Hydrodefluorination of a Fluorobenzene Equivalent by Harnessing a P(III)/Pd(II)-P(V)/Pd(0) Redox Couple Using a P-CF3-Functionalized Benzazaphosphole.

A stepwise sequence for the hydrodefluorination of a fluorobenzene equivalent has been described. By utilization of a P(III)/Pd(II)-P(V)/Pd(0) redox couple, pyramidalized P-CF3-functionalized benzazaphosphole 1 accepts Ph-F from Pd(II) complexes B/C, resulting in the formation of trigonal bipyramidal (TBP) 2 featuring new P-Ph and P-F bonds. The desired release of Ph-H and regeneration of trivalent 1 from pentavalent 2 was silane-dependent. Using smaller silanes, fluoride abstraction forms phosphonium cation 3 with a hydridosilicate counterion, which delivers hydride to the cationic P-center, affording TBP analogues of Type 4. These observable P-H derivatives like 4x selectively expel H-CF3 and P-Ph-functionalized 5 via a highly asynchronous transition state, resembling a heterolytic P-CF3 bond cleavage/deprotonation event. If larger silanes like Ph3Si-H are employed, the targeted Ph-H/1 product pair is generated directly from 2, closing the stoichiometric hydrodefluorination process. The P(III)/Pd(II)-P(V)/Pd(0) mechanism, silane-dependent product formation, and loss of H-CF3 from 4x redox reaction were evaluated by DFT calculations.