Reactivity of a (-Oxo)(-hydroxo)diiron(III) Diamond Core with Water,
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- 作者：Sonia Taktak ; Sergey V. Kryatov ; and Elena V. Rybak-Akimova
- 刊名：Inorganic Chemistry
- 出版年：2004
- 出版时间：November 1, 2004
- 年：2004
- 卷：43
- 期：22
- 页码：7196 - 7209
- 全文大小：257K
- 年卷期：v.43,no.22(November 1, 2004)
- ISSN：1520-510X
文摘
A series of iron(III) complexes of the tetradentate ligand BPMEN (N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine) were prepared and structurally characterized. Complex [Fe2(
-O)(-OH)(BPMEN)2](ClO4)3 (1) containsa (-oxo)(-hydroxo)diiron(III) diamond core. Complex [Fe(BPMEN)(urea)(OEt)](ClO4)2 (2) is a rare example of amononuclear non-heme iron(III) alkoxide complex. Complexes [Fe2(-O)(-OC(NH2)NH)(BPMEN)2](ClO4)3 (3) and[Fe2(-O)(-OC(NHMe)NH)(BPMEN)2](ClO4)3 (4) feature N,O-bridging deprotonated urea ligands. The kinetics andequilibrium of the reactions of 1 with ligands L (L = water, urea, 1-methylurea, 1,1-dimethylurea, 1,3-dimethylurea,1,1,3,3-tetramethylurea, and acetamide) in acetonitrile solutions were studied by stopped-flow UV-vis spectrophotometry, NMR, and mass spectrometry. All these ligands react with 1 in a rapid equilibrium, opening the four-membered FeIII(-O)(-OH)FeIII core and forming intermediates with a (HO)FeIII(-O)FeIII(L) core. The entropy andenthalpy for urea binding through oxygen are 
H
= -25 kJ mol-1 and S = -53.4 J mol-1 K-1 with anequilibrium constant of K1 = 37 L mol-1 at 25 C. Addition of methyl groups on one of the urea nitrogen did notaffect this reaction, but the addition of methyl groups on both nitrogens considerably decreased the value of K1.An opening of the hydroxo bridge in the diamond core complex [Fe2(-O)(-OH)(BPMEN)2] is a rapid associativeprocess, with activation enthalpy of about 60 kJ mol-1 and activation entropies ranging from -25 to -43 J mol-1K-1. For the incoming ligands with the -CONH2 functionality (urea, 1-methylurea, 1,1-dimethylurea, and acetamide),a second, slow step occurs, leading to the formation of stable N,O-coordinated amidate diiron(III) species such as3 and 4. The rate of this ring-closure reaction is controlled by the steric bulk of the incoming ligand and by theacidity of the amide group.
-O)(-OH)(BPMEN)2](ClO4)3 (1) containsa (-oxo)(-hydroxo)diiron(III) diamond core. Complex [Fe(BPMEN)(urea)(OEt)](ClO4)2 (2) is a rare example of amononuclear non-heme iron(III) alkoxide complex. Complexes [Fe2(-O)(-OC(NH2)NH)(BPMEN)2](ClO4)3 (3) and[Fe2(-O)(-OC(NHMe)NH)(BPMEN)2](ClO4)3 (4) feature N,O-bridging deprotonated urea ligands. The kinetics andequilibrium of the reactions of 1 with ligands L (L = water, urea, 1-methylurea, 1,1-dimethylurea, 1,3-dimethylurea,1,1,3,3-tetramethylurea, and acetamide) in acetonitrile solutions were studied by stopped-flow UV-vis spectrophotometry, NMR, and mass spectrometry. All these ligands react with 1 in a rapid equilibrium, opening the four-membered FeIII(-O)(-OH)FeIII core and forming intermediates with a (HO)FeIII(-O)FeIII(L) core. The entropy andenthalpy for urea binding through oxygen are H = -25 kJ mol-1 and S = -53.4 J mol-1 K-1 with anequilibrium constant of K1 = 37 L mol-1 at 25 C. Addition of methyl groups on one of the urea nitrogen did notaffect this reaction, but the addition of methyl groups on both nitrogens considerably decreased the value of K1.An opening of the hydroxo bridge in the diamond core complex [Fe2(-O)(-OH)(BPMEN)2] is a rapid associativeprocess, with activation enthalpy of about 60 kJ mol-1 and activation entropies ranging from -25 to -43 J mol-1K-1. For the incoming ligands with the -CONH2 functionality (urea, 1-methylurea, 1,1-dimethylurea, and acetamide),a second, slow step occurs, leading to the formation of stable N,O-coordinated amidate diiron(III) species such as3 and 4. The rate of this ring-closure reaction is controlled by the steric bulk of the incoming ligand and by theacidity of the amide group.