A comparison of the clusters [Os 3(μ-H)(μ-X)(CO) 10] where X is furyl, thienyl, pyrrolyl, or indolyl: monohapto versus dihapto and exo versus endo coordination

Abstract

The thienyl complexes [Os 3(μ-H)(μ-C 4H 2RS)(CO) 10] ( 1, R = H and 2, R = Me) were synthesised through the reactions of thiophene or 2-methylthiophene with [Os 3(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 μ,η 2-bonded, although the distance between an Os atom and the β-carbon is particularly long (Os(2)-C(2) 2.82(3) Å), longer than the corresponding distance in the previously reported furyl complex 3 (2.63(1) Å). 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 [Os 3(μ-H)(μ-C 4H 3NMe)(CO) 10] ( 5) but in this case the crystal structure shows that the pyrrolyl ring is perpendicular to the OS 3 ring and is μ-η 1-coordinated. Attempts to synthesise the directly analogous indol-2-yl complex, which we predict should be μ-η 2-coordinated, like the furyl and thienyl compounds, led instead to the indol-3-yl isomer [Os 3(μ-H)(μ-C 6H 4C 2HNMe)(CO) 10] ( 6), again with vertical μ,η 1-coordination, as shown by its crystal structure. A structural comparison of these compounds is presented.