Mechanistic and kinetic insights into the double alkoxycarbonylation of butadiene toward dimethyl adipate

• DFT and experiments reveal the mechanism for the double alkoxycarbonylation of butadiene. • The base-assisted pathway is the only way to explain the selectivity toward the linear product. • Thermodynamic monoesters distribution issued from isomerization limits second alkoxycarbonylation. • Combination of p-TsOH with a base leads to the best compromise in alcoholysis-regeneration steps. The Pd-catalyzed double alkoxycarbonylation of 1,3-butadiene (BD) offers a promising route to adipate esters. Controlling the selectivity toward the linear ester, dimethyl adipate (DMA) is of particular interest to produce adipic acidic. However, the mechanistic foundations and the impact of reaction conditions (such as the acid-base balance) remain unclear. In the present work, we combine kinetic experiments and density functional theory (DFT) calculations to elucidate the reaction mechanism catalyzed by [Pd(d t bpx)H] + and propose a rational interpretation of the acid/base cooperative effects. The isomerization of pentenoate intermediates proceeds through a weakly activated Pd–H-mediated pathway but thermodynamically favors methyl trans -2-pentenoate ( trans -2MP), which dominates the monoester equilibrium in absence of CO. However, the presence of CO and base in the medium makes isomerization the kinetic limiting step controlling the overall catalytic turnover and retarding DMA formation. By using an implicit mixed-solvation model, the DFT simulation reveals that a base-assisted methanolysis pathway is consistent with the observed activity and high linear selectivity, unlike the classical base-free mechanism. These findings reconcile theoretical and experimental insights, uncovering the true kinetic bottleneck of the reaction and guiding the rational optimization of Pd-catalyzed isomerizing alkoxycarbonylation for efficient adipate synthesis