Intermediates and action effects in the activation of carbon-fluorine bonds by eta(5)-pentamethylcyclopentadienylrhodium halide complexes; crystal structure of [{eta(5)-C5Me3[CH2C6F4P(C6F5)CH2](2)-1,3}RhBr](+)center dot Br-

The reaction between [(eta(5)-C5Me5)RhBr(mu-Br)](2) and the diphosphine, (C 6F5)(2)PCH2CH2P(C6F5)(2) (dfppe), in benzene proceeded via the intermediate cation [(eta(5)-C5Me5)RhBr(dfppe)](+), which underwent C-F and C-H bond ac tivation and C-C bond formation to give sequentially [{eta(5)-C5Me4CH2C6F4P (C6F5)CH2CH2P(C6F5)(2)}RhBr](+) and then [{eta(5)-C5Me3[CH2C6F4P(C6F5)CH2]( 2)-1,3}RhBr](+), as evidenced by mass spectrometry and NMR spectroscopy. Th e bromide salt of the final product (4c) has been structurally characterize d by X-ray diffraction. Compound 4c crystallizes in the triclinic space gro up P (1) over bar with a = 10.616(1), b = 13.904(2), c = 14.911(1) Angstrom , alpha = 66.86(1), beta = 86.38(1), gamma = 84.72(1)degrees and Z = 2. Ref inement gave final R1 and wR2 [I = 2 sigma(I)] values of 0.0581 and 0.1641, respectively, for 6837 unique reflections. In contrast to the BF4- salt, t he Cl- and BPh4- salts of cation [(eta(5)-C5Me5)RhCl(dfppe)](+) undergo rea ction upon thermolysis in benzene the cation [(eta(5)-C5Me3[CH2C6F4P(C6F5)C H2](2)-1,3)RhCl](+). (C) 1999 Elsevier Science S.A. All rights reserved.