Synthesis and structures of doubly-bridged dicyclopentadienyl dinuclear rhenium complexes, and their photochemical reactions with aromatic halides in benzene

Abstract

Reaction of the doubly-bridged biscyclopentadienes (C₅H₄(EMe₂))(C₅H₄(SiMe₂)) (E = Si(1a), or C(1b)) with Re₂(CO)₁₀ in refluxing mesitylene gave the corresponding dirhenium carbonyl complexes [(η⁵-C₅H₃)₂(EMe₂)(SiMe₂)][Re(CO)₃]₂ (trans-2a,b and cis-2a,b), and the desilylated products [(η⁵-C₅H₄)₂(EMe₂)][Re(CO)₃]₂ (3a,b). Photolysis of trans-2a,b with a series of aryl halides in benzene results in the formation of biphenyl, together with the corresponding rhenium dihalide complexes trans-[(η⁵-C₅H₃)₂(EMe₂)(SiMe₂)][Re(CO)₃][Re(CO)₂X₂] (X = Cl, Br, I) (4, 6, 8, or 10) and trans-[(η⁵-C₅H₃)₂(EMe₂)(SiMe₂)][Re(CO)₂X₂]₂ (5, 7, or 9). Additional experiments indicate that one phenyl ring in the resulting biphenyl comes from aryl halides and the other phenyl ring comes from the solvent benzene. However, photolysis of trans-2a with benzyl chloride and n-hexyl chloride in benzene afforded the corresponding bibenzyl and n-dodecane, as well as the rhenium dichlorides 8 and 9. In addition, complex trans-2a can also activate the C–F bond on C₆F₆ to form the pentafluorophenyl rhenium fluoride trans-[(η⁵-C₅H₃)₂(SiMe₂)₂][Re(CO)₃][Re(CO)₂(C₆F₅)F] (11). Molecular structures of cis-2a, cis-2b, trans-2b, 3b, 6, 7, 8, 11, and 12 determined by X-ray diffraction are also presented.