Selective Hydrodefluorination of Hexafluoropropene to Industrially Relevant Hydrofluoroolefins

Abstract

The selective hydrodefluorination of hexafluoropropene to HFO-1234ze and HFO-1234yf can be achieved by reaction with simple group 13 hydrides of the form EH 3 •L (E = B, Al; L = SMe 2 , NMe 3). The chemoselectivity varies depending on the nature of the group 13 element. A combination of experiments and DFT calculations show that competitive nucleophilic vinylic substitution and addition-elimination mechanisms involving hydroborated intermediates lead to complementary selectivities.

Defluoroalkylation of sp3 C−F Bonds of Industrially Relevant Hydrofluoroolefins

“…Abstract: As imple, one-pot procedure is reported for the selective defluoroalkylation of trifluoromethyl alkene derivatives with aldehydes and ketones. The reaction sequencea llows construction of an ew CÀCb ond in a highly selectivem anner from as ingle sp 3 CÀFb ond of a CF 3 group in the presence of sp 2 CÀFbonds. The scope incorporates industrially relevant fluorocarbons including HFO-1234yf and HFO-1234ze.…”

“…The majority of modernr efrigerants also contain at least one trifluoromethyl group. This includes 2,3,3,3-tetrafluoropropene (HFO-1234yf), [3] which is being positioned as ad irect replacement for 1,2,2,2tetrafluoroethane( HFC-134a) the most abundantr efrigerant in the automotive sector.T he ubiquity of the trifluoromethyl group stems in part from its chemical robustness.T he sp 3 CÀF bonds are strong and reluctant to furtherc hemical transformations. When reactions do occur,t hey are often complicated by low chemoselectivity as CÀFb ond strengths become weaker across the series CF 3 > CF 2 H > CFH 2 .…”

“…When reactions do occur,t hey are often complicated by low chemoselectivity as CÀFb ond strengths become weaker across the series CF 3 > CF 2 H > CFH 2 . [4] Only recently have synthetic methods emerged for the selective alkylation or arylation of as ingle sp 3 CÀFb ond of the trifluoromethyl group. [5,6] These transformations are highly desirable, not only because they reveal the trifluoromethyl moiety as ap oint for functional group interconversions, but also because they generate ad ifluoromethyleneu nit through am odular carbon-carbonb ond forming step.…”

“…An umber of functional groups survive the carbon-carbon bond forming step, includingr emote alkenes,aryl methyle thers and aryl bro- Chemistry-A European Journal mides.W hile an a,b-unsaturated carbonyl reacts by selective 1,2-addition, under the conditions examined there was no evidence for carbon-carbon bond formation for imines, esters or amides. The method is selective for sp 3 CÀFo ver sp 2 CÀF bonds and does not proceed past synthetic modification of a single CÀFb ond of the CF 3 group.…”

“…We have proposed ar elatedm echanism in the hydrodefluorination of hexafluoropropene by borane reagents. [3] Hence it is likely that, 3a derives from as electives p 3 C-F defluoroalkylation and sp 2 C-F hydrodefluorination sequence.…”