Bis(phosphazenyl)phosphines: From Superbases to Superhydrides

By incorporating phosphazenes as substituents on phosphines and employing rigid cage-like scaffolds, pentacyclo 5.4.0.02,6.03,10.05.9undecane, pentacyclo 6.4.0.02,7.03,11.06,10 dodecane, and seco-dodecahedradiene, we designed and computationally investigated proton-sponge-like bisphosphines that act as exceptionally strong hydride donors in their monoprotonated forms. These systems exhibit hydricities that significantly surpass that of the paradigmatic superhydride LiEt3BH, one of the strongest commercially available hydride donors widely used in organic reductions. The remarkable hydride-donating ability of these systems originates from strongly electron-donating phosphazenyl substituents at phosphorus, which stabilize the dication formed upon hydride release, as well as from a stabilizing intramolecular dative P→P interaction within the bisphosphine framework. In addition, the neutral forms of the corresponding bisphosphines are shown to exhibit superbasic properties.