Improving selectivity in catalytic hydrodefluorination by limiting S_NV reactivity

Abstract

Catalytic hydrodefluorination of perfluoroallylbenzene with CpTiH in THF is unselective and yields a variety of previously unknown compounds, predominantly activated in the allylic position. Several different mechanisms have been examined in detail using solvent corrected (THF) DFT(M06-2X) calculations for the archetypal perfluorinated olefin perfluoropropene and perfluoroallylbenzene: (a) single electron transfer, (b) hydrometallation/fluoride elimination, (c) σ-bond metathesis (allylic or vinylic), and (d) nucleophilic vinylic substitution (SV, w/o Ti-F contacts in the TS). SV is shown to be a competitive mechanism to hydrometallation and proceeds via ionic species from which F-elimination is facile and unselective leading to low selectivity in polar solvents. Subsequent experiments show that selectivity can be increased in a non-polar solvent.

Catalyst Mileage in Olefin Polymerization: The Peculiar Role of Toluene

“…Final single-point energies were calculated at the M06-2X level of theory employing triple-ζ Dunning (TZ) basis sets (cc-pVTZ quality) . In addition to main-group-metal chemistry, ,− we found that this protocol accurately reproduces different experimental problems concerning d 0 and d 1 early-transition-metal systems in olefin polymerization (including Ti–C homolysis) ,,,− and Ti­(III) chemistry. − An additional cross-check on system 1′-Ph showed that results using the ωB97xd functional produced similar results. In the case of the 1′-Ph ion pair with B­(C 6 F 5 ) 4 – , only a single structure was optimized for the doublet species and the INS TS, and the given ΔΔ G ⧧ HOM‑INS value (see the Supporting Information) can likely be regarded only as an upper limit.…”

Organocatalytic C−F Bond Activation with Alanes

“…Finally, we have demonstrated that the choice of solvent can influence the selectivity in HDF reactions . Nonpolar solvents disfavor charge delocalization, which increases S N V barrier heights, thereby increasing selectivity.…”

“…HDF via the aluminum hydride monomer 1M proceeds preferentially via a hydrometallation–elimination sequence associated with high barriers (40–48 kcal mol −1 , when the dimerization equilibrium is factored in and predominantly enthalpic). Hydrometallation is rate limiting but elimination is selectivity determining and would yield the thermodynamically most stable Z ‐isomer 3 a in high selectivity; as all elimination TS's are energetically early but geometrically late their relative energy differences reflect those found in the products, very similar to HDF using Cp 2 TiH …”

Chlorodefluorination of Fluoromethanes and Fluoroolefins at a Lewis Acidic Aluminum Fluoride

“…However, as olefin coordination is not favored (see below), such a pathway is less likely. On the other hand, chloride attack at an olefin after silane coordination at the surface would also result in an S N V type mechanism, [34] but at least tertiary silanes show typically silylium ion type reactivity [7e,f,22b] …”