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

Abstract

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-C₅Me₄CH₂PMe₃)(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(C₆F₅)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(C₆F₅)(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.