Molecular rearrangements of diynes coordinated to triosmium carbonyl clusters: the synthesis and structural characterisation of [Os3(μ-H)(CO)10{μ3-η1:η3:η1-Ph(C)C9H6)}], [Os3(μ-H)(CO)9{μ3-η1:η3:η1-Ph(C)C9H6)}] and [Os3(μ-H)(CO)8(MeCN){μ3-η1:η3:η1-Ph(C)C9H

The reaction between [Os3H2(CO)10] and 1,4-diphenylbuta-1,3-diyne yields two isomers of the triosmium cluster [Os3(μ-H)(CO)10{μ3-η1:η3:η1-Ph(C)C9H6)}] 1, 2, the structures of which involve an ‘open’ metal triangle and exhibit an unusual pseudo-allylic interaction involving a fused six- and five-membered ring system obtained from a ring-closure reaction of the diyne. Thermal decarbonylation of 1 and 2 produces [Os3(μ-H)(CO)9{μ3-η1:η3:η1-Ph(C)C9H6)}] (3) which has a ‘closed’ Os3 triangular core and the same formal μ3-η1:η3:η1-allylic coordination mode. The reaction of 1 with trimethylamine-N-oxide in the presence of acetonitrile affords [Os3(μ-H)(CO)8(MeCN){μ3-η1:η3:η1-(Ph(C)C9H6)}] (4), an acetonitrile-substituted derivative of 3. The structures of clusters 1–4 have been established by X-ray crystallography, and all the new clusters have been characterised spectroscopically.