Synthesis and Reactivity of the Imido-Bridged Metallothiocarboranes CpCo(S2C2B10H10)(NSO2R)

The reactions of the 16-electron half-sandwich complex CpCo­(S2C2B10H10) (1) (Cp: cyclopentadienyl) with sulfonyl azides (p-toluenesulfonyl azide, TsN3; methanesulfonyl azide, MsN3) in refluxing dichloromethane or at ambient temperature lead to imido-bridged adducts CpCo­(S2C2B10H10) (NSO2R) (2a, R = 4-MePh; 2b, R = Me) which can convert to the tetraazadiene cobalt complexes CpCoN4(SO2R)2 (3a, R = 4-MePh; 3b, R = Me) in the presence of excess azide if heated. The reactions of 1 with acyl azides (methyl azidoformate and benzoyl azide) lead to CpCo­(S2C2B10H10)­(CONR) (4a, R = OMe; 4b, R = Ph) with a newly-generated five-membered metallacyclic ring Co–S–N–C–O. Complexes 2a and 2b show further reactivity toward alkynes to give rise to the insertion products CpCo­(S2C2B10H10)­(R1CCR2) (NSO2R) (R1 = COOMe, R2 = H, R = 4-MePh, 5a, R = Me, 5b; R1 = R2 = COOMe, R = 4-MePh, 6a, R = Me, 6b; R1 = COOMe, R2 = Ph, R = 4-MePh, 8a, R = Me, 8b) formed by alkyne addition to a Co–S bond to generate a Co–C–C–S four-membered ring and CpCo­(S2C2B10H10)­(R1CCR2NSO2R) (R1 = H, R2 = Ph, R = 4-MePh, 7a, R = Me, 7b; R1 = COOMe, R2 = Ph, R = 4-MePh, 9a, R = Me, 9b) formed by alkyne insertion into a Co–N bond to generate a Co–C–C–N–S five-membered ring. In the case of PhCCCO2Me, the products with insertion into both Co–S and Co–N bonds are isolated. Interestingly, if tert-butylacetylene is used, CpCo­(S2C2B10H10)­(R1R2CCNSO2R) (R1 = tBu, R2 = H, R = 4-MePh, 10a, R = Me, 10b) are generated by insertion of terminal carbon into a Co–N bond to form four-membered ring Co–C–N–S. The insertion pathways of these reactions have been discussed on the basis of DFT calculations. All the new complexes were fully characterized, and X-ray structural analyses were performed for 2a, 3a, 3b, 4a, 4b, 5a, 6a, 7a, 7b, 8a, 9a, 9b, and 10b.