Arylpalladium phenoxide

The electronic effects on the reductive elimination of aryl ethers from BlNAP-ligated palladium complexes (Eq. 6) was studied by Widenhoefer and Buchwald. Because the reductive elimination of acyclic ethers required activated palladium-bound aiyl groups, the scope of the arylpalladium alkoxide complexes was limited. An example of elimination from an oxametallacycle that contained an unactivated aryl group demonstrated that the formation of cychc ethers may become more general. Nonetheless, studies on these systems showed that the factors that control elimination of ethers are similar to those that control elimination of amines. For example, alkoxide complexes that are more electron rich at the alkoxide oxygen underwent faster reductive elimination than those that are more electron poor. Elimination of diaryl ethers from arylpalladium phenoxides did not occur. 

As part of the studies of ligand effects on the reductive elimination of diaryl ethers, arylpalladium phenoxide complexes containing a DPPF analog that had P-CF3 substituents on each of the ligand aryl groups was prepared. This CF3-DPPF complex underwent reductive elimination of diaryl ether only twice as fast as the simple DPPF complex (Eq. 7). ... 

Steric properties of the ligand have a more pronounced effect on the rate of reductive elimination. Arylpalladium phenoxide complexes containing a stericaUy hindered monophosphine P(Fc)(I-Bu)2 (Fc = ferrocenyl) underwent reductive elimination of diaryl ethers, even when the palladium-bound aryl group was unactivated, as shown in Eq. Arylpalladium phenoxide intermediates containing P(t-Bu)3 as ligand under-... 

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