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

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 [(η(5)-C5H3)2(EMe2)(SiMe2)][Re(CO)3]2 (trans-2a,b and cis-2a,b), and the desilylated products [(η(5)-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-[(η(5)-C5H3)2(EMe2)(SiMe2)][Re(CO)3][Re(CO)2X2] (X = Cl, Br, I) (4, 6, 8, or 10) and trans-[(η(5)-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-[(η(5)-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.