Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies
Cationic palladium(II) complexes have been found to be highly reactive towards aromatic C–H activation of arylureas at room temperature. A commercially available catalyst [Pd(MeCN)4](BF4)2 or a nitrile-free cationic palladium(II) complex generated in situ from the reaction of Pd(OAc)2 and HBF4, effe...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Beilstein-Institut
2016-05-01
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| Series: | Beilstein Journal of Organic Chemistry |
| Subjects: | |
| Online Access: | https://doi.org/10.3762/bjoc.12.99 |
| _version_ | 1831671260386426880 |
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| author | Takashi Nishikata Alexander R. Abela Shenlin Huang Bruce H. Lipshutz |
| author_facet | Takashi Nishikata Alexander R. Abela Shenlin Huang Bruce H. Lipshutz |
| author_sort | Takashi Nishikata |
| collection | DOAJ |
| description | Cationic palladium(II) complexes have been found to be highly reactive towards aromatic C–H activation of arylureas at room temperature. A commercially available catalyst [Pd(MeCN)4](BF4)2 or a nitrile-free cationic palladium(II) complex generated in situ from the reaction of Pd(OAc)2 and HBF4, effectively catalyzes C–H activation/cross-coupling reactions between aryl iodides, arylboronic acids and acrylates under milder conditions than those previously reported. The nature of the directing group was found to be critical for achieving room temperature conditions, with the urea moiety the most effective in promoting facile coupling reactions at an ortho C–H position. This methodology has been utilized in a streamlined and efficient synthesis of boscalid, an agent produced on the kiloton scale annually and used to control a range of plant pathogens in broadacre and horticultural crops. Mechanistic investigations led to a proposed catalytic cycle involving three steps: (1) C–H activation to generate a cationic palladacycle; (2) reaction of the cationic palladacycle with an aryl iodide, arylboronic acid or acrylate, and (3) regeneration of the active cationic palladium catalyst. The reaction between a cationic palladium(II) complex and arylurea allowed the formation and isolation of the corresponding palladacycle intermediate, characterized by X-ray analysis. Roles of various additives in the stepwise process have also been studied. |
| first_indexed | 2024-12-19T23:31:48Z |
| format | Article |
| id | doaj.art-2e3539d08dbd431083e70a9a8cbe76d4 |
| institution | Directory Open Access Journal |
| issn | 1860-5397 |
| language | English |
| last_indexed | 2024-12-19T23:31:48Z |
| publishDate | 2016-05-01 |
| publisher | Beilstein-Institut |
| record_format | Article |
| series | Beilstein Journal of Organic Chemistry |
| spelling | doaj.art-2e3539d08dbd431083e70a9a8cbe76d42022-12-21T20:01:42ZengBeilstein-InstitutBeilstein Journal of Organic Chemistry1860-53972016-05-011211040106410.3762/bjoc.12.991860-5397-12-99Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studiesTakashi Nishikata0Alexander R. Abela1Shenlin Huang2Bruce H. Lipshutz3Department of Chemistry & Biochemistry, University of California, Santa Barbara, CA 93106, USADepartment of Chemistry & Biochemistry, University of California, Santa Barbara, CA 93106, USADepartment of Chemistry & Biochemistry, University of California, Santa Barbara, CA 93106, USADepartment of Chemistry & Biochemistry, University of California, Santa Barbara, CA 93106, USACationic palladium(II) complexes have been found to be highly reactive towards aromatic C–H activation of arylureas at room temperature. A commercially available catalyst [Pd(MeCN)4](BF4)2 or a nitrile-free cationic palladium(II) complex generated in situ from the reaction of Pd(OAc)2 and HBF4, effectively catalyzes C–H activation/cross-coupling reactions between aryl iodides, arylboronic acids and acrylates under milder conditions than those previously reported. The nature of the directing group was found to be critical for achieving room temperature conditions, with the urea moiety the most effective in promoting facile coupling reactions at an ortho C–H position. This methodology has been utilized in a streamlined and efficient synthesis of boscalid, an agent produced on the kiloton scale annually and used to control a range of plant pathogens in broadacre and horticultural crops. Mechanistic investigations led to a proposed catalytic cycle involving three steps: (1) C–H activation to generate a cationic palladacycle; (2) reaction of the cationic palladacycle with an aryl iodide, arylboronic acid or acrylate, and (3) regeneration of the active cationic palladium catalyst. The reaction between a cationic palladium(II) complex and arylurea allowed the formation and isolation of the corresponding palladacycle intermediate, characterized by X-ray analysis. Roles of various additives in the stepwise process have also been studied.https://doi.org/10.3762/bjoc.12.99arylationcationic palladiumC–H functionalizationgreen chemistryolefination |
| spellingShingle | Takashi Nishikata Alexander R. Abela Shenlin Huang Bruce H. Lipshutz Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies Beilstein Journal of Organic Chemistry arylation cationic palladium C–H functionalization green chemistry olefination |
| title | Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies |
| title_full | Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies |
| title_fullStr | Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies |
| title_full_unstemmed | Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies |
| title_short | Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies |
| title_sort | cationic pd ii catalyzed c h activation cross coupling reactions at room temperature synthetic and mechanistic studies |
| topic | arylation cationic palladium C–H functionalization green chemistry olefination |
| url | https://doi.org/10.3762/bjoc.12.99 |
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