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Mechanistic Insights into the Ni‐Catalyzed Reductive Carboxylation of C−O Bonds in Aromatic Esters with CO 2 : Understanding Remarkable Ligand and Traceless‐Directing‐Group Effects
Author(s) -
Han YanLi,
Zhao BingYuan,
Jiang KunYao,
Yan HuiMin,
Zhang ZhuXia,
Yang WenJing,
Guo Zhen,
Li YanRong
Publication year - 2018
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201800257
Subject(s) - reductive elimination , chemistry , carboxylation , homolysis , oxidative addition , bimetallic strip , catalysis , bond cleavage , ligand (biochemistry) , reactivity (psychology) , medicinal chemistry , combinatorial chemistry , dissociation (chemistry) , carbonylation , stereochemistry , reaction mechanism , deprotonation , photochemistry , radical , organic chemistry , carbon monoxide , medicine , biochemistry , receptor , alternative medicine , pathology , ion
The mechanism of the Ni 0 ‐catalyzed reductive carboxylation reaction of C(sp 2 )−O and C(sp 3 )−O bonds in aromatic esters with CO 2 to access valuable carboxylic acids was comprehensively studied by using DFT calculations. Computational results revealed that this transformation was composed of several key steps: C−O bond cleavage, reductive elimination, and/or CO 2 insertion. Of these steps, C−O bond cleavage was found to be rate‐determining, and it occurred through either oxidative addition to form a Ni II intermediate, or a radical pathway that involved a bimetallic species to generate two Ni I species through homolytic dissociation of the C−O bond. DFT calculations revealed that the oxidative addition step was preferred in the reductive carboxylation reactions of C(sp 2 )−O and C(sp 3 )−O bonds in substrates with extended π systems. In contrast, oxidative addition was highly disfavored when traceless directing groups were involved in the reductive coupling of substrates without extended π systems. In such cases, the presence of traceless directing groups allowed for docking of a second Ni 0 catalyst, and the reactions proceed through a bimetallic radical pathway, rather than through concerted oxidative addition, to afford two Ni I species both kinetically and thermodynamically. These theoretical mechanistic insights into the reductive carboxylation reactions of C−O bonds were also employed to investigate several experimentally observed phenomena, including ligand‐dependent reactivity and site‐selectivity.