The cluster/surface analogy: the binding of norbornene on a triangulated array of metals

Reactions of [Os-3(CO)(10)(NCMe)(2)] 1 with norbornene (bicyclo[2.2.1]hept-2-ene, nbe) led to two isomeric triosmium clusters [Os-3(mu-H)(CO)(10)(mu-eta(1):eta(2)-C7H9)] 2 and 3 and also the dihydride species [Os-3(mu-H)(2)(CO)(9)(mu(3)-eta(1):eta(2):eta(1)-C7H8)] 4. The molecular structure of compound 4 established by single crystal X-ray analysis shows norbornene-metal interactions similar to the proposed adsorption mode of norbornene found on the Pt(111) surface. The two isomers 2 and 3 exhibit an intermediate bonding mode between the solely pi bound ligand and the di-sigma,pi bonding mode exhibited by cluster 4. These isomers differ in the orientation of the C7H8 moiety with respect to the triosmium triangle. Both 2 and 3 may exist in other isomeric forms which differ in the location of the hydride ligand. Compound 2 converts into 3 which on heating undergoes C-H bond cleavage to produce 4.