OLEFIN VERSUS SULFUR COORDINATION OF BENZO[B]THIOPHENE (BT) IN CP(CO)(2)RE(ETA(2)-ETA(6)-MU(2)-BT)CR(CO)(3)

Reactions of Cr(CO)(3)(eta(6)-BT), in which the Cris pi-coordinated to the benzene ring of benzo [b] thiophene (BT), with Cp' (CO),Re(THF), where Cp' = eta(5)-C5H5 or eta(5)-C(5)Me(5), give the products Cp'(CO) (2)Re(eta(2):eta(6)-mu(2)-BT)Cr(CO)(3) in which the Cr remains coordin ated to the benzene rin g and Re is bound to the C(2)=C(3) double bond . An X-ray diffraction study of Cp(CO)(2)Re(eta(2):eta(6)-mu(2)-BT)Cr( CO)(3) (3) provides details of the geometry. This structure contrasts with that of the Cp'(CO),Re(BT) complexes that exist as mixtures of is omers in which the BT is coordinated to the Re through either the doub le bond (2,3-eta(2)) Or the sulfur (eta(1)(S)). Thus, the electron-wit hdrawing Cr(CO)(3) group in 3 stabilizes the 2,3-eta(2) mode of BT coo rdination to the Cp'(CO)(2)Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data f or 3: triclinic, space group P (1) over bar, a = 6.716(2), b = 11.651 (2), c = 11.956(2) Angstrom, alpha = 70.20(2),beta = 74.84(2), gamma = 89.90(2)degrees, Z= 2.