Poli Rinaldo, Harvey Jeremy N
Laboratoire de Synthèse et d'Electrosynthèse Organométalliques, Faculté de Sciences 'Gabriel', Université de Bourgogne, 6 Boulevard Gabriel, 21100 Dijon, France.
Chem Soc Rev. 2003 Jan;32(1):1-8. doi: 10.1039/b200675h.
Many reactions of transition metal compounds involve a change in spin. These reactions may proceed faster, slower--or at the same rate as--otherwise equivalent processes in which spin is conserved. For example, ligand substitution in [CpMo(Cl)2(PR3)2] is faster than expected, whereas addition of dinitrogen to [CpMo(Cl)(PMe3)2] is slow. Spin-forbidden oxidative addition of ethylene to [CpIr(PMe3)] occurs competitively with ligand association. To explain these observations, we discuss the shape of the different potential energy surfaces (PESs) involved, and the energy of the minimum energy crossing points (MECPs) between them. This computational approach is of great help in understanding the mechanisms of spin-forbidden reactions, provided that accurate calculations can be used to predict the relevant PESs. Density functional theory, especially using gradient-corrected and hybrid functionals, performs reasonably well for the difficult problem of predicting the energy splitting between different spin states of transition metal complexes, although careful calibration is needed.
许多过渡金属化合物的反应涉及自旋的变化。这些反应可能比自旋守恒的其他等效过程进行得更快、更慢或速率相同。例如，[CpMo(Cl)2(PR3)2]中的配体取代比预期的要快，而向[CpMo(Cl)(PMe3)2]中添加二氮则很慢。乙烯与[CpIr(PMe3)]的自旋禁阻氧化加成与配体缔合竞争发生。为了解释这些观察结果，我们讨论了所涉及的不同势能面（PES）的形状，以及它们之间的最小能量交叉点（MECP）的能量。只要能使用精确计算来预测相关的PES，这种计算方法对于理解自旋禁阻反应的机理有很大帮助。密度泛函理论，特别是使用梯度校正和杂化泛函，对于预测过渡金属配合物不同自旋态之间的能量分裂这一难题表现得相当不错，不过需要仔细校准。
