Low-Spin Pseudotetrahedral Iron(I) Sites in Fe2(μ-S) Complexes

摘要

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 metallo-enzymes that feature iron-sulfur clusters. A series of three diiron [(L3Fe)2(μ-S)] complexes that were isolated and characterized in the low-valent oxidation states Fe~(II)—S—Fe~(II), Fe~(II)S— Fe~I, and Fe~IS—Fe~I is described. This family of iron sulfides constitutes a unique redox series comprising three nearly isostructural but electronically distinct Fe2(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.