The palladium-catalyzed conversion of (bio)pentenoic acid isomers (PEAs) occurs with high activity and selectivity to adipic acid (ADA) in the presence of the diphosphine ligand L₂ = 1,2-bis[(di-tert-butyl)phosphinomethyl]benzene (DTBPX) and an acid cocatalyst. Using density functional theory (DFT) calculations, we show that the active catalyst ([L₂Pd^II-H]⁺) isomerizes the PEAs to their equilibrium mixture, from which selective carbonylation and hydrolysis results in the ADA product. Hydrolysis is the rate-limiting and also selectivity-determining step, consisting of two parts, hydration and “product release”. After the separation of ADA from Pd(0), the product is in a hydrate form. The conversion of this Pd(0) species to the active catalyst occurs quickly with an acid cocatalyst. This conclusion is also supported by the experimental finding that a moderate acidity increases the overall reaction rate. The bulky P substituents in the DTBPX ligand largely prevent chelation of the pending COOH moiety of PEAs, thus allowing the same high regioselectivity as is obtainable with unfunctionalized long-chain alkenes. We also modeled the CO insertion into the chelate complexes and confirmed an increase of more than 50 kJ mol^–1 in the barrier for their conversion.

中文翻译：

---

钯催化戊烯酸的羟羰基化。催化选择性的计算和实验研究

在二膦配体L ₂ = 1,2-双[（二叔丁基）的存在下，钯催化的（生物）戊烯酸异构体（PEA）的转化具有很高的活性和对己二酸（ADA）的选择性。膦甲基]苯（DTBPX）和酸助催化剂。使用密度泛函理论（DFT）计算，我们表明活性催化剂（[L ₂ Pd ^II -H] ⁺）将PEA异构化为它们的平衡混合物，由此选择性羰基化和水解生成ADA产物。水解是限速和决定选择性的步骤，由水合和“产物释放”两部分组成。将ADA与Pd（0）分离后，产物为水合物形式。这种Pd（0）物质向活性催化剂的转化在酸性助催化剂的作用下迅速发生。实验发现也证明了这一结论，适度的酸性提高了总反应速率。DTBPX配体中庞大的P取代基很大程度上防止了PEA的未决COOH部分的螯合，因此可实现与未官能化长链烯烃相同的区域选择性。^–1阻碍了他们的conversion依。