To provide a scientific detailed understanding of the mechanism of activation of hydrogen using FLPs, this part is going to introduce the molecular orbital interactions in the reaction system, using the t Bu3P/B(C6F5)3 pair as an example. The main steps of the reaction are indicated in Figure . An FLP intermediate is formed. For the formation of the dative adduct, the HOMO of Lewis acid has an obvious interaction with LUMO of Lewis base, whereas there is not any reaction in the case of FLPs and the orbital interaction in FLPs is respectively weak.