Synthesis, characterization, and reactivity of sulfided hexanuclear molybdenum cluster compounds

Spink, Deborah
Major Professor
Robert E. McCarley
Committee Member
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Hexanuclear molybdenum clusters with mixed chloride and sulfide bridging ligands were prepared by reacting [alpha]-MoCl[subscript]2 with sodium hydrosulfide in the presence of sodium butoxide. The resulting species, Mo[subscript]6Cl[subscript] (8-x)S[subscript] x·npy (x ≅ 3.6, n ≅ 4, py = pyridine), was pyrophoric and insoluble. By reaction with triethylphosphine in refluxing toluene, the soluble triethylphosphine derivatives was obtained. The Mo[subscript]6Cl[subscript] (8-x)S[subscript] x·6PEt[subscript]3 (4 ≤ x ≤ 8), mixture was separated by normal chromatographic methods using a combination of Celex-N-1 and basic alumina columns. The mixed sulfide chloride cluster species Mo[subscript]6S[subscript]4Cl[subscript]4·6OPEt[subscript]3 and Mo[subscript]6S[subscript]~ 5Cl[subscript]~ 3·6PEt[subscript]3, and Mo[subscript]6S[subscript]8·6PEt[subscript]3 were isolated and characterized. Infrared spectroscopy was used as the primary characterization tool. Elemental analyses provided information on the extent of sulfide substitution for each fraction. Additionally, phosphorus-31 nuclear magnetic resonance, electron paramagnetic resonance, and UV/visible spectra were obtained for each fraction;The completely sulfided cluster, Mo[subscript]6S[subscript]8·6PEt[subscript]3, was prepared similarly and used in various experiments as a possible precursor to Chevrel phase materials of the type Mo[subscript]6S[subscript]8 or M[subscript] nMo[subscript]6S[subscript]8. With the goal of removing all of the triethylphosphine ligands, Mo[subscript]6S[subscript]8·6PEt[subscript]3 was reacted with the transition metal carbonyls molybdenum hexacarbonyl and dicobalt octacarbonyl. The insoluble products were characterized by infrared spectroscopy which showed that coordinated triethylphosphine remained. These materials were amorphous to x-rays;Reaction of the molecular sulfide cluster with copper(I) chloride in toluene gave a completely insoluble product. The infrared spectra did show however, absorptions in the regions expected for coordinated triethylphosphine. The reaction of Mo[subscript]6S[subscript]8·6PEt[subscript]3 with propylene sulfide gave a product whose infrared spectra showed only very weak peaks associated with coordinated triethylphosphine. The elemental analysis of this product fit the formula Mo[subscript]6S[subscript]8·5SPEt[subscript]3. The Mo[subscript]6S[subscript]8·6PEt[subscript]3 cluster was recovered by reacting this material with triethylphosphine with liberation of SPEt[subscript]3;Finally, reactivity of the outer ligands of the Mo[subscript]6S[subscript]8·npy and Mo[subscript]6S[subscript]8·(6-x)PrNH[subscript] x clusters were investigated. Pyridine is not readily replaced by the thioethers thiophene, tetrahydrothiophene, or ethyl sulfide. Crystalline Mo[subscript]6S[subscript]8·6THT was recovered from the reaction of the n-propylamine derivative with THT. A crystal structure determination was done: cubic space group I a3 with a = 20.313 (3) A, V = 8381.3 A[superscript]3, Z = 8, R = 0.060, R[subscript] w = 0.046.