Intramolecular and supramolecular geometry of coordinated PPh3

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Abstract
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.

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