Synthesis, structure, and properties of a mixed-valent triiron complex of tetramethyl reductic acid, an ascorbic acid analogue, and its relationship to a functional non-heme iron oxidation catalyst system.
The purple triiron(II,III,III) complex, [Fe(3)Cl(2)(TMRASQ)(4)(HTMRA)(2)] x C(5)H(12) (1 x C(5)H(12)), where H(2)TMRA is a tetramethyl reductic acid, 4,4,5,5-tetramethyl-2,3-dihydroxy-2-cyclopenten-1-one, and HTMRASQ is the semiquinone form of this ligand, was prepared from (Et(4)N)(2)[Fe(2)OCl(6)] and H(2)TMRA and characterized by X-ray crystallography, Mössbauer spectroscopy, and redox titrations. The physical properties of the complex in solution are consistent with its mixed-valent character, as delineated by a solid-state structure analysis. Assignments of the iron and ligand oxidation states in the crystal were made on the basis of a valence bond sum analysis and the internal ligand geometry. As the first well-characterized iron complex of an ascorbic acid H(2)AA analogue, 1 provides insight into the possible coordination geometry of the family of complexes containing H(2)AA and its analogues. In the presence of air and H(2)TMRA, 1 is able to catalyze the oxidation of cyclohexane to cyclohexanol with remarkable selectivity, but the nature of the true catalyst remains unknown.
Kim
YooJin
Y
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Feng
Xudong
X
Lippard
Stephen J
SJ
D001205:Ascorbic Acid / Q000737:chemistry*; D002384:Catalysis; D002621:Chemistry / Q000379:methods*; D018360:Crystallography, X-Ray; D003510:Cyclohexanes / Q000737:chemistry; D003517:Cyclopentanes / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared; D015204:Spectroscopy, Mossbauer; D013057:Spectrum Analysis / Q000379:methods*
D003510:Cyclohexanes; D003517:Cyclopentanes; D008024:Ligands; D012997:Solvents; C064295:reductic acid; C506365:Cyclohexane; D007501:Iron; D001205:Ascorbic Acid; D010100:Oxygen