displayed the best combination of metal-ligand affinity and stability against H evolution. The use of SmBr-NMEA afforded the reduction of a range of substrates that are typically recalcitrant to single-electron reduction including alkynes, lactones, and arenes as stable as biphenyl.

Contrasting Effect of Additives on Photoinduced Reactions of SmI.

The work described herein compares the effect of additives (HMPA, methanol, ethylene glycol, pinacol, N-methylethanolamine) on thermal and photochemical reactions of samarium diiodide (SmI ). In thermal reactions, additives that coordinate to SmI induce a significant increase in reaction rate. In photochemical reactions, the presence of an electronegative atom with a highly localized negative charge on the substrate leads to a rate deceleration.

Mechanistic Study and Development of Catalytic Reactions of Sm(II).

Samarium diiodide (SmI) is one of the most widely used single-electron reductants available to organic chemists because it is effective in reducing and coupling a wide range of functional groups. Despite the broad utility and application of SmI in synthesis, the reagent is used in stoichiometric amounts and has a high molecular weight, resulting in a large amount of material being used for reactions requiring one or more equivalents of electrons. Although few approaches to develop catalytic reactions have been designed, they are not widely used or require specialized conditions.

Task-Dependent Coordination Levels of SmI.

Ligation plays a multifaceted role in the chemistry of SmI. Depending on the ligand, two of its major effects are increasing the reduction potential of SmI, and in the case of a ligand, which is also a proton donor, it may also enhance the reaction by protonation of the radical anion generated in the preceding step. It turns out that the number of ligand molecules that are needed to maximize the reduction potential of SmI is significantly smaller than the number of ligand molecules needed for a maximal enhancement of the protonation rate.

Aza versus Oxophilicity of SmI : A Break of a Paradigm.

Ligands that coordinate to SmI through oxygen are prevalent in the literature and make up a significant portion of additives employed with the reagent to perform reactions of great synthetic importance. In the present work a series of spectroscopic, calorimetric and kinetic studies demonstrate that nitrogen-based analogues of many common additives have a significantly higher affinity for Sm than the oxygen-based counterparts. In addition, electrochemical experiments show that nitrogen-based ligands significantly enhance the reducing power of SmI .

Deciphering a 20-Year-Old Conundrum: The Mechanisms of Reduction by the Water/Amine/SmI2 Mixture.

The reaction of SmI2 with the substrates 3-methyl-2-butanone, benzyl chloride, p-cyanobenzyl chloride, and anthracene were studied in the presence of water and an amine. In all cases, the water content versus rate profile shows a maximum at around 0.2 M H2 O.

Rate and mechanistic investigation of Eu(OTf)₂-mediated reduction of graphene oxide at room temperature.

We describe a fast, efficient, and mild approach to prepare chemically reduced graphene oxide (rGO) at room temperature using divalent europium triflate {Eu(OTf)2}. The characterization of solution-processable reduced graphene oxide has been carried out by various spectroscopic (FT-IR, UV-visible absorption, and Raman), microscopic (TEM and AFM), and powder X-ray diffraction (XRD) techniques. Kinetic study indicates that the bimolecular rate constants for the reduction of graphene oxide are 13.

Supramolecular design for two-component hydrogels with intrinsic emission in the visible region.

We report, for the first time, an in situ formation of two-component hydrogels from pyridine derivatives of poly(aryl ether) dendrons and tartaric acid. The two-component system (dendron + acid) undergoes J-type aggregation, leading to fibrillar type self-assembly in THF-water mixture along with blue (470 nm) and green (500 nm) intrinsic emissions.

Effect of crown ethers on the ground and excited state reactivity of samarium diiodide in acetonitrile.

Electron transfer from the ground and excited states of Sm[15-crown-5](2)I(2) complex to a series of electron acceptors (benzaldehyde, acetophenone, benzophenone, nitrobenzene, benzyl bromide, benzyl chloride, 1-iodohexane, and 1,4-dinitrobenzene) was investigated in acetonitrile. Electron transfer from the ground state of the Sm(II)-crown system to aldehydes and ketones has a significant inner sphere component indicating that the oxophilic nature of Sm(II) prevails in the system even in the presence of bulky ligands such as 15-crown-5 ether. Activation parameters for the ground state electron transfer were determined, and the values were consistent with the proposed mechanistic models.