122210-99-5Relevant articles and documents
Substituent effects on P-C reductive elimination from styrylpalladium(II) phosphine complexes
Wakioka, Masayuki,Ozawa, Fumiyuki
, p. 5570 - 5578 (2011/01/11)
A series of styrylpalladium phosphine complexes, trans-[Pd(CH=CHAr) Br(PMeAr′2)2] (1: Ar = Ph, 4-MeOC6H 4, 4-MeC6H4, 4-F3CC 6H4, 4-O2NC6H4; Ar′ = Ph, 4-MeC6H4, 4-FC6H4), have been prepared, and their P-C reductive elimination in the presence of added PMeAr′2 (1-4 equiv) in CD2Cl2 has been examined by kinetic experiments. All complexes are converted to [Pd(η2-ArCH=CHPMeAr′2)(PMeAr′2) 2]Br (3) at 40 °C in high selectivity. The kinetic data are consistent with the reaction process involving prior association of 1 with PMeAr′2 to form a five-coordinate intermediate, trans-[Pd(CH=CHAr)Br(PMeAr′2)3] (A), which subsequently undergoes P-C reductive elimination to give 3. The pseudo-first-order rate constant (kobsd) increases as the amount of added PMeAr′2 ([PMeAr′2]) increases, according to the equation 1/kobsd = 1/kK[PMeAr′2] + 1/k, where K = [A]/[1][PMeAr′2] and k stands for the rate constant for the conversion of A to 3. The association constant K and the rate constant k exhibit a good Hammett correlation with the σp values of para substituents on the Ar and Ar′ groups, respectively: log(K Y/KH) = [+0.84(3)]σp + 0.02(1) (for Ar groups); log(KY/KH) = [+4.2(4)]Σp + 0.09(7) (for Ar′ groups); log(kY/kH) = [-2.43(9)]σp + 0.01(3) (for Ar groups); [-4.8(4)] Σp-0.11(8) (for Ar′ groups). Thus, the K value increases as the electron-withdrawing ability of para substituents increases, while the k value increases as the electron-donating ability of para substituents increases. The P-C reductive elimination mechanism from A to 3 is discussed.
Reaction of trans-Pd(styryl)Br(PMePh2)2 with styryl bromide affording 1,4-diphenyIbutadiene. An unexpected homocoupling process induced by P-C reductive elimination
Wakioka, Masayuki,Nagao, Masato,Ozawa, Fumiyuki
, p. 602 - 608 (2009/01/31)
Reaction of (Z)-styryl bromide (1) with PhB(OH)2 in toluene at 80 °C for 1 h in the presence of Pd(PPh3)4 (1.5 mol %) and an aqueous solution of K2CO3 (3 equiv) affords (Z)-stilbene as the cross-coupling product in 99% yield. On the other hand, the same reaction of the (E)-isomer of 1 forms considerable amounts of homocoupling products (1,4-diphenylbutadiene (2, 22%) and biphenyl (27%)) in addition to the cross-coupling product ((E)-stilbene, 73%). The formation of 2 was examined by kinetic experiments using trans-Pd(CH=CHPh)Br(PMePh2)2 (3) as a model of the presumed intermediate. Complex 3 reacts with 1 at 50 °C for 5 h, giving 2 (91%) and irans-PdBr2(PMePh2) 2 (4, 92%), together with a small amount of Pd(η2- PhCH=CHPMePh2)Br(PMePh2) (5, 8%). The reaction rate shows firstorder dependence on the concentration of 3 and 5, respectively, but is independent of the concentration of 1. A novel homocoupling process induced by P-C reductive elimination from 3 giving 5 is proposed.
Solid-state distortions of nominally square-planar palladium and platinum (R3P)2MX2 complexes as determined by a combination of 13C{1H} and 31P{1H} NMR spectroscopy
Rahn, Jeffrey A.,O'Donnell, Daniel J.,Palmer, Allen R.,Nelson, John H.
, p. 2631 - 2635 (2008/10/08)
Phosphorus-31 and carbon-13 NMR spectra have been obtained for a series of 20 (R3P)2MX2 complexes (R3P = MePh2P and Me2PhP; M = Pd, Pt; X = Cl, Br, I, CN, N3) in the solid state by cross-polarization and magic-angle-spinning (CP/MAS) techniques. Comparison of these data with spectral data obtained at 300 K in CDCl3 solutions was made in order to investigate the influence of local symmetry on 31P and 13C chemical shifts in the solid state. It was found that most of these compounds, which have regular square-planar geometries in solution, are distorted in the solid state. The solid-state distortions are evidenced by additional 31P and 13C resonances in the CP/MAS spectra as compared to the solution spectra. The nature and degree of these distortions are discussed.
