Triosmium clusters bridging ligands

This section is dedicated to a description of the chemistries of trinithenium and triosmium clusters that do not contain hydrocarbon ligands. This section should be viewed as an addition to the chemistry described in sections 32.5 and 33 of COMC (1982) and section 12 of COMC (1995) as most of the main themes have been developed in the previous two decades. Overall, the interest in the cluster chemistry of ruthenium and osmium during the period 1994-2004 has tended to focus mainly on higher nuclearity and mixed metal clusters in order to enhance the developments in catalysis and bridge the gap between molecular clusters and nanoparricles. However, triruthenium and triosmium clusters continue to play a pivotal role in the chemistry of ruthenium and osmium. Both classes of clusters can be, and are, used extensively as precursors for the synthesis of higher nuclearity clusters as well as the formation of mono- and bimetallic complexes. No up-to-date review of the chemistry of either Ru3(CO)i2 or Os3(CO)i2 and their compounds is available, but several annual reviews of the chemistry of mthenium and osmium, which include the chemistry of the trinuclear clusters, are available. ... 

Os3(CO)io(NCMe)2 reacts with phenylthiourea and jV,7V -diphenylthiourea to yield the thioureato-triosmium cluster complexes Os3(jU-H)(CO)io //-SG=NH(NH2) and Os3(jU-H)(CO)io /x-SC=NPh(NPhH) in which the thioureate moiety bridges two osmium atoms via the sulfur atom. Photolysis of the complexes results in loss of CO and secondary coordination of a nitrogen atom of the thioureate ligand. ... 

Morrison, E.D., GeofFroy, G.L. and Rheingold, A.L. (1985) Halide-promoted insertion of CO into bridging-methylene ligands in triosmium clusters. Journal of the American Chemical Society, 107, 254—255. 

Similarly, thermolysis of the triosmium NHC cluster Os3(ImMe2)(CO)n affords the edge-bridged (24, M — Os) and derivatives (21, M = Os), resulting from sequential oxidative addition of one and two C-H bonds, respectively the ruthenium analogue 21 is prepared from a similar reaction, which affords as minor products the pentanuclear clusters 25 and 26 containing p4-q2-CO ligands.29... 

The rhodium complex [Rh(acac) (C2Hi )2] reacts with the unsaturated triosmium compound to give the 60-electron cluster species [Rh0s3(y-H)2(y-acac)(CO)10J (A7) in which the acac ligand acts as a five-electron donor, one oxygen atom bridging an Os — Rh separation of 3.292(2) so that the four metal atoms adopt a butterfly configuration. 

In contrast, when thiophenes react with triosmium carbonyl clusters it is C-H bond activation that occurs in preference to C-S bond cleavage. The direct reaction of [Os3(CO)i2], or the -acetonitrile complex [Os3(CO)io(NCMe)2], with thio-phene results in the oxidative addition of a C-H bond to give the exo- and endo isomers of the n, -thienyl hydrido cluster [Os3(//-H)(/z-C4H3S)(CO)io] (21a, 22a) (Scheme 7). These isomers are in rapid equilibrium at room temperature. The complex [Os3(/i-H)2(/X3-C4H2S)(CO)9] (23a) also results from his reaction, presumably by additional thermal C-H bond activation and decarbonylation of the thienyl complex. This cluster contains a triply bridging cyclic alkyne ligand related to /i3-benzyne. " ... 

---