Influence of the Element and Substituent Effects on the Reactivity of Catching Reactions of Difluorocarbene by Benzene-Bridged and Group-13/Group-15-Based Frustrated Lewis Pairs.

ABSTRACT

The trapping reactions of CF2 by benzene-bridged Group-13/P-based and B/Group-15-based frustrated Lewis pairs (FLPs) have been computationally investigated based on density functional theory. Interestingly, our theoretical calculations predict that the capture of CF2 by all five Group-13/P-based FLPs is energetically feasible. However, in the B/Group-15-based FLPs, only the phosphorus-based B/P-FLP can trap CF2 from kinetic and thermodynamical viewpoints. According to the analyses of the activation strain model, it can be known that the atomic radius of the G15 element (Lewis base) of benzene-bridged B/Group-15-FLP plays an important role in controlling the reactivity of the CF2 catching reactions, whereas the atomic radius of the Group-13 center (Lewis acid) does not play a role in influencing the activation barrier of these CF2 catching reactions. Our theoretical findings based on sophisticated methods suggest that the forward bonding is the FLP-to-CF2 interaction, the LP (Group-15-donor) → vacant p-π-orbital (CF2), which was quantitatively proved to be strong in such present CF2 catching reactions. However, the back bonding is the CF2-to-FLP interaction, the empty σ-orbital (Group-13-acceptor) ← sp2-σ-orbital (CF2), which was verified to be relatively weak. Our theoretical pieces of evidence reveal that the stronger electron-donating ability of the substituents is attached to the Lewis basic center and can make the reaction barrier of the benzene-bridged Group-13/Group-15-based FLP-related compound catching CF2 smaller and more exothermic.