Reactivity Models of Hydrogen Activation by Frustrated Lewis Pairs: Synergistic Electron Transfers or Polarization by Electric Field?

详细信息    查看全文

• 作者：Tibor Andr谩s Rokob ; Imre Bak贸 ; Andr谩s Stirling ; Andrea Hamza ; Imre P谩pai
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：March 20, 2013
• 年：2013
• 卷：135
• 期：11
• 页码：4425-4437
• 全文大小：712K
• 年卷期：v.135,no.11(March 20, 2013)
• ISSN：1520-5126

文摘

Two alternative qualitative reactivity models have recently been proposed to interpret the facile heterolytic cleavage of H₂ by frustrated Lewis pairs (FLPs). Both models assume that the reaction takes place via reactive intermediates with preorganized acid/base partners; however, they differ in the mode of action of the active centers. In the electron transfer (ET) model, the hydrogen activation is associated with synergistic electron donation processes with the simultaneous involvement of active centers and the bridging hydrogen, showing similarity to transition-metal-based and other H₂-activating systems. In contrast, the electric field (EF) model suggests that the heterolytic bond cleavage occurs as a result of polarization by the strong EF present in the cavity of the reactive intermediates. To assess the applicability of the two conceptually different mechanistic views, we examined the structural and electronic rearrangements as well as the EFs along the H₂ splitting pathways for a representative set of reactions. The analysis reveals that electron donations developing already in the initial phase are general characteristics of all studied reactions, and the related ET model provides qualitative interpretation for the main features of the reaction pathways. On the other hand, several arguments have emerged that cast doubt on the relevance of EF effects as a conceptual basis in FLP-mediated hydrogen activation.