Highly Active, Air-Stable Palladium Catalysts for the C−C and C−S Bond-Forming Reactions of Vinyl and Aryl Chlorides: Use of Commercially Available [(t-Bu)2P(OH)]2PdCl2, [(t-Bu)2P(OH)PdCl2]2, and [[(t-Bu)2PO···H···OP(t-Bu)2]PdCl]2 as Catalysts

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Abstract
Air-stable palladium complexes [(t-Bu)2P(OH)]2PdCl2, [(t-Bu)2P(OH)PdCl2]2, and [[(t-Bu)2PO···H···OP(t-Bu)2]PdCl]2 serve as efficient catalysts for a variety of cross-coupling reactions of vinyl and aryl chlorides with arylboronic acids, arylzinc reagents, and thiols to yield the corresponding styrene derivatives, biaryls, and thioethers. 31P NMR and mechanistic studies argue that the phosphinous acid ligands in the complexes can be deprotonated in the presence of a base to yield an electron-rich anionic species, which is likely a catalyst intermediate, and dimeric [[(t-Bu)2PO···H···OP(t-Bu)2]PdCl]2 was isolated and cystallographically characterized. These anionic complexes are anticipated not only to accelerate the rate-determining oxidative addition of aryl chlorides but also to stabilize the palladium complexes in the catalytic cycle.