Nickel-catalyzed alkyl-arylation of 3,3,3-trifluoropropene

Owing to the versatile synthetic utility of its carbon-carbon double bond, low-cost industrial chemical 3,3,3-trifluoropropene (TFP) represents one of the most straightforward and cost-efficient precursors to prepare trifluoromethylated compounds. However, only limited methods for the efficient transformations of TFP have been reported so far. Here, we report a nickel-catalyzed dicarbofunctionalization of TFP. The reaction uses inexpensive NiCl2·6H2O as the catalyst and 4,4'-biMeO-bpy and PCy2Ph as the ligands, allowing the alkyl-arylation of TFP with a variety of tertiary alkyl iodides and arylzinc reagents in high efficiency. This nickel-catalyzed process overcomes the previous challenges by suppressing β-H and β-F eliminations from TFP, rendering this strategy effective for the transformations of TFP into medicinal interest trifluoromethylated compounds.

Rhodium(I) Complexes as Useful Tools for the Activation of Fluoroolefins

In this account we describe studies on the reactivity of rhodium(I) complexes of the type [Rh(E)(PEt3)3], where E represents hydrido, fluorido, germyl, boryl or silyl ligands, towards fluorinated olefins. The results are compared with those reported by other research groups on fluoroolefins, as well as with the chemistry of compounds [Rh(E)(PEt3)3] towards fluoroaromatics in terms of selectivity and mechanisms.

1 Introduction

2 Reactivity Towards Fluoroolefins

2.1 Reactivity of Hexafluoropropene

2.2 Reactivity of (E)-1,2,3,3,3-Pentafluoropropene

2.3 Reactivity of 2,3,3,3-Tetrafluoropropene and (E)-1,3,3,3-Tetrafluoropropene

2.4 Reactivity of 3,3,3-Trifluoropropene

2.5 Reactivity of Pentafluorostyrene

3 Conclusion and Perspective

Modern applications of low-valent early transition metals in synthesis and catalysis

Low-valent early transition metals are often intrinsically highly reactive as a result of their strong propensity toward oxidation to more stable high-valent states. Harnessing these highly reducing complexes for productive reactivity is potentially powerful for C-C bond construction, organic reductions, small-molecule activation and many other reactions that offer orthogonal chemoselectivity and/or regioselectivity patterns to processes promoted by late transition metals. Recent years have seen many exciting new applications of low-valent metals through building new catalytic and/or multicomponent reaction manifolds out of classical reactivity patterns. In this Review, we survey new methods that employ early transition metals and invoke low-valent precursors or intermediates in order to identify common themes and strategies in synthesis and catalysis.

Group 4 Metallocene Difluoride/Palladium Bimetallic Catalysts for the Reductive Cross-Coupling of Alkynes with Aryl Iodides and Bromides

A novel protocol has been developed for the selective synthesis of ( E)-alkenes via the reductive cross-coupling of alkynes and aryl halides using a bimetallic catalyst system composed of a group 4 metallocene difluoride (Cp₂[M]F₂; [M] = Hf or Zr; Cp = cyclopentadienide) and palladium dichloride. This reaction proceeds via a coupling between an aryl halide and an in situ generated alkenyl metallocene intermediate derived from the group 4 metallocene difluoride, a hydrosilane, and an alkyne. For a catalytic reductive coupling, the addition of sodium fluoride (NaF) to the reaction system is required. Moreover, in the presence of NaF, a ligand exchange was observed by NMR spectroscopy in hafnocene diiodide (Cp₂HfI₂) to afford hafnocene difluoride (Cp₂HfF₂).

Palladium-Catalyzed Reductive Coupling Reaction of Terminal Alkynes with Aryl Iodides Utilizing Hafnocene Difluoride as a Hafnium Hydride Precursor Leading to trans-Alkenes

Herein, we describe a reductive cross-coupling of alkynes and aryl iodides by using a novel catalytic system composed of a catalytic amount of palladium dichloride and a promoter precursor, hafnocene difluoride (Cp₂ HfF₂ , Cp=cyclopentadienyl anion), in the presence of a mild reducing reagent, a hydrosilane, leading to a one-pot preparation of trans-alkenes. In this process, a series of coupling reactions efficiently proceeds through the following three steps: (i) an initial formation of hafnocene hydride from hafnocene difluoride and the hydrosilane, (ii) a subsequent hydrohafnation toward alkynes, and (iii) a final transmetalation of the alkenyl hafnium species to a palladium complex. This reductive coupling could be chemoselectively applied to the preparation of trans-alkenes with various functional groups, such as an alkyl group, a halogen, an ester, a nitro group, a heterocycle, a boronic ester, and an internal alkyne.

Synthesis of a rhodium(i) germyl complex: a useful tool for C–H and C–F bond activation reactions

The rhodium(i) germyl complex [Rh(GePh₃)(PEt₃)₃] is a useful tool for C–F and C–H bond activation reactions. For instance, treatment with hexafluoropropene results in the formation of two isomeric C–F activation products [Rh{(E)-CFCF(CF₃)}(PEt₃)₃] and [Rh{(Z)-CFCF(CF₃)}(PEt₃)₃] in a 3 : 1 ratio.

Competing reaction pathways of 3,3,3-trifluoropropene at rhodium hydrido, silyl and germyl complexes: C–F bond activation versus hydrogermylation

The reactivity of the Rh complexes [Rh(L)(PEt₃)₃] (L = H, Si(OEt)₃, GePh₃) towards CH₂CHCF₃ was investigated which involve C–F bond activation and germylation reactions.

Improving selectivity in catalytic hydrodefluorination by limiting SNV reactivity

Competition of HM, SBM and S_NV in hydrodefluorination can lead to low selectivity which can be improved via solvent change.

Synthesis of monofluoroalkenes through selective hydrodefluorination of gem-difluoroalkenes with Red-Al®

A practical approach for the selective hydrodefluorination of gem-difluoroalkenes using Red-Al® as reductant at room temperature in CH₂Cl₂ was reported. Monofluoroalkenes were obtained in moderate to high yields with good E-selectivity.

C-F activation at rhodium boryl complexes: formation of 2-fluoroalkyl-1,3,2-dioxaborolanes by catalytic functionalization of hexafluoropropene

Fluorinated building blocks by C-F bond cleavage: Catalytic C-F activation reactions that give novel dioxaborolanes have been developed (see scheme). The reactions proceed at room temperature, and catalytic intermediates are presumably rhodium hydride and boryl species.