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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(sp(2))-F or chiral C(sp(3))-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.

A combined experimental and theoretical study has demonstrated that [Ru(η(5)-C(5)H(5))(py)(2)(PPh(3))](+) is a key intermediate, and active catalyst for, the formation of 2-substituted E-styrylpyridines from pyridine and terminal alkynes HC≡CR (R = Ph, C(6)H(4)-4-CF(3)) in a 100% atom efficient manner under mild conditions. A catalyst deactivation pathway involving formation of the pyridylidene-containing complex [Ru(η(5)-C(5)H(5))(κ(3)-C(3)-C(5)H(4)NCH═CHR)(PPh(3))](+) and subsequently a 1-ruthanaindolizine complex has been identified. Mechanistic studies using (13)C- and D-labeling and DFT calculations suggest that a vinylidene-containing intermediate [Ru(η(5)-C(5)H(5))(py)(═C═CHR)(PPh(3))](+) 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(η(5)-C(5)H(5))(C(5)H(4)N)(═C═CHR)(PPh(3))]. 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.

We have developed a simple and quantitative explanation for the relatively low melting temperatures of ionic liquids (ILs). The basic concept was to assess the Gibbs free energy of fusion (Delta(fus)G) for the process IL(s) --IL(l), which relates to the melting point of the IL. This was done using a suitable Born-Fajans-Haber cycle that was closed by the lattice (i.e., IL(s) --IL(g)) Gibbs energy and the solvation (i.e., IL(g) --IL(l)) Gibbs energies of the constituent ions in the molten salt. As part of this project we synthesized and determined accurate melting points (by DSC) and dielectric constants (by dielectric spectroscopy) for 14 ionic liquids based on four common anions and nine common cations. Lattice free energies (Delta(latt)G) were estimated using a combination of Volume Based Thermodynamics (VBT) and quantum chemical calculations. Free energies of solvation (Delta(solv)G) of each ion in the bulk molten salt were calculated using the COSMO solvation model and the experimental dielectric constants. Under standard ambient conditions (298.15 K and 10(5) Pa) Delta(fus)G degrees was found to be negative for all the ILs studied, as expected for liquid samples. Thus, these ILs are liquid under standard ambient conditions because the liquid state is thermodynamically favorable, due to the large size and conformational flexibility of the ions involved, which leads to small lattice enthalpies and large entropy changes that favor melting. This model can be used to predict the melting temperatures and dielectric constants of ILs with good accuracy. A comparison of the predicted vs experimental melting points for nine of the ILs (excluding those where no melting transition was observed and two outliers that were not well described by the model) gave a standard error of the estimate (s(est)) of 8 degrees C. A similar comparison for dielectric constant predictions gave s(est) as 2.5 units. Thus, from very little experimental and computational data it is possible to predict fundamental properties such as melting points and dielectric constants of ionic liquids.