Olefin slippage

Olefin Slippage During Nucleophilic Addition to Alkenes... 

C-H Activation, Part II 723 The Sandmeyer Reaction 726 Olefin Slippage During Nucleophilic Addition to Alkenes 737... 

The changes in structure during this attack are depicted in Equation 11.21. Eisenstein and Hoffmann concluded many years ago that a symmetric metal-olefin complex is deactivated toward nucleophilic attack, but slippage of the olefin creates a LUMO that can interact with the incoming nucleophile. Thus, in the transition state for external attack, "the organometallic olefinic complex cannot be near its equilibrium structure." ... 

A symmetrically r] -coordinated olefin is deactivated to nucleophilic attack thus it should be noted that slippage and deformation to t] -coordination plays a crucial role in activating for the nucleophilic addition (Eq. 2) [20, 30-32]. The theoretical studies predicted that in the slipped r] -coordinated olefin, a lowest unoccupied molecular orbital (LUMO) is lowered in energy and localized on the (3-carbon. The slipping to -coordination enables the interaction with external nucleophile and the transition state would be Tj -like structure. 

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