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Exploring the Oxidative‐Addition Pathways of Phenyl Chloride in the Presence of Pd II Abnormal N‐Heterocyclic Carbene Complexes: A DFT Study
Author(s) -
Mondal Totan,
De Sriman,
Maity Bholanath,
Koley Debasis
Publication year - 2016
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.201602735
Subject(s) - chemistry , reductive elimination , oxidative addition , catalysis , carbene , palladium , dissociation (chemistry) , medicinal chemistry , transition state , activation energy , photochemistry , organic chemistry
DFT calculations were performed to elucidate the oxidative addition mechanism of the dimeric palladium(II) abnormal N‐heterocyclic carbene complex 2 in the presence of phenyl chloride and NaOMe base under the framework of a Suzuki–Miyaura cross‐coupling reaction. Pre‐catalyst 2 undergoes facile, NaOMe‐assisted dissociation, which led to monomeric palladium(II) species 5 , 6 , and 7 , each of them independently capable of initiating oxidative addition reactions with PhCl. Thereafter, three different mechanistic routes, path a, path b, and path c, which originate from the catalytic species 5 , 7 , and 6 , were calculated at M06‐ L ‐D3(SMD)/LANL2TZ(f)(Pd)/6–311++G**//M06‐L/LANL2DZ(Pd)/6–31+G* level of theory. All studied routes suggested the rather uncommon Pd II /Pd IV oxidative addition mechanism to be favourable under the ambient reaction conditions. Although the Pd 0 /Pd II routes are generally facile, the final reductive elimination step from the catalytic complexes were energetically formidable. The Pd II /Pd IV activation barriers were calculated to be 11.3, 9.0, 26.7 kcal mol −1 (ΔΔ ≠ G L S‐D3 ) more favourable than the Pd II /Pd 0 reductive elimination routes for path a, path b, and path c, respectively. Out of all the studied pathways, path a was the most feasible as it comprised of a Pd II /Pd IV activation barrier of 24.5 kcal mol −1 (Δ G L S‐D3 ). To further elucidate the origin of transition‐state barriers, EDA calculations were performed for some key saddle points populating the energy profiles.