Hydrodefluorination of a Fluorobenzene Equivalent by Harnessing a P(III)/Pd(II)–P(V)/Pd(0) Redox Couple Using a P–CF 3 -Functionalized Benzazaphosphole

Résumé fourni par la source

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–CF 3 -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–CF 3 and P–Ph-functionalized 5 via a highly asynchronous transition state, resembling a heterolytic P–CF 3 bond cleavage/deprotonation event. If larger silanes like Ph 3 Si–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–CF 3 from 4x redox reaction were evaluated by DFT calculations.

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