The reactions of pyridinyl thioesters with triiron dodecacarbonyl: their novel diiron carbonyl complexes and mechanistic investigations

Abstract

Reaction of Fe₃(CO)₁₂ with pyridinyl thioester ligand PyCH₂SCOCH₃ (L₁, Py = pyridin-2-yl) produced complex, [Fe₂(κ-COCH₃)(μ-SCH₂Py)(CO)₅] (1) (PyCH₂S = pyridin-2-ylmethanethiolate). When complex 1 reacted with PPh₃, a monosubstituted complex, [Fe₂(κ-COCH₃)(μ-SCH₂Py)(CO)₄PPh₃] (2), was derived. Reaction of the same precursor with analogous thioester ligand PyCH₂SCOPy (L₂) generated three novel diiron complexes, [Fe₂(κ-Py)(μ-SCH₂Py)(CO)₅] (3), [Fe₂(κ-Py)′(μ-SCH₂Py)(CO)₅] (4), and [Fe₂(κ-Py)(μ-SCH₂Py)(CO)₆] (5). Complexes 3 and 4 are structural isomers. Complex 5 could be converted into complex 4 but the conversion from complex 5 to the isomer 3 was not observed. All the five complexes were fully characterised using FTIR, NMR, and other techniques. Their structures were determined using X-ray single crystal diffraction analysis. The oxidative formation of complexes 1, 3, 4, and 5 involved C–S and/or C–C bonds cleavages. To probe possible mechanisms for these cleavages, DFT calculations were performed. From the calculations, viable reaction pathways leading to the formation of all the isolated products were delineated. The results of the theoretic calculations also allowed rationalisation of the experimental observations.