SYNTHESIS AND PROTONATION OF THE BRIDGING BENZO[B]THIOPHENE (BT) COMPLEXES [CP'(CO)2RE](ETA-2-ETA-1(S)-MU-2-BT)[RE(CO)2CP'']

The bimetallic complexes [CP'(CO)2Re](eta2:eta1(S)-mu2-BT)[Re(CO)2CP''], where Cp' and Cp'' are eta5-CrH5(Cp) or -C5Me5(Cp*) and BT = benzo[b]thiophene, are prepared by reaction of the monometallic complex CP'(CO)2Re(BT) with a catalytic amount of CF3SO3H or by the reaction Of CP'(CO)2Re(THF) with BT. An X-ray structural study of [CP(CO)2Re]2(eta2:eta1(S)-mu2-BT) shows that one Re is eta2-coordinated to the 2,3-olefin of the BT and the other is eta1(S)-coordinated to the sulfur. Infrared and NMR data of these bimetallic complexes suggest that this dual metal coordination to BT enhances the binding abilities of both the sulfur and C2-C3 olefin groups to the Re atoms. When these bimetallic complexes are reacted with 1 equiv of CF3SO3H, the complexes protonate exclusively at the Re atom that is eta1(S) bonded to the BT. The protonated complexes are fluxional, and this fluxionality can be explained in terms of cis-trans isomerization at the protonated metal center. This same type of fluxionality is observed in the protonated complex [CP(CO)2Re(H)(PPh3)]O3SCF3.