PHOTOCHEMICAL DISPLACEMENT OF COORDINATED ETHENE FROM [RH(ETA(5)-C5H5)(PPH3)(C2H4)]

The rhodium (triphenylphosphine)(ethene) complex [Rh(eta(5)-C5H5)(PPh3 )(C2H4)], was synthesized by reaction of [{Rh(C2H4)(2)Cl}(2)] with tri phenylphosphine and thallium cyclopentadienide. Like in [Rh(eta(5)-C5H 5)(PMe3)(C2H4)], the co-ordinated ethene ligand may be displaced photo chemically. Photoreaction of [Rh(eta(5)-C5H5)(PPh3)(C2H4)] with SiR3H (R = Pr-i or Et) and hexafluorobenzene yielded [Rh(eta(5)-C5H5)(PPh3)( SiR3)H] and [Rh(eta(5)-C5H5)(PPh3)(eta(2)-C6F6)], respectively. Oxidat ive addition of the C-H bonds of partially fluorinated arenes, C6F5H a nd 1,3-C6F2H4, was demonstrated by NMR spectroscopy to result in forma tion of [Rh(eta(5)-C5H5)(PPh3)(R)H] (R = C6F5 or 2,6-C6F2H3). Oxidativ e addition of benzene may be detected following photolysis in benzene- thf mixtures at 233 K, but the product decomposes on warming. The mole cular structure of [Rh(eta(5)-C5H5)(PPh3)(SiPr3i)H] has been determine d crystallographically. The disorder of the isopropyl groups was model led with two orientations of the SiPr3i with equal occupancies. The Rh -Si bond length is 2.386(2) Angstrom, the first example of measurement of such a distance at cyclopentadienyl rhodium(III).