389798-53-2Relevant 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)+.
