期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 127, 期 42, 页码 14817-14824出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja053195p
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资金
- NIGMS NIH HHS [R01 GM63540, R01 GM063540, R01 GM063540-05] Funding Source: Medline
A kinetic investigation into the origin of enantioselectivity for the Pd[(-)-sparteine]Cl-2-catalyzed aerobic oxidative kinetic resolution (OKR) is reported. A mechanism to account for a newly discovered chloride dissociation from Pd[(-)-sparteine]Cl-2 prior to alcohol binding is proposed. The mechanism includes (1) chloride dissociation from Pd[(-)-sparteine]Cl-2 to form cationic Pd(-)-sparteine]Cl, (2) alcohol binding, (3) deprotonation of Pd-bound alcohol to form a Pd-alkoxide, and (4) beta-hydride elimination of Pd-alkoxide to form ketone product and a Pd-hydride. Utilizing the addition of (-)-sparteine HCl to control the [Cl-] and [H+] and the resulting derived rate law, the key microscopic kinetic and thermodynamic constants were extracted for each enantiomer of sec-phenethyl alcohol. These constants allow for the successful simulation of the oxidation rate in the presence of exogenous (-)-sparteine HCl. A rate law for oxidation of the racemic alcohol was derived that allows for the successful prediction of the experimentally measured k(rel) values when using the extracted constants. Besides a factor of 10 difference between the relative rates of beta-hydride elimination for the enantiomers, the main enhancement in enantiodetermination results from a concentration effect of (-)-sparteine HCl and the relative rates of reprotonation of the diastereomeric Pd-alkoxides.
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