Iron(11) tris(2-pyridylthio)methanido (1) containing an Fe-C bond, obtained from the reaction of tris(2-pyridylthio)methane (HL1) and iron(II) triflate, reacts with protic acid to generate iron(II) bis(2-pyridylthio)carbene (la). The carbene complex is converted to an iron(II) complex (2) of the 1-[bis(2-pyridylthio)methyl]pyridine-2-thione ligand (L-3) upon treatment with a base. Complex 2 reversibly transforms to la in the presence of an acid. During the transformation of 1 to 2, a novel rearrangement of L-1 to L-3 takes place. The iron(II) complexes are reactive toward dioxygen to form the corresponding iron(III) complexes.