Photochemical Reactions of [(η 5 ‐C 5 R 5 )Re(CO) 3 ] (R = Me or H) with Aryl Halides in Benzene: Stoichiometric Formation of Biphenyl

Photolysis of [Cp*Re(CO) 3 ] (Cp* = η 5 ‐C 5 Me 5 ) with bromobenzene or chlorobenzene in benzene results in biphenyl and the corresponding rhenium hydride halide complex trans ‐[Cp*Re(CO) 2 H(X)], which further converts into the dihalide complexes cis / trans ‐[Cp*Re(CO) 2 X 2 ] (X = Br, Cl). Additional experiments, including isotopic labeling experiments, indicate that one phenyl ring in biphenyl comes from the aryl halide and the other one comes from solvent benzene. Photolysis of [CpRe(CO) 3 ] (Cp = η 5 ‐C 5 H 5 ) with aryl halide in benzene similarly generates biphenyl, the corresponding rhenium hydride halide complex. Furthermore, the reaction also affords small amounts of rhenium dihydride complex [CpRe(CO) 2 H 2 ]. Plausible mechanisms for the formation of the different types of products are proposed that involve intermolecular C–X and C–H activation. Molecular structures of trans ‐[Cp*Re(CO) 2 (Br)(Cl)] ( trans ‐ 6 ) and trans ‐[CpRe(CO) 2 (Br)(Cl)] ( trans ‐ 12 ) determined by X‐ray diffraction are also presented.