An unusually stable chlorophosphite: What makes BIFOP-Cl so robust against hydrolysis?

Two chlorophosphites, the biphenyl-based BIFOP-Cl and the diphenyl ether-based O-BIFOP-Cl, exhibit striking differences regarding their reaction with water. While BIFOP-Cl is nearly completely unreactive, its oxo-derivative O-BIFOP-Cl reacts instantly with water, yielding a tricyclic hydrocarbon unit after rearrangement. The analysis of the crystal structure of O-BIFOP-Cl and BIFOP-Cl revealed that the large steric demand of encapsulating fenchane units renders the phosphorus atom nearly inaccessible by nucleophilic reagents, but only for BIFOP-Cl. In addition to the steric effect, a hypervalent P(III)-O interaction as well as an electronic conjugation effect causes the high reactivity of O-BIFOP-Cl. A DFT study of the hydrolysis in BIFOP-Cl verifies a higher repulsive interaction to water and a decreased leaving tendency of the chloride nucleofuge, which is caused by the fenchane units. This high stability of BIFOP-Cl against nucleophiles supports its application as a chiral ligand, for example, in Pd catalysts.