Aminopyridine Iron Catecholate Complexes as Models for Intradiol Catechol Dioxygenases. Synthesis, Structure, Reactivity, and Spectroscopic Studies
详细信息 查看全文
- 作者：Pierre Mialane ; Luba Tchertanov ; Fré ; dé ; ric Banse ; Joelle Sainton ; and Jean-Jacques Girerd
- 刊名：Inorganic Chemistry
- 出版年：2000
- 出版时间：June 12, 2000
- 年：2000
- 卷：39
- 期：12
- 页码：2440 - 2444
- 全文大小：108K
- 年卷期：v.39,no.12(June 12, 2000)
- ISSN：1520-510X
文摘
Four new Fe(III) catecholate complexes, [(bispicMe2en)FeIII(DBC)]+, [(bispicCl2Me2en)FeIII(DBC)]+, [(trispicMeen)FeIII(DBC)]+, and [(BQPA)FeIII(DBC)]+, which all contain aminopyridine ligands, were synthesized. Thestructure of [(bispicMe2en)FeIII(DBC)]+ was determined by X-ray diffraction. It crystallizes in the triclinic spacegroup P
nals/inocaj/39/i12/eqn/ic981236ve10001.gif"> with a = 10.666(3) Å, b = 13.467(5) Å, c = 17.685(2) Å, 
hars/alpha.gif" BORDER=0> = 93.46(2)
, hars/beta2.gif" BORDER=0 ALIGN="middle"> = 93.68(2), hars/gamma.gif" BORDER=0 > = 109.0(3), V = 2387.4 Å3, and Z = 2. All of these complexes were found to be active toward oxidation of catechol byO2 in DMF at 20 C to afford intradiol cleavage products. The catechol was quantitatively oxidized, mainly(90%) into 3,5-di-tert-butyl-5-(carboxymethyl)-2-furanone. Reaction rates were measured, and for the first three(topologically similar) complexes, a correlation of the second-order kinetic constants k with the optical parametersof the two LMCT O(DBC) 
Fe(III) bands was found. In particular, k increases with the hars/epsilon.gif" BORDER=0 >max of the charge-transfer bands. The k value of the complex [(BQPA)FeIII(DBC)]+, containing a tripodal ligand, is smaller thanexpected on the basis of these correlations. This discrepancy could be related to steric hindrance induced by theBQPA ligand. However, the much lower activity of the bispicen-Fe(III)-type complexes compared to that of the[(TPA)FeIII(DBC)]+ complex synthesized by Jang et al. (J. Am. Chem. Soc. 1991, 113, 9200-9204), despitesimilar hars/epsilon.gif" BORDER=0 >max values, shows that a knowledge of optical and NMR parameters values is not sufficient to explain thedioxygenase activity rate. In their study of protocatechuate 3,4-dioxygenase, Orville et al. (Biochemistry 1997,36, 10052-10066) suggested that asymmetric chelation of the catecholate to Fe(III) is of great importance in theefficiency of the intradiol dioxygenase reaction. Indeed, a comparison of the X-ray structures of [(TPA)FeIII(DBC)]+ and [(bispicMe2en)FeIII(DBC)]+ shows that the Fe(III)-O bonds differ by 0.019 Å in the former andare identical in the latter. Asymmetry could also play a role in the model complexes. An alternative explanationis the possible existence of a low-spin state for [(TPA)FeIII(DBC)]+, as recently identified in [(TPA)FeIII(cat)]+by Simaan et al. (Angew. Chem., Int. Ed. Engl. 2000, 39, 196-198).
hars/alpha.gif" BORDER=0> = 93.46(2), hars/beta2.gif" BORDER=0 ALIGN="middle"> = 93.68(2), hars/gamma.gif" BORDER=0 > = 109.0(3), V = 2387.4 Å3, and Z = 2. All of these complexes were found to be active toward oxidation of catechol byO2 in DMF at 20 C to afford intradiol cleavage products. The catechol was quantitatively oxidized, mainly(90%) into 3,5-di-tert-butyl-5-(carboxymethyl)-2-furanone. Reaction rates were measured, and for the first three(topologically similar) complexes, a correlation of the second-order kinetic constants k with the optical parametersof the two LMCT O(DBC) Fe(III) bands was found. In particular, k increases with the hars/epsilon.gif" BORDER=0 >max of the charge-transfer bands. The k value of the complex [(BQPA)FeIII(DBC)]+, containing a tripodal ligand, is smaller thanexpected on the basis of these correlations. This discrepancy could be related to steric hindrance induced by theBQPA ligand. However, the much lower activity of the bispicen-Fe(III)-type complexes compared to that of the[(TPA)FeIII(DBC)]+ complex synthesized by Jang et al. (J. Am. Chem. Soc. 1991, 113, 9200-9204), despitesimilar hars/epsilon.gif" BORDER=0 >max values, shows that a knowledge of optical and NMR parameters values is not sufficient to explain thedioxygenase activity rate. In their study of protocatechuate 3,4-dioxygenase, Orville et al. (Biochemistry 1997,36, 10052-10066) suggested that asymmetric chelation of the catecholate to Fe(III) is of great importance in theefficiency of the intradiol dioxygenase reaction. Indeed, a comparison of the X-ray structures of [(TPA)FeIII(DBC)]+ and [(bispicMe2en)FeIII(DBC)]+ shows that the Fe(III)-O bonds differ by 0.019 Å in the former andare identical in the latter. Asymmetry could also play a role in the model complexes. An alternative explanationis the possible existence of a low-spin state for [(TPA)FeIII(DBC)]+, as recently identified in [(TPA)FeIII(cat)]+by Simaan et al. (Angew. Chem., Int. Ed. Engl. 2000, 39, 196-198).