Isolation and reactivity of palladium hydrido complexes: intermediates in the hydrodefluorination of pentafluoropyridine.

The hydrido complexes trans-[Pd(H)(4-C(5)NF(4))(PiPr(3))(2)] (3) and trans-[Pd(H)(4-C(5)NF(4))(PCy(3))(2)] (5) can be prepared by reaction of trans-[Pd(F)(4-C(5)NF(4))(PiPr(3))(2)] (2) or trans-[Pd(F)(4-C(5)NF(4))(PCy(3))(2)] (4) with HBpin (HBpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, pinacolborane). The iodo and triflato complexes trans-[Pd(I)(4-C(5)NF(4))(PiPr(3))(2)] (7) and trans-[Pd(OTf)(4-C(5)NF(4))(PiPr(3))(2)] (9) are generated on treatment of complex 3 with MeI or ethyltrifluoromethanesulfonate (EtOTf), respectively. Treatment of 3 with Ph(3)CPF(6) in MeCN results in the formation of trans-[Pd(4-C(5)NF(4))(NCMe)(PiPr(3))(2)]PF(6) (6a). Heating 3 to 60 degrees C gives the products of reductive elimination 2,3,5,6-tetrafluoropyridine as well as [Pd(PiPr(3))(2)] (1). In the presence of pentafluoropyridine [Pd(PiPr(3))(2)] (1) affords the oxidative addition product 2. In a catalytic experiment, pentafluoropyridine can be converted into 2,3,5,6-tetrafluoropyridine in the presence of HBpin with 44% yield when 10% of 3 is employed as catalyst.