Perfluorobenzyl Complexes of Cobalt and Rhodium. Unusual Coupling between Pentafluorophenyl and Pentamethylcyclopentadienyl Rings

Abstract

Oxidative addition of perfluorobenzyl iodide to [M(η5-C5R5)(CO)2] (M = Co, R = H, Me; M = Rh, R = Me) in benzene affords the perfluorobenzyl complexes [M(η5-C5R5)(CF2C6F5)I(CO)] (M = Co, R = H (1a), Me (2a); M = Rh, R = Me (2b)). Further reaction of 1a or 2a with PMe3 in benzene results in a substitution reaction to give complexes [Co(η5-C5R5)(CF2C6F5)I(PMe3)] (R = H (3a), Me (4a)) . While the reaction of (pentamethylcyclopentadienyl)cobalt complex 2a with PMe3 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 PMe2Ph in THF affords the analogous ring-coupled complex 9b, while reaction of the cyclopentadienyl analogue 1a with PMe2Ph affords the simple substitution product 5a. In contrast to the reactions of the (pentamethylcyclopentadienyl)cobalt complexes, reaction of the rhodium analogue 2b with PMe3 or PMe2Ph result in a simple substitution to give [Rh(η5-C5Me5)(CF2C6F5)I(L)] (L = PMe3 (5a) PMe2Ph (5b)). Attempts to purify complexes 9 result in facile hydrolysis of the CF2 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.