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

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.