Bis-Phenoxo-Cu<sup>II</sup><sub>2</sub> Complexes: Formal Aromatic Hydroxylation via Aryl-Cu<sup>III</sup> Intermediate Species
Ullmann-type copper-mediated arylC-O bond formation has attracted the attention of the catalysis and organometallic communities, although the mechanism of these copper-catalyzed coupling reactions remains a subject of debate. We have designed well-defined triazamacrocyclic-based aryl-Cu<sup>II...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2020-10-01
|
| Series: | Molecules |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1420-3049/25/20/4595 |
| _version_ | 1797551493174263808 |
|---|---|
| author | Xavi Ribas Raül Xifra Xavier Fontrodona |
| author_facet | Xavi Ribas Raül Xifra Xavier Fontrodona |
| author_sort | Xavi Ribas |
| collection | DOAJ |
| description | Ullmann-type copper-mediated arylC-O bond formation has attracted the attention of the catalysis and organometallic communities, although the mechanism of these copper-catalyzed coupling reactions remains a subject of debate. We have designed well-defined triazamacrocyclic-based aryl-Cu<sup>III</sup> complexes as an ideal platform to study the C-heteroatom reductive elimination step with all kinds of nucleophiles, and in this work we focus our efforts on the straightforward synthesis of phenols by using H<sub>2</sub>O as nucleophile. Seven well-defined aryl-Cu<sup>III</sup> complexes featuring different ring size and different electronic properties have been reacted with water in basic conditions to produce final bis-phenoxo-Cu<sup>II</sup><sub>2</sub> complexes, all of which are characterized by XRD. Mechanistic investigations indicate that the reaction takes place by an initial deprotonation of the NH group coordinated to Cu<sup>III</sup> center, subsequent reductive elimination with H<sub>2</sub>O as nucleophile to form phenoxo products, and finally air oxidation of the Cu<sup>I</sup> produced to form the final bis-phenoxo-Cu<sup>II</sup><sub>2</sub> complexes, whose enhanced stability acts as a thermodynamic sink and pushes the reaction forward. Furthermore, the corresponding triazamacrocyclic-Cu<sup>I</sup> complexes react with O<sub>2</sub> to undergo 1e<sup>−</sup> oxidation to Cu<sup>II</sup> and subsequent C-H activation to form aryl-Cu<sup>III</sup> species, which follow the same fate towards bis-phenoxo-Cu<sup>II</sup><sub>2</sub> complexes. This work further highlights the ability of the triazamacrocyclic-Cu<sup>III</sup> platform to undergo aryl-OH formation by reductive elimination with basic water, and also shows the facile formation of rare bis-phenoxo-Cu<sup>II</sup><sub>2</sub> complexes. |
| first_indexed | 2024-03-10T15:45:53Z |
| format | Article |
| id | doaj.art-8cc942710a0d4e27bb18435712b42305 |
| institution | Directory Open Access Journal |
| issn | 1420-3049 |
| language | English |
| last_indexed | 2024-03-10T15:45:53Z |
| publishDate | 2020-10-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Molecules |
| spelling | doaj.art-8cc942710a0d4e27bb18435712b423052023-11-20T16:26:11ZengMDPI AGMolecules1420-30492020-10-012520459510.3390/molecules25204595Bis-Phenoxo-Cu<sup>II</sup><sub>2</sub> Complexes: Formal Aromatic Hydroxylation via Aryl-Cu<sup>III</sup> Intermediate SpeciesXavi Ribas0Raül Xifra1Xavier Fontrodona2Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, Campus Montilivi, E-17003 Girona, Catalonia, SpainInstitut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, Campus Montilivi, E-17003 Girona, Catalonia, SpainServeis Tècnics de Recerca (STR), Universitat de Girona, Parc Científic i Tecnològic, E-17003 Girona, Catalonia, SpainUllmann-type copper-mediated arylC-O bond formation has attracted the attention of