Leaving Group Assistance in the La<sup>3+</sup>-Catalyzed Cleavage of Dimethyl (<i>o</i>-Methoxycarbonyl)aryl Phosphate Triesters in Methanol
作者:David R. Edwards、C. Tony Liu、Graham E. Garrett、Alexei A. Neverov、R. Stan Brown
DOI:10.1021/ja904659e
日期:2009.9.30
cleavage of the phosphate triesters with poor leaving groups relative to those with good leaving groups and (2) it provides an increase in cleavage rate relative to those of comparable substrates that do not have that functional group, e.g., k2(La)(dimethyl o-(methoxycarbonyl)phenyl phosphate)/k2(La)(dimethyl phenyl phosphate) = 60. Activation parameters for the La3+(2)-catalyzed methanolysis of 4a and dimethyl
在含有不同浓度 La3+ 和 (s)(s) 的甲醇中,在 25 摄氏度下研究了一系列芳基含有邻甲氧基羰基 (o-CO2Me) 取代基 (4a-i) 的二甲基芳基磷酸酯三酯的催化甲醇分解)pH。La3+(2) 催化的底物 4a(二甲基(邻甲氧基羰基)苯基磷酸酯)裂解的二阶速率常数的测定作为(s)(s)pH 的函数根据物种形成图进行评估,该图显示该过程由 La3+(2)(-OCH3)x 二聚体催化,其中 x = 1-5,所有物种之间的活性差异仅为 5 倍。4a-i 在 (s)(s)pH 8.7 下催化甲醇分解的二级催化速率常数 (k2(La)) 符合 log k2(La) = (-0.82 +/- 0.11) 的布朗斯泰德关系( s)(s)pKa(lg) + (11.61 +/- 1.48),其中梯度比一系列不含 o-CO2Me 取代基的二甲基芳基磷酸酯测定的梯度更浅,log k2(La) =