A one-pot synthesis of ortho-arylated 9-(pyridin-2-yl)-9H-carbazoles via C-H bond activation, in which palladium(II)-catalyzed cross-coupling of 9-(pyridin-2-yl)-9H-carbazoles with potassium aryltrifluoroborates is presented. Silver nitrate and tert-butanol were proved to be the best oxidant and solvent for the process, respectively. The product yields fluctuated from modest to excellent, and the reaction showed sufficient functional group tolerance. p-Benzoquinone served as an important ligand for the transmetalation and reductive elimination steps in the catalytic process. The key intermediate of the reaction, 9-(pyridin-2-yl)-9H-carbazole palladacycle was isolated and confirmed by X-ray crystallography. The kinetic isotope effect (kH/kD) for the C-H bond activation step was measured as 0.87. In addition, Hammett experiment gave a negative rho value, -2.14 with a reasonable correlation (R2 = 0.90). The directing group, pyridyl was demonstrated as a removable functional group. Finally, a rational catalytic mechanism is presented based on all experimental evidence.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0709112-170941 |
| Date | 09 July 2012 |
| Creators | Wu, Chung-chiu |
| Contributors | Jen-Chieh Hsieh, Ming-Jung Wu, Michael Y. Chiang |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0709112-170941 |
| Rights | user_define, Copyright information available at source archive |
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