期刊
CHEMICAL SCIENCE
卷 2, 期 2, 页码 326-330出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c0sc00392a
关键词
-
资金
- National Science Foundation [CHE-0543585]
- [CHE-0840494]
- [TG-CHE-070040]
The reaction of molecular oxygen with palladium(II)-hydrides is a key step in Pd-catalyzed aerobic oxidation reactions, and the mechanism of such reactions has been the focus of considerable investigation and debate. Here we describe the reaction of O-2 with a series of electronically varied Pd-II-H complexes of the type trans-(IMes)(2)Pd(H)(O2CAr), with different para-substituted benzoates as the ArCO2- ligand. Analysis of the oxygenation rates of these complexes revealed a non-linear Hammett plot, and further kinetic studies demonstrated that reaction of O-2 with the most electron-rich para-methoxybenzoate derivative proceeds via two parallel mechanisms, one initiated by rate-limiting reductive elimination of the carboxylic acid (HXRE) and the other involving hydrogen-atom abstraction by O-2 (HAA). DFT computational studies support these conclusions and reveal that the preferred mechanism for the O-2 insertion reaction changes from HAA to HXRE as the para substituent on the benzoate ligand shifts from electron-donating to electron-withdrawing.
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