1233923-53-9Relevant 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.
