Computational Overview of a Pd-Catalyzed Olefin Bis-alkoxycarbonylation Process

Abstract

A comprehensive density functional theory analysis is reported for the one-pot bis-alkoxycarbonylation reaction of olefins to form succinic acid esters by action of the catalyst (N-N)­Pd­(TFA)2 (N-N = bis­(2,6-dimethylphenyl)-2,3-dimethyl-1,4-diazabutadiene, TFA– = CF3CO2 –). The selective and efficient process involves alkene (H2C=CHR), CO, methanol, and p-benzoquinone (BQ) molecules as reactants. The catalytic mechanism, previously proposed on the basis of available experimental and literature data, is critically revised here. A plethora of optimized intermediates and transition states and their correlating energy profiles allow a step by step reconstruction of the entire cycle, highlighting key mechanistic aspects, such as the role of the R substituent in the olefin. One of its effects is determined by the presence of a 2e – donor group, which, depending on its power, may affect the catalysis up to its total inhibition. As another aspect, the key diester product forms through a reductive elimination step (Pd­(II) → Pd(0) transformation) that excludes the previously proposed attainment of a Pd­(II)–hydride complex. Finally, the paper illustrates the action of the sacrificial BQ oxidant in the restoration of the original Pd­(II) catalyst, as found for other strictly related cases. The energy profile indicates that the rate-determining step occurs in the initial part of the reaction, given a +29.6 kcal mol–1 energy barrier, associated with a methoxo migration into an adjacent CO ligand. The result foreshadows a rather slow activation of the catalyst and a long duration of the cycle.

Multiwavelets applied to metal–ligand interactions: Energies free from basis set errors

“…We have build our test set to include ligands of various size, many of which are common incoming ligands in metal-catalyzed reactions (such as H2, CO, alkenes, methanol). 3,4,5,6,7,8,9,10 Several features are observed from our computed results (Figure 2, see also SI, Figure S1 to S4). Firstly, the magnitude of the BSSE is largest for DZ basis sets, with an average value of 9.92 kcal/mol for the 26 kcal/mol).…”

“…1,2 Many of the studied reactions involve metal complexes that throughout the course of the reaction bind or lose a ligand, for example, there may be incoming substrates such as alkenes or hydrogen (H2), or leaving ligands such as solvent or product molecules (Scheme 1). 3,4,5,6,7,8,9,10 The difficulty of contemporary DFT functionals to accurately compute metal-ligand interactions has been highlighted in the literature. 11,12,13,14,15,16,17,18,19,20,21,22 Many of the reported studies focus on the performance of different DFT functionals and the importance of including dispersion corrections in the computed energies.…”

Study on Rh(I)/Ru(III) Bimetallic Catalyst Catalyzed Carbonylation of Methanol to Acetic Acid

“…In the Monsanto catalyst, to avoid the deactivation of the catalyst active metal Rh when the CO partial pressure is low, a large amount of water is usually added. We investigated the effect of water content on the performance of the bimetallic catalyst in the methanol carbonylation reaction [ 31 , 32 , 33 ]. Figure 8 shows the performance of Rh(I)/Ru(III) bimetallic catalyst catalyzed carbonylation of methanol under different H 2 O mass fractions.…”

Combined Effect of Palladium Catalyst and the Alcohol to Promote the Uncommon Bis‐Alkoxycarbonylation of Allylic Substrates

“…[22b,35] Complex A reacts with the alcohol allowing the formation of the intermediate B, where the displaced TFA À anion interacts with the alcohol linked to the palladium through an hydrogen bonding. [36] This facilitates the formation of the alkoxycarbonyl-palladium complex C, in which the first molecule of CO is inserted. [37] The subsequent coordination and insertion of allyl acetate 2 a in complex C produces the 5-membered palladacycle D [38] and a second CO insertion leads to the formation of the 6-membered palladacycle E. [39] This latter complex can be in equilibrium with other open-chain species, bearing the TFA or a CO molecule linked to the Pd, in place of the PdÀ O bond.…”