Photochemical Alkyne Insertions into the Iron-Thiocarbonyl Bond of [Fe2(CS)(CO)3(Cp)2]

Internal alkynes (RC≡CR) react with [Fe2(CS)(CO)3(Cp)2] (1), under UV radiation, to give the complexes [Fe2μ-η1:η3-C(R)=C(R)C=S(μ-CO)(CO)(Cp)2] [R = Et, 2a; R = Ph, 2b; R = CO2Me, 2c], as a result of CO displacement and alkyne insertion into the metal-CS bond of 1. In addition, the reaction of 1 with EtC≡CEt affords the metallacycle species [Fe2μ- η2:η2-C(S)C(Et)=C(Et)C(O)(CO)2(Cp)2] (3) as secondary product. The molecular structures of 2a and 3 have been elucidated by X-ray diffraction studies. Compound 1 reacts with HC≡CCO2Me, affording the complex [Fe2μ- η1:η3-C(H)=C(CO2Me)C=S(μ-CO)(CO)(Cp)2] (2d) in modest yield. Complexes 2a,b undergo selective methylation at the sulfur atom, generating the cationic complexes [Fe2μ- η1:η3-C(R)=C(R)=C(SMe)(CO)(μ-CO)(Cp)2][CF3SO3] [R = Et, 4a; R = Ph, 4b]. The X-ray structure of 4a has also been determined. Finally, 4b undergoes nucleophilic addition of hydride and cyanide (from NaBH4 and NBun4CN, respectively) to form the vinylalkylidene complexes [Fe2μ- η1:η3-C(Ph)C(Ph)=C(X)(SMe)(CO)(μ-CO)(Cp)2] [X = H, 5; X = CN, 6].