Substituent Effects on P-C Reductive Elimination from Styrylpalladium(II) Phosphine Complexes

作者：Wakioka Masayuki; Ozawa Fumiyuki^*

来源：Organometallics, 2010, 29(21): 5570-5578.

DOI：10.1021/om100476z

A series of styrylpalladium phosphine complexes, trans-[Pd(CH=CHAr)Br(PMeAr'(2))2] (1: Ar = Ph, 4-MeOC(6)H(4), 4-MeC(6)H(4), 4-F(3)CC(6)H(4), 4-O(2)NC(6)H(4); Ar' = Ph, 4-MeC(6)H(4), 4-FC(6)H(4)), have been prepared, and their P-C reductive elimination in the presence of added PMeAr'(2) (1-4 equiv) in CD(2)Cl(2) has been examined by kinetic experiments. All complexes are converted to (Pd(eta(2)-ArCH=CHPMeAr'(2))(PMeAr'(2))(2)]Br (3) at 40 degrees 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 (k(obsd)) increases as the amount of added PMeAr'(2) ([PMeAr'(2)) increases, according to the equation 1/k(obsd) = 1/k K[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 sigma(p) values of pant substituents on the Ar and Ar' groups, respectively: log(K(Y)/K(H)) = [+0.84(3)sigma(p) + 0.02(1) (for Ar groups); log(K(Y)/K(H)) = [+4.2(4)]Sigma sigma(p) + 0.09(7) (for Ar' groups); log(k(Y)/k(H)) = [-2.43(9)]sigma(p) + 0.01(3) (for Ar groups); [-4.8(4)]Sigma sigma(p) - 0.11(8) (for A' groups). Thus, the K value increases as the electron-withdrawing ability of pant substituents increases, while the k value increases as the electron-donating ability of pant substituents increases. The P-C reductive elimination mechanism from A to 3 is discussed.

• 出版日期2010-11-8