Photochemical Reactions of Fluorinated Pyridines at Half-Sandwich Rhodium Complexes: Competing Pathways of Reaction.

Irradiation of CpRh(PMe)(CH) (; Cp = η-CH) in the presence of pentafluoropyridine in hexane solution at low temperature yields an isolable η-Ccoordinated pentafluoropyridine complex, CpRh(PMe)(η-,CNF) (). The molecular structure of was determined by single-crystal X-ray diffraction, showing coordination by C3-C4, unlike previous structures of pentafluoropyridine complexes that show N-coordination. Corresponding experiments with 2,3,5,6-tetrafluoropyridine yield the C-H oxidative addition product CpRh(PMe)(CNF)H (). In contrast, UV irradiation of in hexane, in the presence of 4-substituted tetrafluoropyridines CNFX, where X = NMe, OMe, results in elimination of CH and HF to form the metallacycles CpRh(PMe)(κ-,-HN(CH)CNF) () and CpRh(PMe)(κ-,-HOCNF) (), respectively. The X-ray structure of shows a planar RhCCNC-five-membered ring. Complexes - may also be formed by thermal reaction of CpRh(PMe)(Ph)H with the respective pyridines at 50 °C.