Combined Experimental and Computational Mechanistic Investigation of the Palladium-Catalyzed Decarboxylative Cross-Coupling of Sodium Benzoates with Chloroarenes

Reported
herein is a mechanistic investigation into the palladium-catalyzed
decarboxylative cross-coupling of sodium benzoates and chloroarenes.
The reaction was found to be first-order in Pd. A minimal substituent
effect was observed with respect to chloroarene, and the reaction
was zero-order with respect to chloroarene. Palladium-mediated decarboxylation
was assigned as the turnover-limiting step based on an Eyring plot
and density functional theory computations. Catalyst performance was
found to vary based on the electrophile, which is best explained by
catalyst decomposition at Pd(0). The 1,5-cyclooctadiene (COD) ligand
contained in the precatalyst CODPd­(CH2TMS)2 (Pd1) was shown to be a beneficial additive. The bench-stable
Buchwald complex XPhosPdG2 could be used with exogenous
COD and 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl
(XPhos) instead of complex Pd1. Adding exogenous XPhos
significantly increased the catalyst turnover number and enhanced
reproducibility.