Selective Copper Complex-Catalyzed Hydrodefluorination of Fluoroalkenes and Allyl Fluorides: A Tale of Two Mechanisms

Abstract

The transition to more economically friendly small-chain fluorinated groups is leading to a resurgence in the synthesis and reactivity of fluoroalkenes. One versatile method to obtain a variety of commercially relevant hydrofluoroalkenes involves the catalytic hydrodefluorination (HDF) of fluoroalkenes using silanes. In this work it is shown that copper hydride complexes of tertiary phosphorus ligands (L) can be tuned to achieve selective multiple HDF of fluoroalkenes. In one example, HDF of the hexafluoropropene dimer affords a single isomer of heptafluoro-2-methylpentene in which five fluorines have been selectively replaced with hydrogens. DFT computational studies suggest a distinct HDF mechanisms for L2CuH (bidentate or bulky monodentate phosphines) and L3CuH (small cone angle monodentate phosphines) catalysts, allowing for stereocontrol of the HDF of trifluoroethylene.

Application of Industrially Relevant HydroFluoroOlefin (HFO) Gases in Organic Syntheses

“…25c In a detailed experimental and theoretical mechanistic study, Baker, Ehm, and co-workers demonstrated that triphenylphosphine-copper hydride is an excellent catalyst for the hydrodefluorination of various fluoroalkenes using silanes. 29…”

“…In 2018, Skalenko and his co-workers developed a method for the synthesis of 3-azabicyclo[3.2.0]heptanes (29) from N-benzylmaleimide (28) and alkenes by [2+2] photocycloaddition (Scheme 3D). 17 The reactions take place in the presence of benzophenone as photosensitizer, mostly with moderate yields.…”

“…28 In a detailed experimental and theoretical mechanistic study Baker, Ehm and coworkers demonstrated that triphenylphosphino-copper hydride is an excellent catalyst for the hydrodefluorination of various fluoroalkenes using silanes. 29 Hydrodefluorination was extended to perfluoroarenes by Lentz and co-workers, and it was shown experimentally and by calculations that Cp2TiH facilitates C-F bond cleavage and replaces the F atom with hydrogen through a Meisenheimer type complex intermediate. 30 The presence of fluorides in the olefin moiety facilitates the nucleophilic vinylic substitution process through additionelimination steps.…”

Competing C–H and C–F bond activation reactions of a fluorinated olefin at Rh: a fluorido vinylidene complex as an intermediate in an unprecedented dehydrofluorination step

“…[6][7][8][9][10][11][12] Commonly, the C-F bond activation is promoted by the formation of stable bonds such as H-F, B-F, Si-F or Al-F bonds among others. [13][14][15][16][17][18] At rhodium, the complexes [Rh(E)(PEt 3 ) 3 ] (E ¼ H, F, boryl, silyl, germyl) exhibit distinct reaction pathways for the C-F or C-H bond activation of HFOs. [19][20][21][22][23][24][25] For example, the activation of 2,3,3,3-tetrauoropropene using [Rh(F)(PEt 3 ) 3 ] in the presence of uorosilane resulted in the C-H bond activation and a concomitant 1,2-uorine shi.…”

Synthesis of Polycyclic Furan and Chromene Derivatives via Cascade Reactions Enabled by Cleavage of Multiple C(sp3)−F Bonds

“…bond formation and precise retention of partially fluorinated scaffold, although most of the advances focus on the manipulation of single CÀ F bond. Compared with more activated aromatic [21][22][23][24][25] or vinylic analogues, [26][27][28][29][30][31][32][33] selective aliphatic C(sp 3 )À F functionalization of unreactive perfluoroalkyl substance with multiple CÀ F bonds attached remote to π-system is relatively uncommon. [34][35][36][37][38][39][40][41][42][43][44][45][46][47] The successful realization of this challenging issue is complicated by several apparent factors (Scheme 1A).…”