On the use of non-symmetrical mixed PCN and SCN pincer palladacycles as catalyst precursors for the Heck reaction

The mixed pincer palladacycles (Me2NCH2 (Cl)C = CCH2CH2Y-kappaN,kappaC,kappaY)PdCl (1, Y = PPh2; 2, OPPh2) and (t-BuSCH2CH2C = C(Cl)(o-NC5H4)- kappaS,kappaC,kappaN)PdCl 3 have been obtained in high yields by chloropalladation of heterosusbstituted alkynes Me2NCH2C = CCH2CH2PPh2, Me2NCH2C = CCH2CH2 OPPh2 and t-BuSCH2CH2C = C(o-NC5H4), respectively. The molecular structures of 1 and 3 have been ascertained by means of X-ray diffraction analysis. The catalytic properties of these mixed donor group pincer-type palladacycles have been evaluated in the arylation of olefins (Heck reaction). The pincer palladacycle 1 is highly active for the coupling of aryl iodides and aryl bromides with n-butyl acrylate. In contrast it is only moderately active for the coupling of aryl chlorides substituted with electron-withdrawing groups and inactive for the coupling of electron neutral and electron deactivated aryl chlorides.