Outer-Sphere Electrophilic Fluorination of Organometallic Complexes

Organofluorine chemistry plays a key role in materials science, pharmaceuticals, agrochemicals, and medical imaging. However, the formation of new carbon–fluorine bonds with controlled regiochemistry and functional group tolerance is synthetically challenging. The use of metal complexes to promote fluorination reactions is of great current interest, but even state-of-the-art approaches are limited in their substrate scope, often require activated substrates, or do not allow access to desirable functionality, such as alkenyl C­(sp²)–F or chiral C­(sp³)–F centers. Here, we report the formation of new alkenyl and alkyl C–F bonds in the coordination sphere of ruthenium via an unprecedented outer-sphere electrophilic fluorination mechanism. The organometallic species involved are derived from nonactivated substrates (pyridine and terminal alkynes), and C–F bond formation occurs with full regio- and diastereoselectivity. The fluorinated ligands that are formed are retained at the metal, which allows subsequent metal-mediated reactivity

Outer-Sphere Electrophilic Fluorination of Organometallic Complexes

Organofluorine chemistry plays a key role in materials science, pharmaceuticals, agrochemicals, and medical imaging. However, the formation of new carbon–fluorine bonds with controlled regiochemistry and functional group tolerance is synthetically challenging. The use of metal complexes to promote fluorination reactions is of great current interest, but even state-of-the-art approaches are limited in their substrate scope, often require activated substrates, or do not allow access to desirable functionality, such as alkenyl C­(sp²)–F or chiral C­(sp³)–F centers. Here, we report the formation of new alkenyl and alkyl C–F bonds in the coordination sphere of ruthenium via an unprecedented outer-sphere electrophilic fluorination mechanism. The organometallic species involved are derived from nonactivated substrates (pyridine and terminal alkynes), and C–F bond formation occurs with full regio- and diastereoselectivity. The fluorinated ligands that are formed are retained at the metal, which allows subsequent metal-mediated reactivity

Interactions in Water–Ionic Liquid Mixtures: Comparing Protic and Aprotic Systems

The sensitivity of ionic liquids (ILs) to water affects their physical and chemical properties, even at relatively low concentrations, yet the structural thermodynamics of protic IL– (PIL−) water systems at low water concentrations still remains unclear. Using the rigorous Kirkwood–Buff theory of solutions, which can quantify the interactions between species in IL–water systems solely from thermodynamic data, we have shown the following: (1) Between analogous protic and aprotic ILs (AILs), the AIL cholinium bis­(trifluoromethanesulfonyl)­imide ([Ch]­[NTf₂]) shows stronger interactions with water at low water concentrations, with the analogous PIL <i>N</i>,<i>N</i>-dimethylethanolammonium bis­(trifluoromethanesulfonyl)­imide ([DMEtA]­[NTf₂]) having stronger water–ion interactions at higher water contents, despite water–ion interactions weakening with increasing water content in both systems. (2) Water has little effect on the average ion–ion interactions in both protic and aprotic ILs, aside from the AIL [Ch]­[NTf₂], which shows a strengthening of ion–ion interactions with increasing water content. (3) Self-association of water in both PIL–water systems leading to the presence of large aggregates of water in IL-rich compositions has been inferred. Water–water interactions in [DMEtA]­[NTf₂] were found to be similar to those of dialkylimidazolium AILs, whereas these interactions were much larger in the PIL <i>N,N</i>-dimethylethanolammonium propionate ([DMEtA]­[Pr]), attributed to the change in anion–water interactions

Ruthenium-Mediated C–H Functionalization of Pyridine: The Role of Vinylidene and Pyridylidene Ligands

A combined experimental and theoretical study has demonstrated that [Ru­(η⁵-C₅H₅)­(py)₂(PPh₃)]⁺ is a key intermediate, and active catalyst for, the formation of 2-substituted <i>E</i>-styrylpyridines from pyridine and terminal alkynes HCCR (R = Ph, C₆H₄-4-CF₃) in a 100% atom efficient manner under mild conditions. A catalyst deactivation pathway involving formation of the pyridylidene-containing complex [Ru­(η⁵-C₅H₅)­(κ³-<i>C</i>₃-C₅H₄NCHCHR)­(PPh₃)]⁺ and subsequently a 1-ruthanaindolizine complex has been identified. Mechanistic studies using ¹³C- and D-labeling and DFT calculations suggest that a vinylidene-containing intermediate [Ru­(η⁵-C₅H₅)­(py)­(CCHR)­(PPh₃)]⁺ is formed, which can then proceed to the pyridylidene-containing deactivation product or the desired product depending on the reaction conditions. Nucleophilic attack by free pyridine at the α-carbon in this complex subsequently leads to formation of a C–H agostic complex that is the branching point for the productive and unproductive pathways. The formation of the desired products relies on C–H bond cleavage from this agostic complex in the presence of free pyridine to give the pyridyl complex [Ru­(η⁵-C₅H₅)­(C₅H₄N)­(CCHR)­(PPh₃)]. Migration of the pyridyl ligand (or its pyridylidene tautomer) to the α-carbon of the vinylidene, followed by protonation, results in the formation of the 2-styrylpyridine. These studies demonstrate that pyridylidene ligands play an important role in both the productive and nonproductive pathways in this catalyst system

