2366-32-7Relevant articles and documents
Organocatalytic C?F Bond Activation with Alanes
Jaeger, Alma D.,Ehm, Christian,Lentz, Dieter
supporting information, p. 6769 - 6777 (2018/04/02)
Hydrodefluorination reactions (HDF) of per- and polyfluorinated olefins and arenes by cheap aluminum alkyl hydrides in non-coordinating solvents can be catalyzed by O and N donors. TONs with respect to the organocatalysts of up to 87 have been observed. Depending on substrate and concentration, high selectivities can be achieved. For the prototypical hexafluoropropene, however, low selectivities are observed (E/Z≈2). DFT studies show that the preferred HDF mechanism for this substrate in the presence of donor solvents proceeds from the dimer Me4Al2(μ-H)2?THF by nucleophilic vinylic substitution (SNV)-like transition states with low selectivity and without formation of an intermediate, not via hydrometallation or σ-bond metathesis. In the absence of donor solvents, hydrometallation is preferred but this is associated with inaccessibly high activation barriers at low temperatures. Donor solvents activate the aluminum hydride bond, lower the barrier for HDF significantly, and switch the product preference from Z to E. The exact nature of the donor has only a minimal influence on the selectivity at low concentrations, as the donor is located far away from the active center in the transition states. The mechanism changes at higher donor concentrations and proceeds from Me2AlH?THF via SNV and formation of a stable intermediate, from which elimination is unselective, which results in a loss of selectivity.
Experimental and theoretical studies of the vibrational spectra of cis-1-bromo-2-fluoroethene
Baldacci,Stoppa,Charmet, A. Pietropolli,Scaranto,Gambi
, p. 1967 - 1975 (2007/10/03)
The gas-phase infrared spectrum of cis-1-bromo-2-fluoroethene has been studied at low resolution in the range 200-6500cm-1, leading to a complete assignment of the fundamentals, except the lowest vibrational mode ν9 predicted at 167cm-1. The remaining vibrational structure has been mainly interpreted in terms of first overtone or two quanta combination bands. Isotopic 79/81Br shift has been observed only in the ν8 fundamental. The equilibrium structure and the quadratic force field have been investigated theoretically at CCSD(T) level of theory employing Dunning's correlation consistent triple-zeta basis set. Cubic and semidiagonal quartic force field have been calculated using second-order M?ller-Plesset perturbation theory and Ahlrich' split valence (SV) contracted basis set. After a minor scaled quantum mechanical (SQM) adjustment of the quadratic force constants, the vibrational analysis, based on the second-order perturbation theory, has been carried out with the calculated force constants.
Vibrational Excitation of the Reaction between Vinyl Bromide and Fluorine in Solid Argon
Cesaro, Stella Nunziante,Frei, Heinz,Pimentel, George C.
, p. 2142 - 2147 (2007/10/02)
A number of unsuccessful attempts to induce bimolecular addition reactions with selective vibrational excitation in cryogenic solids are reported here: 1,3-butadiene with Cl2, ClF, Br2, I2, and XeF2; vinyl chloride with F2.One system, vinyl bromide with fluorine in solid argon, did respond by showing reaction product growth upon laser excitation at 3116, 3098, 1849, 1808, and 1605 cm-1.Identification of reaction products suggests F2 addition across the double bond followed significantly by HF elimination but apparently without HBr elimination.Relative quantum yields display a monotonic dependence upon photon energy that is even more dramatic than that found earlier for the ethylene-fluorine reaction.Thus excitation of the C-H stretching modes either at 3116 or 3098 cm-1 is 102 times more effective than excitation at 1849 or 1848 cm-1 and 103 times more effective than at 1605 cm-1.
