Temperature-dependent transitions between normal and inverse equilibrium isotope effects for coordination and oxidative addition of C-H and H-H bonds to a transition metal center.
Temperature-dependent transitions between normal and inverse equilibrium isotope effects for coordination and oxidative addition of C-H and H-H bonds to a transition metal center.
复制标题
正平衡和逆平衡同位素之间的温度依赖性转变对 C-H 和 H-H 键与过渡金属中心的配位和氧化加成产生影响。
DOI：
10.1021/ja034559l
复制
发表时间：
2003
影响因子：
15
通讯作者：
G. Parkin
中科院分区：
文献类型：
--
作者：
K. E. Janak;G. Parkin
用密度泛函理论(B3LYP)计算确定了新钨物种[[H_2Si(C_5H_4)_2]W}与C-H和H-H键配位和氧化加成的平衡同位素效应与温度的关系。CH4和CD4配位的EIE并不表现出典型的Van‘t Hoff型行为，即EIE随温度单调变化；相反，EIE的温度依赖关系呈现最大值，在低温下呈倒数(<；1)，在高温下呈正值(>；1)。CH4和D2氧化加成反应的EIE对温度的依赖关系与配位反应明显不同，EIE在所有温度下都是正常的，并且在0K接近无穷大。与所有温度下正常的甲烷氧化加成反应相反，H2和D2氧化加成反应的EIE随着温度的升高表现出从反向到正常的转变。在低温下，这些体系中存在的逆电子是由于同位素取代时产物的零点能量变化大于反应物(H2或CH4)的零点能量变化的结果。
The temperature dependence of the equilibrium isotope effects (EIEs) for coordination and oxidative addition of C-H and H-H bonds to the tungstenocene species {[H2Si(C5H4)2]W} has been determined with the aid of DFT (B3LYP) calculations. The EIE for coordination of CH4 and CD4 does not exhibit typical van't Hoff type behavior in which there is a monotonic variation of EIE with temperature; rather, the temperature dependence of the EIE exhibits a maximum, with inverse values (<1) at low temperature and normal values (>1) at high temperatures. The temperature dependence of the EIE for oxidative addition of CH4 and CD4 differs significantly from that for coordination, with the EIE being normal at all temperatures and approaching infinity at 0 K. In contrast to oxidative addition of methane which is normal at all temperatures, the EIE for oxidative addition of H2 and D2 exhibits a transition from inverse to normal upon raising the temperature. The existence of inverse EIEs in these systems at low temperatures is a result of the zero point energy changes for the products upon isotopic substitution being greater than those for the reactants (H2 or CH4).