Chan–Evans–Lam Couplings with Copper Iminoarylsulfonate Complexes: Scope and Mechanism

Chan–Evans–Lam Couplings with Copper Iminoarylsulfonate Complexes: Scope and Mechanism

Copper­(II) pyridyliminoarylsulfonate complexes with chloride or triflate counteranions were employed in Chan–Evans–Lam (CEL) couplings of N-nucleophiles and arylboronic acids. The complexes avoided typical side reactions in CEL couplings, and an excess of boronic acid was not required. Water was to...

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Bibliographic Details
Published in:ACS catalysis Vol. 8; no. 8; pp. 7308 - 7325
Main Authors: Hardouin Duparc, Valérie, Bano, Guillaume L, Schaper, Frank
Format: Journal Article
Language:English
Published: American Chemical Society 03-08-2018
Subjects:
C−N bond formation
Chan−Evans−Lam coupling
homogeneous catalysis
copper coordination complexes
mechanism
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Summary:Copper­(II) pyridyliminoarylsulfonate complexes with chloride or triflate counteranions were employed in Chan–Evans–Lam (CEL) couplings of N-nucleophiles and arylboronic acids. The complexes avoided typical side reactions in CEL couplings, and an excess of boronic acid was not required. Water was tolerated, and addition of neither base nor other additives was necessary. Primary amines, acyclic and cyclic secondary amines, anilines, aminophenol, imidazole, pyrazole, and phenyltetrazole can be quantitatively arylated at either 25 or 50 °C with 2.5 mol % of the catalyst. Reaction kinetics were investigated in detail. Kinetic and spectroscopic studies provide evidence for the formation of unproductive copper–substrate complexes. Formation of an aniline–phenylboronic acid adduct was responsible for the zero-order dependence of reaction rates on phenylboronic acid concentration. Kinetic evidence indicates that the order of reaction steps is transmetalation, nucleophile coordination, and oxidation. Couplings performed poorly with electron-deficient arylboronic acids, due to a slower Cu­(II)/Cu­(III) oxidation in the catalytic cycle. Photoredox catalysis partially resolved this problem, but addition of copper acetate as an external oxidant proved to be more efficient.
ISSN:2155-5435
2155-5435
DOI:10.1021/acscatal.8b01881