Organometallics 2014-02-01

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

Barbara Procacci, RobinJ Blagg, RobinN Perutz, Nuria Rend__n, AdrianC Whitwood

Index: Organometallics 33(1) , 45-52, (2014)

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Abstract

Irradiation of CpRh(PMe3)(C2H4) (1; Cp = _(5)-C5H5) in the presence of pentafluoropyridine in hexane solution at low temperature yields an isolable _(2)-C,C-coordinated pentafluoropyridine complex, CpRh(PMe3)(_(2)-C,C-C5NF4) (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(PMe3)(C5NF4)H (3). In contrast, UV irradiation of 1 in hexane, in the presence of 4-substituted tetrafluoropyridines C5NF4X, where X = NMe2, OMe, results in elimination of C2H4 and HF to form the metallacycles CpRh(PMe3)(_(2)-C,C-CH2N(CH3)C5NF3) (4) and CpRh(PMe3)(_(2)-C,C-CH2OC5NF3) (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(PMe3)(Ph)H with the respective pyridines at 50 _C.