Univalent Gallium Salts of Weakly Coordinating Anions: Effective Initiators/Catalysts for the Synthesis of Highly Reactive Polyisobutylene

The scope of the univalent gallium salts [Ga­(C₆H₅F)₂]⁺[Al­(OR^F)₄]⁻ and the new completely characterized [Ga­(1,3,5-Me₃C₆H₃)₂]⁺[Al­(OR^F)₄]⁻ (R^F = C­(CF₃)₃) was investigated in terms of initiating or catalyzing the synthesis of highly reactive poly­(2-methylpropylene)highly reactive polyisobutylene (HR-PIB)in several solvents. A series of polymerization reactions proved the high efficiency and quality of the univalent gallium salts for the polymerization of isobutylene. The best results were obtained using very low concentrations of [Ga­(C₆H₅F)₂]⁺[Al­(OR^F)₄]⁻ (down to 0.007 mol%) while working at reaction temperatures of up to ±0 °C and in the noncarcinogenic and non-water hazardous solvent toluene. Under these conditions, HR-PIB with an α-content of terminal olefinic double bonds up to 91 mol% and a molecular weight of 1000–2000 was obtained in good yields. Upon changing [Ga­(C₆H₅F)₂]⁺[Al­(OR^F)₄]⁻ for the electron richer [Ga­(1,3,5-Me₃C₆H₃)₂]⁺[Al­(OR^F)₄]⁻, polymerization temperatures could be increased to +10 °C. The reactivity of the gallium­(I) cations therefore seems to be tunable through ligand exchange reactions. Experimental results, density functional theory calculations, and mass spectrometric investigations point toward a coordinative polymerization mechanism

Univalent Gallium Salts of Weakly Coordinating Anions: Effective Initiators/Catalysts for the Synthesis of Highly Reactive Polyisobutylene

The scope of the univalent gallium salts [Ga­(C₆H₅F)₂]⁺[Al­(OR^F)₄]⁻ and the new completely characterized [Ga­(1,3,5-Me₃C₆H₃)₂]⁺[Al­(OR^F)₄]⁻ (R^F = C­(CF₃)₃) was investigated in terms of initiating or catalyzing the synthesis of highly reactive poly­(2-methylpropylene)highly reactive polyisobutylene (HR-PIB)in several solvents. A series of polymerization reactions proved the high efficiency and quality of the univalent gallium salts for the polymerization of isobutylene. The best results were obtained using very low concentrations of [Ga­(C₆H₅F)₂]⁺[Al­(OR^F)₄]⁻ (down to 0.007 mol%) while working at reaction temperatures of up to ±0 °C and in the noncarcinogenic and non-water hazardous solvent toluene. Under these conditions, HR-PIB with an α-content of terminal olefinic double bonds up to 91 mol% and a molecular weight of 1000–2000 was obtained in good yields. Upon changing [Ga­(C₆H₅F)₂]⁺[Al­(OR^F)₄]⁻ for the electron richer [Ga­(1,3,5-Me₃C₆H₃)₂]⁺[Al­(OR^F)₄]⁻, polymerization temperatures could be increased to +10 °C. The reactivity of the gallium­(I) cations therefore seems to be tunable through ligand exchange reactions. Experimental results, density functional theory calculations, and mass spectrometric investigations point toward a coordinative polymerization mechanism

Reactive-Atom Scattering from Liquid Crystals at the Liquid–Vacuum Interface: [C₁₂mim][BF₄] and 4‑Cyano-4′-Octylbiphenyl (8CB)

Two complementary approaches were used to study the liquid–vacuum interface of the liquid-crystalline ionic liquid 1-dodecyl-3-methyl­imidazolium tetrafluoroborate ([C₁₂mim]­[BF₄]) in the smectic A (SmA) and isotropic phases. O atoms with two distinct incident translational energies were scattered from the surface of [C₁₂mim]­[BF₄]. Angle-dependent time-of-flight distributions and OH yields, respectively, were recorded from high- and low-energy O atoms. There were no significant changes in the measurements using either approach, nor the properties derived from them, accompanying the transition from the SmA to the isotropic phase. This indicates that the surface structure of [C₁₂mim]­[BF₄] remains essentially unchanged across the phase boundary, implying that the bulk order and surface structure are not strongly correlated for this material. This effect is ascribed to the strong propensity for the outer surfaces of ionic liquids to be dominated by alkyl chains, over an underlying layer rich in anions and cation head groups, whether or not the bulk material is a liquid crystal. In a comparative study, the OH yield from the surface of the liquid crystal, 8CB, was found to be affected by the bulk order, showing a surprising step increase at the SmA–nematic transition temperature, whose origin is the subject of speculation