Oxidative addition of perfluorobenzyl iodide to [M(η 5 -C 5 R 5 )(CO) 2 ] (M = Co, R = H, Me; M = Rh, R = Me) in benzene affords the perfluorobenzyl complexes [M(η 5 -C 5 R 5 )(CF 2 C 6 F 5 )I(CO)] (M = Co, R = H ( 1a ), Me ( 2a ); M = Rh, R = Me ( 2b )). Further reaction of 1a or 2a with PMe 3 in benzene results in a substitution reaction to give complexes [Co(η 5 -C 5 R 5 )(CF 2 C 6 F 5 )I(PMe 3 )] (R = H ( 3a ), Me ( 4a )) . While the reaction of (pentamethylcyclopentadienyl)cobalt complex 2a with PMe 3 in benzene gives 4a, the analogous reaction in THF results in alkyl C−H activation and aryl C−F activation, with coupling of the pentamethylcyclopentadienyl ligand and the perfluorobenzyl ligand, to give 9a . Similarly, the reaction of 2a with PMe 2 Ph in THF affords the analogous ring-coupled complex 9b, while reaction of the cyclopentadienyl analogue 1a with PMe 2 Ph affords the simple substitution product 5a . In contrast to the reactions of the (pentamethylcyclopentadienyl)cobalt complexes, reaction of the rhodium analogue 2b with PMe 3 or PMe 2 Ph result in a simple substitution to give [Rh(η 5 -C 5 Me 5 )(CF 2 C 6 F 5 )I(L)] (L = PMe 3 ( 5a ) PMe 2 Ph ( 5b )). Attempts to purify complexes 9 result in facile hydrolysis of the CF 2 group to give acyl complexes 10 . A mechanism is proposed for this coupling reaction, and an analogue 13 of a proposed cationic intermediate has been isolated and shown to react with iodide to afford 10, via 9a . Heating of 2a results in a different coupling reaction to afford the organic cyclopentadiene 14 . The solid state structures of 3a, 5b, and 10b were determined by X-ray crystallography.
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Hughes et al. (1996) studied this question.