Copper-catalyzed azide-alkyne cycloaddition (CuAAC) by functionalized NHC-based polynuclear catalysts: scope and mechanistic insights

González-Lainez, M. ; Gallegos, M. ; Munárriz, J. ; Azpiroz, R. ; Passarelli, V. ; Jiménez, M. V. ; Pérez Torrente, J. J. (Universidad de Zaragoza)

Resumen: Copper(I) Cu2(µ-Br)2(tBuImCH2pyCH2L)]n (L = OMe, NEt2, NHtBu) compounds supported by flexible functionalized NHC-based polydentate ligands have been prepared in a one-pot procedure by reacting the corresponding imidazolium salt with an excess of copper powder and Ag2O. An X-ray diffraction analysis has revealed that Cu2(µ-Br)2(tBuImCH2pyCH2NEt2)]n is a linear coordination polymer formed by bimetallic Cu(µ-Br)]2 units linked by the lutidine-based NHC-py-NEt2 ligand, which acts as a heteroditopic ligand with a 1¿C-2¿2N, N' coordination mode. We propose that the polymeric compounds break down in the solution into more compact tetranuclear Cu2(µ-Br)2(tBuImCH2pyCH2L)]2 compounds with a coordination mode identical to the functionalized NHC ligands. These compounds have been found to exhibit high catalytic activity in the Cu-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. In particular, Cu2(µ-Br)2(tBuImCH2pyCH2NEt2)]2 efficiently catalyzes the click reaction of a range of azides and alkynes, under an inert atmosphere at room temperature in neat conditions at a very low catalyst loading, to quantitatively afford the corresponding 1, 4-disubstituted 1, 2, 3-triazole derivatives in a few minutes. The cycloaddition reaction of benzyl azide to phenylacetylene can be performed at 25-50 ppm catalyst loading by increasing the reaction time and/or temperature. Reactivity studies have shown that the activation of the polynuclear catalyst precursor involves the alkyne deprotonation by the NHC moiety of the polydentate ligand to afford a copper(I)-alkynyl species bearing a functionalized imidazolium ligand. DFT calculations support the participation of the dinuclear species (CuBr)2(µ-tBuImCH2pyCH2NEt2)], resulting from the fragmentation of the tetranuclear compound, as the catalytically active species. The proposed reaction pathway proceeds through zwitterionic dinuclear intermediates and entails the active participation of both copper atoms, as well as the NHC moiety as an internal base, which activates the reacting alkyne via deprotonation.

Idioma: Inglés

DOI: 10.1021/acs.organomet.2c00246

Año: 2022

Publicado en: Organometallics 41, 15 (2022), 2154-2169
ISSN: 0276-7333

Factor impacto JCR: 2.8 (2022)

Categ. JCR: CHEMISTRY, ORGANIC rank: 16 / 52 = 0.308 (2022) - Q2 - T1
Categ. JCR: CHEMISTRY, INORGANIC & NUCLEAR rank: 16 / 42 = 0.381 (2022) - Q2 - T2

Factor impacto CITESCORE: 6.6 - Chemistry (Q1)

Factor impacto SCIMAGO: 0.868 - Inorganic Chemistry (Q1) - Physical and Theoretical Chemistry (Q1) - Organic Chemistry (Q1)

Financiación: info:eu-repo/grantAgreement/ES/AEI/PGC2018-095953-B-I00
Financiación: info:eu-repo/grantAgreement/ES/DGA-FSE/E42-20R
Financiación: info:eu-repo/grantAgreement/ES/MCIU/FPU19-02903
Financiación: info:eu-repo/grantAgreement/ES/MICINN-FEDER/PID2019-103965GB-I00
Financiación: info:eu-repo/grantAgreement/ES/MINECO/BES-2014-069624

Tipo y forma: Article (Published version)

Área (Departamento): Área Química Inorgánica (Dpto. Química Inorgánica)