Low‐Spin Pseudotetrahedral Iron(I) Sites in Fe 2 (μ‐S) Complexes

Fe I centers in iron–sulfide complexes have little precedent in synthetic chemistry despite a growing interest in the possible role of unusually low valent iron in metalloenzymes that feature iron–sulfur clusters. A series of three diiron [(L 3 Fe) 2 (μ‐S)] complexes that were isolated and characterized in the low‐valent oxidation states Fe II SFe II , Fe II SFe I , and Fe I SFe I is described. This family of iron sulfides constitutes a unique redox series comprising three nearly isostructural but electronically distinct Fe 2 (μ‐S) species. Combined structural, magnetic, and spectroscopic studies provided strong evidence that the pseudotetrahedral iron centers undergo a transition to low‐spin S =1/2 states upon reduction from Fe II to Fe I . The possibility of accessing low‐spin, pseudotetrahedral Fe I sites compatible with S 2− as a ligand was previously unknown.