Photochemical displacement of co-ordinated ethene from [Rh(η5-C5H5)(PPh3)(C2H4)]

Abstract

The rhodium (triphenylphosphine)(ethene) complex [Rh(η⁵-C₅H₅)(PPh₃)(C₂H₄)], was synthesized by reaction of [{Rh(C₂H₄)₂Cl}₂] with triphenylphosphine and thallium cyclopentadienide. Like in [Rh(η⁵-C₅H₅)(PMe₃)(C₂H₄)], the co-ordinated ethene ligand may be displaced photochemically. Photoreaction of [Rh(η⁵-C₅H₅)(PPh₃)(C₂H₄)] with SiR₃H (R = Prⁱ or Et) and hexafluorobenzene yielded [Rh(η⁵-C₅H₅)(PPh₃)(SiR₃)H] and [Rh(η⁵-C₅H₅)(PPh₃)(η²-C₆F₆)], respectively. Oxidative addition of the C–H bonds of partially fluorinated arenes, C₆F₅H and 1,3-C₆F₂H₄, was demonstrated by NMR spectroscopy to result in formation of [Rh(η⁵-C₅H₅)(PPh₃)(R)H] (R = C₆F₅ or 2,6-C₆F₂H₃). Oxidative addition of benzene may be detected following photolysis in benzene–thf mixtures at 233 K, but the product decomposes on warming. The molecular structure of [Rh(η⁵-C₅H₅)(PPh₃)(SiPrⁱ₃)H] has been determined crystallographically. The disorder of the isopropyl groups was modelled with two orientations of the SiPrⁱ₃ with equal occupancies. The Rh–Si bond length is 2.386(2) Å, the first example of measurement of such a distance at cyclopentadienyl rhodium(III).