Investigation of Coordination Modes of Organosulfur Ligands to osmium and Rhodium Carbonyl Clusters- Possible Relevance to Hydrodesulfurization Reactions

Abstract: The coordination and fundamental transformations of organosulfur compounds to polynuclear metal complexes has been studied as models for possible surface species in industrial HDS processes. Reactions between [Os3(CO)11(NCMe)] and various thiols have been studied by UV-Vis, IR and NMR spectroscopy and all experimental findings indicate that the reactions proceed via a two-step consecutive process involving the intermediate [Os3(CO)11(RSH)], which contains an agostic Os-H-S interaction, and which leads to the formation of the final product [Os3(CO)10(m-H)(m-SR)]. Reaction of [Rh4(CO)12] with para-thiocresol leads to a quantitative conversion to the dimeric complex [Rh2(CO)4(m-SC6H4-p-Me)]. The reaction involves evolution of H2 which was detected by GC-MS. Reaction of [Os3(CO)11(NCMe)] with thioethers results in the formation of [Os3(CO)11(L)] (L= thioether). The reaction of [Os3(CO)10(NCMe)2] with thioethers is less predictable and monosubstituted as well as disubstituted clusters are observed. Thioethers with aryl substituents undergo oxidative addition of a C-H bond of an aryl ring when reacted with [Os3(CO)10(NCMe)2]. Reaction of [Os3(m-H)2(CO)10] with thioethers does not lead to discernable products except when carried out in the presence of trimethylamine N-oxide, which leads to clusters of the general formula [Os3(m-H)2(CO)9(L)] (L= thioether). Thermal treatment of [Os3(CO)12] with Ph2P(C4H3S) and Ph2P(C8H5S) at 110 °C results in the formation of the simple substitution products [Os3(CO)12-n{Ph2PR}n] (n=1-3, R= -C4H3S, -C8H5S). At elevated temperatures C-H activation as well as sulfur coordination is observed for Ph2P(C8H5S). Treatment of Ph2P(C4H3S) and Ph2P(C8H5S) with [Os3(m-H)2(CO)10] at room temperature leads to the expected clusters [HOs3(m-H)(CO)10{Ph2PR}] (R= -C4H3S, -C8H5S), but at higher temperatures further metallation as well as sulfur coordination is observed. Several of the products of the reactions with diphenyl-2-thienylphosphine and diphenyl-benzothienylphosphine showed fluxional behavior and the dynamic behaviors have been studied by variable temperature 1H and 31P{1H} NMR spectroscopy.