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) A, the first example of measurement of such a distance at cyclopentadienyl rhodium(III).