THE CATALYTIC CYCLOOLIGOMERIZATION OF THIETANE BY TRIRHENIUM CLUSTER COMPLEXES - A NEW ROUTE TO POLYTHIAETHER MACROCYCLES

The trirhenium complex Re-3(CO)(10)[mu-SCH2CH2CH2](mu-H)(3) (1) reacts with dimethyl sulfide by a ring opening addition to the bridging thietane Ligand to yield the zwitterionic complex Res(CO)(10)[mu-SCH(2)CH(2)CH(2)SMe(2)]-(mu-H)(3) (2) in 48% yield that contains a sulfonium-substituted thiolate ligand bridging an edge of the cluster. The structure of 2 was established by a single-crystal X-ray diffraction analysis. The reaction of 1 with thietane was found to produce a ring-opening oligomerization of thietane to yield the new complexes Re-3(CO)(10)[mu-SCH2CH2-CH2S CH2CH2CH2SCH2CH2CH2SCH2CH2CH(2)](mu-H)(3) (3), Re-3(CO)(10)[mu-SCH2CH2CH2SCH2CH2CH2(SCH2CH2CH2)(2)-SCH2CH2CH2](mu-H)(3) (4), and Re-3(CO)(10)[mu-SCH2CH2CH2SCH2CH2CH2(SCH2CH2CH2)(4)SCH2CH2CH2](mu-H)(3) (5), depending on how much thietane reagent is used. Compounds 3, 4, and 5 were characterized fully as their PMe(2)Ph derivatives, 6, 7, and 8. Compound 6 was also characterized by a single crystal X-ray diffraction analysis. Compound 6 contains a bridging thiolato ligand [mu-SCH2CH2CH2SCH2CH2CH2SCH2CH2CH2SCH2CH2] that is terminated with the macrocyclic grouping 1,5,9-trithiacyclododecane (12S3), through the formation of a sulfonium center. The macrocycles 12S3, 1,5,9,13-tetrathiacyclohexadecane, (16S4), and 1,5,9,13,17,21-hexathiacyclotetracosane (24S6), were cleaved from the complexes 6, 7, and 8, respectively, by treatment with pyridine. The free macrocycles, 12S3 and 24S6, were obtained catalytically when 1, 3, or Re-3(CO)(12)(mu-H)(3) was allowed to react with thietane in the absence of solvent at reflux. 3,3,7,7,11,1 1,15,15,19,19,23,23-Dodecamethyl-1,5,9,13,17,21-hexathiacyclotetracosane (Me(12)-24S6) was obtained catalytically as the only organic product when 3,3-dimethylthietane was allowed to react with Re-3(CO)(10)[mu-SCH(2)CMe(2)CH(2)](mu(3)-H)(3) in the absence of solvent at its refluxing temperature. Crystal data for 2.0.5Me(2)C=O: space group P (1) over bar, a = 12.295(2) Angstrom, b = 12.341(2) Angstrom, c = 8.568(1) Angstrom, alpha = 101.76(1)degrees, beta = 91.37(2)degrees, gamma = 97.66(2)degrees, Z = 2, 2344 reflections, R = 0.040. Crystal data for 6: space group P2(1)/n, a = 8.637(2) Angstrom, b = 41.80(1) Angstrom, c = 11.418(2) Angstrom, beta = 111.79(2)degrees, Z = 4, 2836 reflections, R = 0.036.