A DFT computational study of the mechanism of butadiene carbonylation catalyzed by palladium complexes

Abstract

A theoretical DFT study of the mechanism of the butadiene carbonylation catalysed by Pd(II) complexes has been carried out. The Pd(PH₃)₂Cl₂ species has been chosen as a model compound to emulate the catalyst. Even if Pd(PH₃)₂Cl₂ can behave, in principle, as catalytic species, leading to both observed products, i.e., methyl 3-pentenoate (linear ester) and methyl 2-methyl-3-butenoate (branched ester), the experimentally observed selectivity for the linear product (about 90%) is not explained by these results. It has been found that the reaction channels involving Pd(PH₃)(CO)Cl₂ and Pd(CO)₂Cl₂ as active catalytic species (these species are likely to form at the experimental conditions of high CO pressure) are favored since they require much lower activation barriers. Also, for both species the path leading to the linear product is highly favoured with respect to the path affording the branched ester. This aspect is particularly evident for Pd(CO)₂Cl₂, which seems to be the real active catalytic species of the process.

Supporting Information of the Paper: A DFT Computational Study of the Mechanism of Butadiene Carbonylation Catalyzed by Palladium(II) Complexes

M. ANGELS CARVAJAL†, GIAN PIETRO MISCIONE‡, ANTONIO ACCARDI‡, JUAN J. NOVOA*† and ANDREA BOTTONI*‡

†Department de Quimica Fisica, Facultat de Quimica, and CERQT, Park Cientific, Universitat de Barcelona, Av. Diagonal 647, 08028-Barcelona, Spain. E-mail: [email protected] ‡Dipartimento do Chimica “G. Ciamician”, Universitat' di Bologna, via Selmi 2, 40126 Bologna, Italy. E-mail: [email protected]

Figure S1. Schematic representation of the structures of TS₁₈, M₁₈, TS₁₉, M₁₉ and TS₂₀. The energies (kcal mol⁻¹) are relative to the non-interacting butadiene, trans-Pd(PH₃)₂Cl₂ and CO (asymptotic limit). E _a E= activation barriers. Bond lengths are in angstroms and angles in degrees. Transition state imaginary frequencies (cm⁻¹) are given in round brackets.

Figure S2. Schematic representation of the structures of M₂₀, TS₂₁, M₂₁ and TS₂₂. The energies (kcal mol⁻¹) are relative to the non-interacting butadiene, trans-Pd(PH₃)₂Cl₂ and CO (asymptotic limit). E _a = activation barriers. Bond lengths are in angstroms and angles in degrees. Transition state imaginary frequencies (cm⁻¹) are given in round brackets.

Acknowledgements

The work was performed under the project HPC-EUROPA (RII3-CT-2003-506079), with the support of the European Community-Research Infrastructure Action under the FP6 “Structuring the European Research Area” Programme.