Intramolecular and supramolecular geometry of coordinated PPh3

We report an analysis of the M-PPh3 groups in the Cambridge Structural Database. About 60% of the 8663 characterised M-PPh3 groups do not exhibit the conformation of a threefold rotor. The M-PPh3 moiety occurs with a variety of conformations for the phenyl rings, ranging from the expected threefold rotor, through conformations where the phenyl rings are parallel or orthogonal to the P-M vector, to conformations where two rings have approximately equal and opposite M-P-C-C torsional angles and are like a flipper rather than a rotor. There are two sub-groups of flipper, in which the third phenyl ring is either approximately parallel or orthogonal to the P-M vector. The rotor conformation of M-PPh3, and both forms of the flipper conformation, are capable of forming the sixfold phenyl embrace (6PE), in which all six phenyl rings participate, but only the rotor-6PE possesses the concerted cycle of six local edge-to-face Ph ... Ph interactions. The occurrence of fourfold phenyl embraces in M-PPh3 compounds is also investigated. Calculated supramolecular energies are presented: a pair of embracing PPh3 ligands has a strong supramolecular attractive energy, ranging from -11 to -5 kcal mol(-1).