Exposing the Origins of Irreproducibility in Fluorine NMR Spectroscopy.

Fluorine chemistry has taken a pivotal role in chemical reaction discovery, drug development, and chemical biology. NMR spectroscopy, arguably the most important technique for the characterization of fluorinated compounds, is rife with highly inconsistent referencing of fluorine NMR chemical shifts, producing deviations larger than 1 ppm. Herein, we provide unprecedented evidence that both spectrometer design and the current unified scale system underpinning the calibration of heteronuclear NMR spectra have unintentionally led to widespread variation in the standardization of 19 F NMR spectral data. We demonstrate that internal referencing provides the most robust, practical, and reproducible method whereby chemical shifts can be consistently measured and confirmed between institutions to less than 30 ppb deviation. Finally, we provide a comprehensive table of appropriately calibrated chemical shifts of reference compounds that will serve to calibrate 19 F spectra correctly.

Copper(I) and silver(I) bis(trifluoromethanesulfonyl)imide and their interaction with an arene, diverse olefins, and an NTf2(-)-based ionic liquid.

The chemistry of coinage metal bis(triflyl)imides of technological interest, CuNTf(2) and AgNTf(2), their synthesis and complexes with excess of comparatively weakly coordinating NTf(2)(-) as well as with ether, olefins, and the arene mesitylene are described. The existence of the solvent-free pure phase [CuNTf(2)](∞) has not been evidenced so far. Contrary to the literature, in which the preparation of [CuNTf(2)](∞) is supposed to be carried out by reacting mesityl copper, [Cu(Mes)](5), and HNTf(2), we found that in fact this reaction leads reproducibly to the interesting copper diarene sandwich complex [Cu(η(3)-MesH)(2)][Cu(NTf(2))(2)] (1) (MesH = 1,3,5-trimethylbenzene). The unexpectedly stable molecular etherate [Cu(Et(2)O)(NTf(2))] (2) turned out to be the best precursor for CuNTf(2) having only an inert and easily exchangeable solvent ligand. The coordination mode of NTf(2)(-) in 1 and 2 as well as in the hitherto unknown crystalline phase of [AgNTf(2)](∞) (3) is described. The complex formation, which takes place when dissolving 2 or 3 in the room temperature ionic liquid (RTIL) [emim]NTf(2) ([emim](+) = 1-ethyl-3-methylimidazolium), has been studied. Furthermore, the reaction of 1-3 towards the diolefins 1,5-cyclooctadiene (COD), 2,5-norbornadiene (NBD) and isoprene (2-methylbuta-1,3-diene) and towards ethylene has been investigated. The products 4-13 of these conversions have been isolated and fully characterized by NMR- and IR spectroscopies, mass spectrometry, and elemental- and XRD analyses. The potential of [Cu(η(3)-MesH)(2)][Cu(NTf(2))(2)] (1), [Cu(Et(2)O)(NTf(2))] (2) and [AgNTf(2)](∞) (3) as well as of [emim][M(NTf(2))(2)] (M = Cu 4, Ag 5) as chemisorbers for ethylene was studied by NMR spectroscopy.