Chromium-Salen Catalyzed Cross-Coupling of Phenols: Mechanism and Origin of the Selectivity

A highly chemoselective phenol cross-coupling reaction catalyzed by a Cr-salen catalyst was developed. Kinetic studies showed that the oxidation of Cr­(III) to Cr­(V) is the rate-determining step of the reaction. In addition, experimental stoichiometric analysis showed that a high valent Cr­(V) spec...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2019-06, Vol.141 (25), p.10016-10032
Main Authors: Nieves-Quinones, Yexenia, Paniak, Thomas J, Lee, Young Eun, Kim, Sun Min, Tcyrulnikov, Sergei, Kozlowski, Marisa C
Format: Article
Language:English
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Summary:A highly chemoselective phenol cross-coupling reaction catalyzed by a Cr-salen catalyst was developed. Kinetic studies showed that the oxidation of Cr­(III) to Cr­(V) is the rate-determining step of the reaction. In addition, experimental stoichiometric analysis showed that a high valent Cr­(V) species is the active catalyst for this process. The selectivity of the reaction was found to be determined by the cross-coupling carbon–carbon bond forming reaction, rather than any precoordination species. It appears that the lowest energy cross-coupling pathway requires a lesser degree of electronic reorganization in its transition state vs the lowest energy homocoupling pathway. This result was supported by stoichiometric Cr­(V) kinetics, 13C kinetic isotope effects, and density functional theory (DFT) calculations. The understanding of the full landscape of this reaction allowed us to develop a general analysis to predict the regioselectivity of the cross-coupling reaction.
ISSN:0002-7863
1520-5126
DOI:10.1021/jacs.9b03890