Structural and conformational analysis of a biaryl phosphine integrating a calix[4]arene cavity. Can the phosphorus atom behave as an introverted donor?

The conformational preference of a cavity-based biaryl phosphine, namely 5-(2-diphenylphosphinyl-phenyl)-25,26,27,28-tetrapropyloxycalix[4]arene (L) has been investigated by density functional theory calculations. The analysis showed that the barrier to rotation about the C-C axle of the biaryl unit is only 10.7 kcal mol(-1), this rendering possible access to conformers of two types, those in which the P lone pair sits at the cavity entrance and points to the calixarene interior, others with a more open structure where the P atom is located outside the cavity. As revealed by a single crystal X-ray diffraction study, the biaryl phosphine appears virtually as an atropisomer in the solid state in which the phosphorus atom lies totally out of the cavity defined by the four phenoxy rings.

Automated summary

This study investigated the conformational preference of a cavity-based biaryl phosphine, 5-(2-diphenylphosphinyl-phenyl)-25,26,27,28-tetrapropyloxycalix[4]arene (L), through density functional theory calculations. The analysis revealed that the rotation barrier of the biaryl unit around the C-C axis is only 10.7 kcal mol(-1), allowing the existence of two types of conformers: one with the P lone pair inside the cavity pointing to the calixarene interior, and the other with a more open structure where the P atom is located outside the cavity. Single crystal X-ray diffraction study showed that the biaryl phosphine is essentially an atropisomer in the solid state, with the phosphorus atom completely out of the cavity defined by the four phenoxy rings.