A cationic rhenocene-acetonitrile adduct [Cp 2 Re(NCMe)](BF 4 ) (2) reacted with an excess of benzene and thiophene under UV irradiation to give the C-H bond activation products [Cp 2 Re(H)Ph](BF 4 ) (6) and [Cp 2 Re(H)(2-C 4 H 3 S)](BF 4 ) ( 7) in high yields. Deprotonation of 6 proceeded by treatment with DBU to give phenylrhenocene Cp 2 RePh (8), while protonation of 8 with HBF 4 regenerated 6.

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Abstract. A cationic rhenocene-acetonitrile adduct [Cp 2 Re(NCMe)](BF 4 )(1) reacted with an excess of benzene, thiophene, 2-methylthiophene, and pyrrole under UV irradiation to afford the C−H bond activation products [Cp 2 Re(H)R]BF 4 (R = phenyl, 2-thienyl, 2-(5-methylthienyl), 2-pyrrolyl) in high yields. In cases of thiophene derivatives and pyrrole, α-C−H bonds are selectively activated. A plausible mechanism involves the photodissociation of acetonitrile from 1 to generate a coordinatively unsaturated rhenocene cation [Cp 2 Re] + . When 2,5-dimethylthiophene and dibenzothiophene, having no α-C−H bonds, were used as substrates, products of the activation of other C−H bonds were formed first, but they isomerized to thermodynamically more stable η 1 -S-coordinated complexes in refluxing acetone. On the other hand, irradiation of the η 1 -S-coordinated complexes reproduced the original C−H bond activation products.