Synthesis and reactions of the rhenium fulvene complexes [Re(η⁶-C₅Me₄CH₂)(CO) ₂(C₆F₄R)] (R = F or CF₃): Products derived from initial C-F activation

The UV irradiation of [Re(η⁵-C₅Me₅)(CO)₃] in the presence of C₆F₆ effected intermolecular C-F and intramolecular C-H activation generating [Re(η⁶-C₅Me₄CH₂)(CO) ₂(C₆F₅)] 1a in two isomeric forms. In the major isomer the CH₂ group lies trans to the C₆F₅ group both in solution and in the crystal. In the minor isomer the CH₂ lies cis to the C₆F₅ group. A similar reaction with C₆F₅CF₃ generates [Re(η⁶-C₅Me₄CH₂)(CO) ₂(C₆F₄CF₃)] 1b in four isomeric forms. In the major form the CF₃ group is in the 4 position and the CH₂ group lies trans to the C₆F₄CF₃ group. The other three isomers are formed by rotation of the η⁶-C₅Me₄CH₂ ligand as above, by placing the CF₃ at the 3 position, and by a combination of the two. Complex 1a reacted with PMe₃ to form the zwitterionic complex [Re(η⁵-C₅Me₄CH₂PMe ₃)(CO)₂(C₆F₅)] and with MeO^- to form the anion [Re(η⁵-C₅Me₄CH₂OMe)(CO) ₂(C₆F₅)]^-, isolable as the NEt₄⁺ salt. The reaction of 1a with HX (X = Cl or Br) generated cis-[Re(η⁵-C₅Me₅)(CO)₂(C ₆F₅)X] initially. More prolonged reaction led to the trans isomers. On reaction with HI, only the trans isomer was formed. Reaction of 1a with HBF₄ in Et₂O in the presence of MeCN led to formation of the salt [Re(η⁵-C₅Me₅)(CO)₂(C ₆F₅)(NCMe)]⁺[BF₄]^-. The halogens Cl₂, Br₂ and I₂ reacted to form (halogenomethyl)tetramethylcyclopentadienyl complexes trans-[Re(η⁵-C₅Me₄CH₂X)(CO) ₂(C₆F₅)X] (X = Cl, Br or I). The bromo complex has been characterized crystallographically.