Palladium complexes fluoride

Besides rhodium catalysts, palladium complex also can catalyze the addition of aryltrialkoxysilanes to a,(3-unsaturated carbonyl compounds (ketones, aldehydes) and nitroalkenes (Scheme 60).146 The addition of equimolar amounts of SbCl3 and tetrabutylammonium fluoride (TBAF) was necessary for this reaction to proceed smoothly. The arylpalladium complex, generated by the transmetallation from a putative hypercoordinate silicon compound, was considered to be the catalytically active species. 

When KI is added to a solution of palladium(II) chloride, an insoluble diiodide is precipitated. The dark red-black crystals are soluble in excess iodide with form a (ion of rhe tetraiodide complex ion. Palladinm(TT) iodide evolves iodine at 100°C, the decomposition to the elements being complete at 330-360°C, The black compound, palladium(III) fluoride, is made by direct combination of the elements. On rednetion. the brown difluoiide is formed,... 

Equation 76) <1993OM3019>, which react as ester and ketone enolate equivalents, respectively. The latter reaction requires the use of fluoride ion activation (tetrabutylammonium fluoride, TBAF) to actuate the addition. Central carbon alkylation is less common for allylpalladium reactions despite this, nucleophilic alkylation of TMEDA-stabilized 1,3-diphenylallyl palladium complexes proceeds selectively to the central carbon (Equation 77) <1995AGE100>. 

N. Bartlett and J. W. Quail, The Preparation of Palladium Difluoride and Complex Fluorides of Palladium in Selenium Tetrafluoride, J. Chem. Soc. (1961) 3728-3732. 

Palladium-catalyzed cross couplings of organofluorosilanes with vinyl [37] and aryl [38] halides and triflates are known, where the activation of the Si—C bond by fluoride ion plays an essential role in the coupling. The pentacoordinated fluoroorganic silanes promote the transmetallation to the aryl halide-palladium complexes strongly. At least one fluorine... 

Preparation. - Fluorophosphines have been obtained from the reactions of the related chlorophosphines with trimethyl tin fluoride. Phenyl(isopropyl)-fluorophosphine has been resolved via a chiral amine-palladium(II) complex, providing the first example of the resolution of a free fluorophosphine chiral at phosphorus. This compound racemises at 20 °C in benzene solution over six hours. The neat compound rapidly decomposes by redox disproportionation. The same approach has been used for the resolution of the related chloro-phosphine, but the optically active compound could not be liberated unchanged from the crystallised diastereoisomeric palladium complex. The dihalo-genophosphines... 

Ball ND, Sanford MS (2009) Synthesis and reactivity of a mono-a-aryl palladium(IV) fluoride complex. J Am Chem Soc 131 3796-3797... 

For the palladium-catalyzed cyclotrimerization of arynes, a mechanism similar to the accepted mechanism for [2+2+2] cycloaddition of alkynes may be proposed (Scheme 15). Though it has not been studied in depth, some experimental results support it. Firstly, aryne-forming conditions are necessary for the reaction to proceed (see Table 1, entry 8) no reaction of trifiate 55 takes place at room temperature in the presence of the catalyst if fluoride is absent, which rules out a mechanism initiated by the oxidative addition of the aryl trifiate to palladium. Data obtained in the closely related cocycloadditions of benzyne with alkynes, discussed below, hkewise point to benzyne as the reactive species. Secondly, the benzyne-palladium complex 67 is a plausible initial intermediate because the ability of group 10 metals to coordinate benzyne is well known (see Sect. 1.2.2), and although benzyne complexes of palladium have eluded isolation (apparently because of their instability) [7,26], they may well be able to exist as transient intermediates in a catalytic cycle such as that shown in Scheme 15. Thirdly, it is known that benzyne complex 34 can form metallacy-cles similar to 68, albeit with dcpe as hgand instead of PPhj [26]. 

Methods M and N are based on different phosphine ligands which activate the resulting palladium-complex providing higher electron-density at palladium-metallic centre, more reactive catalyst, and very mild reaction conditions [32,35], The excellent-yielding SM reactions of aryl iodides, bromides, as well as chlorides catalysed with Pd2(dba)3 / Pt-Bus (1 2), in the presence of potassium fluoride as the base, smoothly proceed at room temperature [35], Scheme 24. All three isomeric 4-halo-acetophenones, 73, 284, 285, in reaction with 2-tolylboronic acid (286) gave appropriate biaryl 287 in almost quantitative yields. 

In 2001, Nolan reported that NHC-palladium complexes, in combination with a fluoride additive, catalyze the Stille crosselectron-deficient aryl chlorides (Equation 2.44) [80]. 

A palladium complex with an iodine ligand undergoes an exchange in the presence of silver fluoride.234... 

The dimerization of ethylene into n-butenes by means of tetrachlo-robis(ethylene)palladium in nonhydroxylic media (benzene or dioxane) has been attempted [246]. Other palladium salts (fluoride, bromide, iodide, nitrate) tested in the dimerization of olefins do not form complexes of the type (C2H4),Pd2X4. Palladium cyanide dimerizes ethylene twice as slowly as PdCL, probably on account of deactivation of the catalyst by a polyethylene deposit formed along with the dimer. 

The most commonly accepted mechanism for this coupling was initially proposed by Hiyama and Hatanaka, which involves three steps.The first step is the oxidative addition of the aryl halide to the palladium(O) catalyst to give arylpalladium complex 1. The second step involves the transmetallation of the arylpalladium complex 1 with the anionic arylsilicate 2 to give bis(aryl)palladium complex 3. Finally, the cross-coupled product 4 is produced and the palladium(O) catalyst is regenerated through reductive elimination of the bis(aryl)palladium(II) complex 3. The key intermediate to this process is the requirement for the pentacoordinate arylsilicate anion 2, typically formed by treatment of the tetracoordinate silane with the activating anion, such as tetrabutylammonium fluoride (TBAF). 

The intermediate palladium acetate dimers are also suitable precursors for palladium(lV) fluoride complexes (Experimental Procedure below)P ... 

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