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

Abstract

The hydrido complexes trans-[Pd(H)(4-C₅NF₄)(PiPr₃)₂] (3) and trans-[Pd(H)(4-C₅NF₄)(PCy₃)₂] (5) can be prepared by reaction of trans-[Pd(F)(4-C₅NF₄)(PiPr₃)₂] (2) or trans-[Pd(F)(4-C₅NF₄)(PCy₃)₂] (4) with HBpin (HBpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, pinacolborane). The iodo and triflato complexes trans-[Pd(I)(4-C₅NF₄)(PiPr₃)₂] (7) and trans-[Pd(OTf)(4-C₅NF₄)(PiPr₃)₂] (9) are generated on treatment of complex 3 with MeI or ethyltrifluoromethanesulfonate (EtOTf), respectively. Treatment of 3 with Ph₃CPF₆ in MeCN results in the formation of trans-[Pd(4-C₅NF₄)(NCMe)(PiPr₃)₂]PF₆ (6a). Heating 3 to 60 °C gives the products of reductive elimination 2,3,5,6-tetrafluoropyridine as well as [Pd(PiPr₃)₂] (1). In the presence of pentafluoropyridine [Pd(PiPr₃)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.