Carbon-Fluorine Bond Activation of Tetrafluoroethylene on Palladium(0) and Nickel(0): Heat or Lewis Acidic Additive Promoted Oxidative Addition

The C-F bond cleavage reaction of tetrafluoroethylene (TFE; CF2=CF2) with an M(0) complex (M = Pd, Ni) was investigated. The treatment of an M(0) precursor with TFE in the presence of the appropriate monodentate phosphine ligand led to a clean formation of the corresponding, eta(2)-TFE adduct (eta(2)-TFE)M(PR3)(2). In the case of the Ni(0) species, in particular, the choice of phosphine ligands is crucial for the preparation of the desired eta(2)-TFE complex: the use of either PCy3 or (PPr3)-Pr-i resulted in the target adduct, while less sterically hindered phosphines such as PPh3 and (PBu3)-Bu-n gave the known octafluoronickelacyclopentane as a result of the oxidative cyclization of two TFE molecules. Thermolysis of both palladium and nickel eta(2)-TFE adducts bearing PCy3 as the ligand resulted in a C-F bond activation reaction and gave the corresponding (trifluorovinyl)metal fluorides, trans-(PCy3)(2)M(F)(CF=CF2): The reaction of (eta(2)-TFE)Pd(PPh3)(2) with Lil as an additive allowe d cleavage of the C F bond in THF, even at room temperature, and gave trans-(PPh3)(2)Pd(I)(CF=CF2) with a concomitant formation f lithium fluoride. Other metal halides, such as MgBr2 and AlCl3, also promoted the C F bond cleavage of TFE.In addition, the use of either BF3 center dot Et2O or B(C6F5)(3) exerted a similar accelerative effect on the,C-F bond activation of TFE on either nickel or palladium. The molecular structures of a series of eta(2)-TFE and trifluorovinyl complexes were unambiguously determined by Means of X-ray crystallography. The resultant (trifluorovinyl)palladium or -nickel species have shown the potential to utilize a key intermediate in cross-coupling reactions with organometallic reagents to prepare a variety of trifluorovinyl compounds.