Contrasting reactivity of fluoropyridines at palladium and platinum: C-F oxidative addition at palladium, P-C and C-F activation at platinum

The divergent behavior of palladium(0) and platinum(0) is revealed in the reactivity of [M(PR3)(2)] (M = Pd or Pt; R = Cy or Pr-i) toward pentafluoropyridine and 2,3,5,6-tetrafluoropyridine. The palladium complexes react with pentafluoropyridine at 100 degreesC to yield the fluoride complexes trans- [Pd(F)(4-C5NF4)(PR3)(2)]. They do not react with 2,3,5,6-tetrafluoropyridine. The reaction of platinum(0) complexes [Pt(PR3)(2)] with pentafluoropyridine in THF at ambient temperature yields trans- [Pt(R)(4-C5NF4)(PR3)(PFR2)] complexes, whereas the reaction of [Pt(PCy3)(2)] with 2,3,5,6-tetrafluoropyridine results in C-H activation to form cis- [Pt(H)(4-C5NF4)(PCY3)(2)]; this complex may be converted to the trans isomer by photolysis. The cis-hydride also forms during the reaction of [Pt(PCY3)(2)] with C5NF5 in hexane. These reactions also contrast with earlier studies of the reactivity of the same substrates toward [Ni(PEt3)(2)], which yield [Ni(F)(2-C5NF5)(PEt3)(2)] with pentafluoropyridine and [Ni(F)(2-C5NF4H)(PEt3)(2)] with tetrafluoropyridine. Thus palladium has different regioselectivity from nickel and is the least reactive. Platinum is capable of both C-F and C-H activation and is alone in the triad in undergoing rearrangement to the alkyl complex with the fluorophosphine ligand. Mechanisms for the rearrangement are proposed. The platinum dibydride complex trans-[Pt(H)(2)(PR3)(2)] reacts with pentafluoropyridine at room temperature, yielding a 1: 1: 1 mixture of trans- [PtH(FHF)(PR3)(2)], trans-[Pt(H)(4-C5NF4)(PR3)(2)], and trans[Pt(R)(4-C5NF4)(PR3)(PFR2)]. Crystal structures are reported for trans- [Pd(F)(4-C5NF4)(PCy3)(2)] .H2O.C6H6, trans-[Pd(F)(4-C5NF4)((PPr3)-Pr-i)(2)], trans-[Pt(C6H11)(4-C5NF4)(PCy3)(PFCy2)]. CH2Cl2, and cis- [Pt(H)(4-C5NF4)(PCy3)(2)].