Photochemical reactions of [Re(η5-C5R5)(CO)3] (R = H or Me) with partially fluorinated benzenes: C–H and C–F activation

Abstract

UV Irradiation of [Re(η⁵-C₅R₅)(CO)₃] (R = Me or H) in the presence of C₆F₅H or 1,2,4,5-C₆F₄H₂ effected intramolecular C–H activation, generating the hydrido complexes trans-[Re(η⁵-C₅R₅)(CO)₂(Ar)_FH] [(Ar)_F = C₆F₅ or 2,3,5,6-C₆F₄H] as the principal photochemical products. The identities of the hydrido complexes were confirmed by independent thermal syntheses. The photoreaction of [Re(η⁵-C₅Me₅)(CO)₃] with C₆F₅H also generated the fulvene complex [Re(η⁶-C₅Me₄CH₂)(CO)₂(C₆F₅)] 2a and two bis(aryl) derivatives: cis-[Re(η⁵-C₅Me₅)(CO)₂(C₆F₅)₂] 3a and [Re(η⁵-C₅Me₅)(CO)₂(C₆F₅)(2,3,5,6-C₆F₄H)] 4a in low yield. Complex 2a results from an intramolecular C–H activation, while 3a and 4a derive from a C–H and a C–F activation of a second molecule of pentafluorobenzene, respectively. The origin of the minor products was elucidated by showing that UV irradiation of [Re(η⁵-C₅Me₅)(CO)₂(C₆F₅)H] in C₆F₅H produces 2a, 3a and 4a, while photolysis of 2a produces only 3a. The reaction of [Re(η⁵-C₅Me₅)(CO)₃] with 1,2,4,5-C₆F₄H₂ gave analogues 2b and 4b as minor products. The photoreaction of [Re(η⁵-C₅H₅)(CO)₃] in C₆F₅H or 1,2,4,5-C₆F₄H₂ generated bis(aryl) compounds and the unusual binuclear complexes [Re₂(η⁵-C₅H₅)(µ-η¹∶η⁵-C₅H₄)(CO)₄(Ar)_F] as the minor products. The binuclear complex with (Ar)_F = 2,3,5,6-C₆F₄H has been characterized by X-ray crystallography. The Re–Re bond [3.0258(7) Å] is close to collinear with the Re–C (aryl) bond. One {Re(CO)₂} unit is twisted by about 73.0° with respect to the other.