Pan Zhengzheng, Horner John H, Newcomb Martin
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, USA.
J Am Chem Soc. 2008 Jun 25;130(25):7776-7. doi: 10.1021/ja802484n. Epub 2008 May 31.
Rate constants for oxidations of benzyl alcohol-d0 and -d7 by oxoiron(IV) tetramesitylporphyrin radical cation perchlorate in acetonitrile were measured in single turnover kinetic studies. The kinetic isotope effect (kH/kD) increased from 28 at 23 degrees C to 360 at -30 degrees C due to extensive hydrogen atom tunneling that was analyzed in terms of a parabolic energy barrier to tunneling. Similarly, large KIE values were found for oxidations of ethylbenzene-d0 and -d10 at room temperature. The large KIE values are a function of the porphyrin identity, and porphyrins containing electron-withdrawing groups display normal KIEs. KIEs found under catalytic turnover conditions are somewhat smaller than those obtained in single turnover reactions. The results should serve as benchmarks for computational studies of C-H oxidations by porphyrin and heme-iron-oxo systems.
在单周转动力学研究中，测定了四（均三甲苯基）卟啉高氯酸盐铁（IV）氧代物在乙腈中氧化苄醇-d0和-d7的速率常数。由于广泛的氢原子隧穿，动力学同位素效应（kH/kD）从23℃时的28增加到-30℃时的360，这种隧穿根据抛物线形隧穿能垒进行了分析。同样，在室温下，乙苯-d0和-d10氧化反应也发现了较大的动力学同位素效应值。较大的动力学同位素效应值是卟啉特性的函数，含有吸电子基团的卟啉显示出正常的动力学同位素效应值。在催化周转条件下发现的动力学同位素效应值略小于单周转反应中获得的值。这些结果应作为卟啉和血红素-铁-氧代体系C-H氧化计算研究的基准。
