Ring-Opening of THF via an Intramolecular P/Al-Based Frustrated Lewis Pair: Assistance by C6F5 Groups beyond Electronegativity?

A frustrated Lewis pair composed of an acidic aluminum function (AlR2) and a basic phosphine entity, linked by a xanthene spacer, is capable of cleaving THF. The rate of the ring-opening reaction is higher by a factor of 10 for R = C6F5 than that for R = Mes. Structural and theoretical investigations revealed for the case of C6F5 aromatic interactions in the secondary coordination sphere which-in case they also exist in the transition state-could aid ring-opening through a preorientation of the reacting functions. However, in detailed computational studies these were found to occur without contributing significantly to the lowering of the activation barrier.

Automated summary

The frustrated Lewis pair consisting of an acidic aluminum function and a basic phosphine entity linked by a xanthene spacer can cleave THF. The rate of the ring-opening reaction is 10 times higher for R = C6F5 compared to R = Mes, but computational studies show that aromatic interactions in the secondary coordination sphere do not significantly contribute to lowering the activation barrier.