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

[Image: see text] Irradiation of CpRh(PMe(3))(C(2)H(4)) (1; Cp = η(5)-C(5)H(5)) in the presence of pentafluoropyridine in hexane solution at low temperature yields an isolable η(2)-C,C-coordinated pentafluoropyridine complex, CpRh(PMe(3))(η(2)-C,C-C(5)NF(4)) (2). The molecular structure of 2 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(3))(C(5)NF(4))H (3). In contrast, UV irradiation of 1 in hexane, in the presence of 4-substituted tetrafluoropyridines C(5)NF(4)X, where X = NMe(2), OMe, results in elimination of C(2)H(4) and HF to form the metallacycles CpRh(PMe(3))(κ(2)-C,C-CH(2)N(CH(3))C(5)NF(3)) (4) and CpRh(PMe(3))(κ(2)-C,C-CH(2)OC(5)NF(3)) (5), respectively. The X-ray structure of 4 shows a planar RhCCNC-five-membered ring. Complexes 2–5 may also be formed by thermal reaction of CpRh(PMe(3))(Ph)H with the respective pyridines at 50 °C.