Synthesis and structural characterization of a series of high-hydride content osmium-rhodium carbonyl complexes by the hydrogenation of arene-coordinated clusters

The reaction of [Os3Rh(mu-H)(3)(CO)(12)] with an excess amount of 4-vinylphenol (as hydride acceptor) in refluxing m-xylene, chlorobenzene or benzene yielded the three new clusters [Os5Rh2(mu-CO){eta(6)-C6H4(CH3)(2)}(CO)(16)] 1, [Os5Rh2(mu-CO)(eta(6)-C6H5Cl)(CO)(16)] 2 and [Os5Rh2(mu-CO)(eta(6)-C6H6)(CO)(16)] 3. The treatment of [Os3Rh(mu-H)(3)(CO)(12)] in refluxing toluene with an excess amount of 4-vinylphenol afforded a new complex, [Os4Rh(mu-H)(eta(6)-C6H5CH3)(CO)(12)] 4, which was isolated as a brown complex in 20% yield together with two known compounds, [Os5Rh2(eta(6)-C6H5CH3)(mu-CO)(CO)(16)] in 10% yield and [Os3Rh4(mu(3)-eta(1): eta(1): eta(1)-C6H5CH3)(CO)(13)] in 5% yield. Complexes 1-4 were fully characterized by IR, H-1 NMR spectroscopy, mass spectroscopy, elemental analysis and X-ray crystallography. The molecular structures of compounds 1-3 are isomorphous, and only differ in the arene-derivatives that attach to the same metal core. Their metal cores can be viewed as a monocapped octahedral, in which an osmium atom caps one of the Os-Os-Os triangular faces of the Os4Rh2 metal framework. Complex 4 has a trigonal-bipyramidal metal core with a C6H5Me ligand that is terminally bound to the Rh atom that lies in the trigonal plane of the metal core. The hydrogenation of [Os5Rh2(eta(6)-C6H5CH3)(mu-CO)(CO)(16)] with [Os3(mu-H)(2)(CO)(10)] in chloroform under reflux resulted in two hydrogen-rich compounds: [Os7Rh3(mu-H)(11)(CO)(23)] 5 and [Os5Rh3Cl(mu-H)(8)(CO)(18)] 6, both in moderate yields. The reaction of [Os5Rh2(eta(6)-C6H5CH3)(mu-CO)(CO)(6]) with hydrogen in refluxing chloroform yielded a new cluster compound, [Os5Rh(mu-H)(5)(CO)(18)] 7, in 20% yield, together with a known osmium-rhodium cluster, [Os6Rh(mu-H)7(mu-CO)(CO)(18)], as a major compound. Clusters 5, 6 and 7 have been fully characterized by both spectroscopic and crystallographic methods. Additionally, a deuterium-exchange experiment was performed on [Os7Rh3(mu-H)(11)(CO)(23)] 5 and [Os5Rh3Cl(mu-H)(8)(CO)(18)] 6. Both the compounds proved to be able to exchange the H atom with D in the presence of D2SO4, and the absence of the hydride signal in the H-1 NMR spectrum is consistent with this. Therefore, clusters 5 and 6 may serve as appropriate new hydrogen storage models.