Polymorphism in a secondary phosphine.

Two crystal structures of bis(2,3,5,6-tetramethylphenyl)phosphine, C20H27P, are reported constituting the first recorded case of polymorphism in a secondary phosphine (R2PH). The two structures differ in their conformation and, as a result, the steric hindrance experienced at the phosphorus centre is observed to be dependent on the packing environment. Each polymorph exhibits a distinct supramolecular structure; in polymorph I the molecules are arranged in columns in two directions, whereas polymorph II forms layers. There is a distinct lack of significant intermolecular interactions in either form, with the exception of some weak Me...π interactions observed in polymorph II. These interactions are likely the cause of the variation in the C-P-C angles observed between the two structures.