100898-97-3Relevant academic research and scientific papers
Facile chloropalladation of vinylcyclopropanes. Isolation of ring-opened 1,2,5-η3-σ,π chelates as kinetic precursors to 1-3-η3-π-allyl final products
Parra-Hake, Miguel,Rettig, Michael F.,Williams, Jimmie L.,Wing, Richard M.
, p. 1032 - 1040 (2008/10/08)
Reactions of vinylcyclopropane (1a), isopropenylcyclopropane (1c), and α-cyclopropyl-4-fluorostyrene (1d) (all are vinylcyclopropanes) with PdCl2(PhCN)2 in low polarity aprotic media (e.g., CDCl3) leads to rapid cyclopropane chloropalladation with formation of 1,2,5-η3-σ,π chelates. In one case (1a) the precursor to chloropalladation - a π complex that may involve Pd(II)-cyclopropane interaction also - is observed by 1H and 13C NMR. The 1,2,5-η3-σ,π complexes rearrange in solution over periods of hours to days to 1-3-η3-π-allyls. In the case of the 1,2,5-η3-σ,π complex from 1a, namely, 6, allyl formation is accompanied by rearrangement (hydrogen shift). Compound 6 rearranges to a π-allyl also in the solid state, but in this case the hydrogen shift path is not followed. Dynamic NMR experiments conducted on 6 lead to the conclusion that very fast chloropalladation/dechloropalladation occurs in solution, in such a way that the carbon alternately getting and losing chlorine dynamically inverts its configuration. This observation leads to a better understanding of earlier published results for chrysanthemate ester isomerizations catalyzed by PdCl2(PhCN)2. In the course of the present work, the molecular structures of the following two compounds were determined by X-ray diffraction: bis(μ-chloro)bis(1,2,5-η 3-2-methyl-3-chloro-1-penten-5-yl)di-palladium(II) (5) and (acetylacetonato)(1-3-η 3-2-methyl-5-chloro-1-penten-3-yl)palladium(II) (9). Crystal data for compound 5: space group P1 (no. 2); a = 5.487 (3) A?, b = 11.959 (2) A?, c = 6.902 (2) A?; α = 89.06 (2)°, β = 107.2 (3)°, γ = 106.3 (3)°; V = 414.1 (5) A?3; Z = 2. The refinement for 5 was based on 1263 reflections with I > 3σ(I) with a final R = 3.4% and Rw = 5.2%. Crystal data for compound 9: space group P21/c (no. 14); a = 4.529 (2) A?, b = 17.026 (3) A?, c = 16.580 (3) A?; β = 92.49 (3)°; V = 1277 (1) A?3; Z = 4. The refinement for 9 was based on 1740 reflections with I > 3σ(I) with final R = 3.4% and Rw = 4.4%.
