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Hydroxypalladation Precedes the Rate‐Determining Step in the Wacker Oxidation of Ethene
Author(s) -
Imandi Venkataramana,
Kunnikuruvan Sooraj,
Nair Nisanth N.
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201204342
Subject(s) - wacker process , isomerization , chemistry , kinetics , reductive elimination , aldehyde , catalysis , reaction mechanism , rate determining step , photochemistry , solvent , kinetic energy , reaction rate , kinetic isotope effect , rate equation , ligand (biochemistry) , hydride , computational chemistry , ethylene , organic chemistry , metal , deuterium , biochemistry , physics , receptor , quantum mechanics
The complete reaction mechanism and kinetics of the Wacker oxidation of ethene in water under low [Cl − ], [Pd II ], and [Cu II ] conditions are investigated in this work by using ab initio molecular dynamics. These extensive simulations shed light on the molecular details of the associated individual steps, along two different reaction routes, starting from a series of ligand‐exchange processes in the catalyst precursor PdCl 4 2− to the final aldehyde‐formation step and the reduction of Pd II . Herein, we report that hydroxylpalladation is not the rate‐determining step and is, in fact, in equilibrium. The newly proposed rate‐determining step involves isomerization and follows the hydroxypalladation step. The mechanism proposed herein is shown to be in excellent agreement with the experimentally observed rate law and rate. Moreover, this mechanism is in consensus with the observed kinetic isotope effects. This report further confirms the outer‐sphere ( anti ) hydroxypalladation mechanism. Our calculations also ratify that the final product formation proceeds through a reductive elimination, assisted by solvent molecules, rather than through β‐hydride elimination.