Journal
ACS CATALYSIS
Volume 12, Issue 3, Pages 1809-1817Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.1c00247
Keywords
palladium catalysis; cross-coupling; vinyl carboxylates; DFT studies; reaction mechanism
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Funding
- Hoffmann Institute of Advanced Materials at Shenzhen Polytechnic
- University of Colorado Denver
- National Natural Science Foundation of China [21773139]
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This study investigates the detailed working mechanism of a notable base-free cross-coupling reaction using density functional theory. It reveals that the reaction proceeds through a complex Pd(0)/Pd(II) pathway and elucidates the dual role of an arylboronic acid as a reducing agent and coupling partner. These mechanistic insights have important implications for new reaction development.
There is continued interest in developing new Pd-catalyzed cross-coupling reactions. This density functional theory (DFT) study explores the detailed workings of a notable base-free cross-coupling reaction of vinyl carboxylates with arylboronic acids at ambient conditions enabled by Pd(OAc)(2) along with a phosphine ligand. Extensive DFT calculations have been performed on the proposed Pd(II)-only mechanism and other possibilities, suggesting that the reaction preferably proceeds by a Pd(0)/Pd(II) pathway with an intricate Pd(0)-generating process. Two consecutive transmetalations with phenylboronic acid lead to a diphenyl-Pd(II) phosphine intermediate, which would undergo a phenyl-phenyl reductive elimination rather than a redox-neutral carbopalladation. The resulting Pd(0) phosphine species introduces a Pd(0)/Pd(II) catalytic cycle involving the key elementary steps of oxidative addition, transmetalation, and reductive elimination. The oxidative addition of the vinyl carboxylate to Pd(0) via R-OAc bond cleavage is the rate-determining step. The dual role of an arylboronic acid as a reducing agent and coupling partner in Pd-catalyzed cross-coupling reactions has been elucidated for the first time. This and other mechanistic insights gained can have implications for new reaction development.
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