Interaction between Spirosilanes and Lewis Bases: from Coordination to Frustration.

In this work we describe the interaction between Lewis bases, especially N-Heterocyclic Carbenes (NHCs), and hindered neutral silicon derivatives featuring high Lewis acid properties. It has been established that the formation of normal and abnormal Lewis adducts can be controlled by playing with the acidity of the corresponding tetravalent spiro organosilane. Some DFT calculations have been performed in order to gain insight into the thermodynamics of the NHC-spirosilane interaction featuring various NHCs differing in size and σ-donor capacity. In a second part, we have studied the possibility of introducing spirosilanes as new Lewis partners in FLP chemistry. Some FLP-type reactivities are presented, notably the activation of formaldehyde that could occur with both hindered NHCs and phosphines.