A COMPARISON OF THE CLUSTERS [OS3(MU-H)(MU-X)(CO)10] WHERE X IS FURYL, THIENYL, PYRROLYL, OR INDOLYL - MONOHAPTO VERSUS DIHAPTO AND EXO VERSUS ENDO COORDINATION

The thienyl complexes [Os3(mu-H)(mu-C4H2RS)(CO)10] (1, R = H and 2, R = Me) were synthesised through the reactions of thiophene or 2-methylthiophene with [Os3(CO)10(MeCN)2], which lead to C-H bond activation adjacent to the sulphur atom. The crystal structure when X = Me shows that the thienyl ligand is mu, eta-2-bonded, although the distance between an Os atom and the beta-carbon is particularly long (Os(2)-C(2) 2.82(3) angstrom, longer than the corresponding distance in the previously reported furyl complex 3 (2.63(1) angstrom). The presence and interconversion of exo and endo isomers of these complexes in solution are described. The interconversion mechanism is believed to involve a transient heteroatom-bonded intermediate. N-Methylpyrrole similarly gives the stoichiometrically equivalent but structurally different cluster [Os3(mu-H)(mu-C4H3NMe)(CO)10] (5) but in this case the crystal structure shows that the pyrrolyl ring is perpendicular to the Os3 ring and is mu,eta-1-coordinated. Attempts to synthesise the directly analogous indol-2-yl complex, which we predict should be mu-eta-2-coordianted, like the furyl and thienyl compounds, led instead to the indol-3-yl isomer [Os3(mu-H)(mu-C6H4C2HNMe)(CO)10] (6), again with vertical mu,eta-1-coordiantion, as shown by its crystal structure. A structural comparison of these compounds is presented.