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

Abstract

The reaction of [Os3Rh(μ-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 [Os 5Rh2(μ-CO){η6-C6H 4(CH3)2}(CO)16]1, [Os 5Rh2(μ-CO)(η6-C6H 5Cl)(CO)16] 2 and [Os5Rh2(μ-CO) (η6-C5H6)(CO)16] 3. The treatment of [Os3Rh(μ-H)3(CO)12] in refluxing toluene with an excess amount of 4-vinylphenol afforded a new complex, [Os4Rh(μ-H)(η6-C6H5CH 3)(CO)12] 4, which was isolated as a brown complex in 20% yield together with two known compounds, [Os5́Rh2(η 6-C6H5CH3)(μ-CO)(CO) 16] in 10% yield and [Os3Rh4(μ3- η11η1·η1·η 1-C6H5CH3) (CO)13] in 5% yield. Complexes 1-4 were fully characterized by IR, 1H 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(η6- C6H5CH3)(μ-CO)(CO)16] with [Os3(μ-H)2(CO)10] in chloroform under reflux resulted in two hydrogen-rich compounds: [Os7Rh3(μ-H) 11(CO)23] 5 and [Os5Rh3Cl(μ-H) 8(CO)18] 6, both in moderate yields. The reaction of [Os5Rh2(η6-C6H 5CH3)(μ-CO)(CO)16] with hydrogen in refluxing chloroform yielded a new cluster compound, [Os5Rh(μ-H) 5(CO)18] 7, in 20% yield, together with a known osmium-rhodium cluster, [Os6Rh(μ-H)7(μ-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 [Os7Rh 3(μ-H)11(CO)23] 5 and [Os5Rh 3Cl(μ-H)8 (CO)18] 6. Both the compounds proved to be able to exchange the H atom with D in the presence of D 2SO4, and the absence of the hydride signal in the 1H NMR spectrum is consistent with this. Therefore, clusters 5 and 6 may serve as appropriate new hydrogen storage models. © The Royal Society of Chemistry 2005.