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‐κN,κC,κY)PdCl ( 1 , Y=PPh₂; 2 , OPPh₂) and (t‐BuSCH₂CH₂CC(Cl)(o‐NC₅H₄)‐κS,κC,κN)PdCl 3 have been obtained in high yields by chloropalladation of heterosusbstituted alkynes Me₂NCH₂CCCH₂CH₂PPh₂, Me₂NCH₂CCCH₂CH₂OPPh₂ 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.