210767-70-7Relevant academic research and scientific papers
Bond angle effects on the migratory insertion of ethylene and carbon monoxide into palladium(II)-methyl bonds in complexes bearing bidentate phosphine ligands
Ledford, John,Shultz, C. Scott,Gates, Derek P.,White, Peter S.,DeSimone, Joseph M.,Brookhart, Maurice
, p. 5266 - 5276 (2008/10/08)
Labile (P-P)Pd(CH3)(OEt2)+BAr′4- complexes (2) have been prepared via protonation of (P-P)PdMe2 (1), where P-P = cis-1,2-bis(diphenylphosphino)ethylene (a, dppee), 1,2-bis(diphenylphosphino)benzene (b, dpbz), 1,2-bis(diphenylphosphino)ethane (c, dppe), 1,2-bis(dimethylphosphino)ethane (d, dmpe), 1,3-bis(diphenylphosphino)propane (e, dppp), 1,3-bis(diisopropylphosphino)propane (f, dippp), 1,4-bis(diphenylphosphino)butane (g, dppb) and Ar′ = 3,5-(CF3)2C6H3. Unstable complex 2d (P-P = dmpe) was generated in situ. X-ray structures are reported for 1e and 2e-g. Treatment of 2a-g with CO in CH2Cl2 at -90 °C yields the (P-P)Pd(CH3)(CO)+ complexes 3a-g. Barriers to migratory insertion in 3a-g were determined with the ordering to be: 3f (dippp) ≈ 3g (dppb) 3)(C2H4)+ (5a-g). Barriers to migratory insertion in these complexes were determined by NMR spectroscopy to be: 5b (dpbz) ≈ 5e (dppp) ≈ 5f (dippp) ≈ 5g (dppb) 2CH3)(C2H4)+ (6a-e,g) produced from 5a-e,g under C2H4 are catalyst resting states for the dimerization of C2H4 to butenes. In the case of 5f (P-P = dippp), the catalyst resting state produced is the β-agostic ethyl complex (dippp)Pd(CH2CH2-μ-H)+ (8f), which has been isolated. This complex exhibits two dynamic processes studied by VT-NMR: interchange of Cα and Cβ (ΔG?=10.3(2) kcal/mol) and rotation of the agostic methyl group (ΔG? ca. 6.4 kcal/mol). The β-agostic propyl complex 7f has been generated and identified as the n-propyl isomer (dippp)-Pd(CH2CH2-μ-HCH3)+.
Reactivity of electrophilic palladium alkyl cations stabilized by electron-rich chelating diphosphine ligands. Evidence for dinuclear intermediates and the formation of a dinuclear mixed-valence methyl cation
Fryzuk, Michael D.,Clentsmith, Guy K. B.,Rettig, Steven J.
, p. 2007 - 2016 (2007/10/03)
The reactivity of the electron-rich palladium alkyl cation, [Pd(dippe)R]+BAr4- (dippe = 1,2-bis(diisopropylphosphino)ethane; R = η3-CH2Ph or CH3; BAr4 = {B[3,5-(F3C)2C6H3]4}) with a variety of small molecules is reported. Although the benzyl cation is unreactive towards carbon monoxide and dihydrogen, the corresponding methyl cation, [Pd(dippe)Me(s)]+ (s = Et2O, THF or o-dichlorobenzene) reacts rapidly with H2 to produce the dihydride-bridged dimer {[(dippe)Pd]2(μ-H)2}2+, and with CO to produce the dinuclear mixed-valence, cationic complex [Pd(dippe)(μ-CO)Pd(dippe)Me][BAr4]. In addition, the methyl cation can abstract alkyl groups from neutral dialkyl complexes; thus, the addition of [Pd(dippe)Me(s)]+ to Pd(dippe)(CH2Ph)2 results in the formation of the methyl benzyl derivative Pd(dippe)Me(CH2Ph) and the cationic benzyl cation [Pd(dippe)(η3-CH2Ph)]+. Methyl group interchange is also observed for the reaction of the methyl cation with the neutral dimethyl; when [Pd(dippe)Me(s)]+ is mixed with Pd(dippe)(13CH3)2, the carbon-13 label is immediately scrambled to the cation. These exchange reactions are suggested to occur via dinuclear intermediates. The mixed-valence dinuclear species mentioned above has been investigated in some detail; mechanistic studies have indicated that the addition of CO to [Pd(dippe)Me(s)]+ probably proceeds via simple substitution of the solvent by CO to generate the expected mononuclear methyl carbonyl cation [Pd(dippe)Me(CO)]+, followed by migratory insertion to give the acetyl carbonyl derivative [Pd(dippe)(COMe)(CO)]+. The final product is the dinuclear mixed-valence species [Pd(dippe)(μ-CO)Pd(dippe)Me][BAr4], which is accompanied by the formation of acetone (Me2CO) and the dicarbonyl dication [Pd(dippe)(CO)2]2+. Presumably, methyl transfer occurs at some stage from the methyl cation to generate the methyl-acetyl complex, Pd(dippe)Me(COMe); reductive elimination of acetone under CO from the methyl-acetyl complex produces the Pd0 complex Pd(dippe)CO which then reacts with the starting methyl cation to generate the dinuclear mixed-valence species. Addition of CO to the mixed-valence species does not result in formation of mononuclear complexes, rather 1 equivalent of CO adds to form a new dinuclear complex with two bridging COs.