the catalysis and organometallic communities, although the mechanism of these copper-catalyzed coupling reactions remains a subject of debate. We have designed well-defined triazamacrocyclic-based aryl-Cu<sup>III</sup> complexes as an ideal platform to study the C-heteroatom reductive elimination step with all kinds of nucleophiles, and in this work we focus our efforts on the straightforward synthesis of phenols by using H<sub>2</sub>O as nucleophile. Seven well-defined aryl-Cu<sup>III</sup> complexes featuring different ring size and different electronic properties have been reacted with water in basic conditions to produce final bis-phenoxo-Cu<sup>II</sup><sub>2</sub> complexes, all of which are characterized by XRD. Mechanistic investigations indicate that the reaction takes place by an initial deprotonation of the NH group coordinated to Cu<sup>III</sup> center, subsequent reductive elimination with H<sub>2</sub>O as nucleophile to form phenoxo products, and finally air oxidation of the Cu<sup>I</sup> produced to form the final bis-phenoxo-Cu<sup>II</sup><sub>2</sub> complexes, whose enhanced stability acts as a thermodynamic sink and pushes the reaction forward. Furthermore, the corresponding triazamacrocyclic-Cu<sup>I</sup> complexes react with O<sub>2</sub> to undergo 1e<sup>−</sup> oxidation to Cu<sup>II</sup> and subsequent C-H activation to form aryl-Cu<sup>III</sup> species, which follow the same fate towards bis-phenoxo-Cu<sup>II</sup><sub>2</sub> complexes. This work further highlights the ability of the triazamacrocyclic-Cu<sup>III</sup> platform to undergo aryl-OH formation by reductive elimination with basic water, and also shows the facile formation of rare bis-phenoxo-Cu<sup>II</sup><sub>2</sub> complexes.https://www.mdpi.com/1420-3049/25/20/4595organometallic Cu<sup>III</sup>C-O cross couplingphenol synthesisphenoxo-bridged Cu<sup>II</sup> complexesaromatic hydroxylationcopper |
| spellingShingle | Xavi Ribas Raül Xifra Xavier Fontrodona Bis-Phenoxo-Cu<sup>II</sup><sub>2</sub> Complexes: Formal Aromatic Hydroxylation via Aryl-Cu<sup>III</sup> Intermediate Species Molecules organometallic Cu<sup>III</sup> C-O cross coupling phenol synthesis phenoxo-bridged Cu<sup>II</sup> complexes aromatic hydroxylation copper |
| title | Bis-Phenoxo-Cu<sup>II</sup><sub>2</sub> Complexes: Formal Aromatic Hydroxylation via Aryl-Cu<sup>III</sup> Intermediate Species |
| title_full | Bis-Phenoxo-Cu<sup>II</sup><sub>2</sub> Complexes: Formal Aromatic Hydroxylation via Aryl-Cu<sup>III</sup> Intermediate Species |
| title_fullStr | Bis-Phenoxo-Cu<sup>II</sup><sub>2</sub> Complexes: Formal Aromatic Hydroxylation via Aryl-Cu<sup>III</sup> Intermediate Species |
| title_full_unstemmed | Bis-Phenoxo-Cu<sup>II</sup><sub>2</sub> Complexes: Formal Aromatic Hydroxylation via Aryl-Cu<sup>III</sup> Intermediate Species |
| title_short | Bis-Phenoxo-Cu<sup>II</sup><sub>2</sub> Complexes: Formal Aromatic Hydroxylation via Aryl-Cu<sup>III</sup> Intermediate Species |
| title_sort | bis phenoxo cu sup ii sup sub 2 sub complexes formal aromatic hydroxylation via aryl cu sup iii sup intermediate species |
| topic | organometallic Cu<sup>III</sup> C-O cross coupling phenol synthesis phenoxo-bridged Cu<sup>II</sup> complexes aromatic hydroxylation copper |
| url | https://www.mdpi.com/1420-3049/25/20/4595 |
| work_keys_str_mv | AT xaviribas bisphenoxocusupiisupsub2subcomplexesformalaromatichydroxylationviaarylcusupiiisupintermediatespecies AT raulxifra bisphenoxocusupiisupsub2subcomplexesformalaromatichydroxylationviaarylcusupiiisupintermediatespecies AT xavierfontrodona bisphenoxocusupiisupsub2subcomplexesformalaromatichydroxylationviaarylcusupiiisupintermediatespecies |