Intramolecular dehydrofluorinative coupling of η5-pentamethyleyclopentadienyl and pentafluorophenylphosphine ligands in rhodium complexes

The rhodium(III) complex [Cp*RhCl(dfppe)]BF4, 1, undergoes rapid stepwise intramolecular dehydrofluorinative carbon-carbon coupling on addition of proton sponge to produce [{eta(5),kappaP,kappaP-C5Me3[CH2C6F4-2-P(C6F5)CH2](2)-1,3}RhCI]BF4. The reaction requires less than the stoichiometric, quantity of proton sponge and also occurs on addition of (Bu4NF)-N-n or in the presence of polymer-supported fluoride. NMR studies of reactions between a series of complexes and proton sponge have revealed the necessary conditions for intramolecular dehydrofluorinative coupling in pentamethyleyclopentadienyl rhodium(III) phosphine complexes. The complex must be cationic, and the phosphine, which can be either part of a chelating ligand or monodentate need have only one pentafluorophenyl substituent. The reaction is rapid where Cp* and C6F5 are held in close proximity. The compounds [Cp*RhCl{(C6F5)(2)PC6H4SMe-2}]BF4,7, and the diastereoisomer of [Cp*RhCl{(C6F5)PhPC6H4SMe-2}]BF4, 11a, in which Cp* and C6F5 are cis, undergo rapid coupling on treatment With proton sponge. The diastereoisomer of [C-p*RhCl{(C6F5)PhPC6H4SMe-2}]BF4, in which Cp* and C6F5 are trans, undergoes isomerization to 11a at a much slower rate than that of coupling. Cationic complexes of monodentate phosphines, in which there is rotation about the Rh-P bond, undergo coupling on addition of proton sponge, but at a much slower rate than for 1, 7, and 11a. The structures of [{eta(5),kappaP,kappaP-C5Me4CH2C6F4-2-P(C6F5)CH2CH2P(C6F5)(2)}RhCl]BF4, [{eta5,kappaP,kappaS-C5Me4CH2C6F4P(C6F5)C6H4SMe}RhCl]BF4, and [Cp*RhCl2{PEt2(C6F5)}] have been determined by single-crystal X-ray diffraction.