Cross-coupling allylpalladium chloride dimers

The Hiyama couplings of heterocycles are still being developed to their full potential. Nevertheless, several heteroaryl halides have been cross-coupled with aryl or heteroaryl silicon reagents [52]. For example, in the presence of catalytic tt-allylpalladium chloride dimer and two equivalents of KF, the cross-coupling of ethyl(2-thienyl)difluorosilane (53) and methyl 3-iodo-2-thiophenecarboxylate led to bis-thiophene 54 under relatively forcing conditions [53]. 

The allylpalladium chloride dimer (1) has been widely used as catalyst precursor for various Pd-catalyzed reactions such as allylic alkylations and cross-coupling reactions. It has also found applications in hydrovinylation, hydrosilylation, hyroamination, and reduction reactions. 

Cross-coupling Reactions. The allylpalladium chloride dimer (1) has served as an excellent active catalyst precursor for various cross-coupling reactions. The well-known Mizoroki-Heck reaction was widely exemplified in the presence of the system (1)/-Tedicyp (eq 77). Several aryl bromides were reacted with aryl acrylates, styrenyl or alkenyl derivatives, ethyleneglycol vinyl ether, and alk-l-en-3-ol. 8 This catalytic system was efficient for the coupling of vinyl bromides as well. The catalyst loading can be reduced and the substrate/catalyst ratio could reach 100 000 000 in some cases. 

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