Iron(III) complexes of certain meridionally coordinating tridentate ligands as models for non-heme iron enzymes: the role of carboxylate coordination

Dhanalakshmi, Thirumanasekaran ; Bhuvaneshwari, Mookkan ; Palaniandavar, Mallayan (2006) Iron(III) complexes of certain meridionally coordinating tridentate ligands as models for non-heme iron enzymes: the role of carboxylate coordination Journal of Inorganic Biochemistry, 100 (9). pp. 1527-1534. ISSN 0162-0134

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S01620...

Related URL: http://dx.doi.org/10.1016/j.jinorgbio.2006.05.004

Abstract

The iron(III) complexes [Fe(pda)Cl(H2O)2] (1), [Fe(tpy)Cl3] (2), and [Fe(bbp)Cl3] (3), where H2pda is pyridine-2,6-dicarboxylic acid, tpy is 2,2':6,2"-terpyridine and bbp is 2,6-bis(benzimidazolyl)pyridine, have been isolated and studied as functional models for the intradiol-cleaving catechol dioxygenase enzymes. Mixed ligand complexes of H2pda with the bidentate ligands 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) have been also prepared and studied. All the complexes have been characterized using absorption spectral and electrochemical methods. The spectral changes in the catecholate adducts of the complexes generated in situ have been investigated. Upon interacting the complexes with catecholate anions a low energy catecholate to iron(III) charge transfer band appears, which is similar to that observed for enzyme-substrate complexes. All the complexes catalyze the oxidative intradiol cleavage of 3,5-di-tert-butylcatechol (H2dbc) in the presence of dioxygen. Interestingly, on replacing the pyridyl groups in 2 and the bulky benzimidazole groups in 3 by the carboxylate groups, the yields of the intradiol cleavage products of dioxygenation increases, 1 (50%) > 2 (20%) > 3 (10%). The higher intradiol yield for 1 has been ascribed to the meridional coordination of two carboxylate groups of pda2-. In contrast to the trend in the intradiol cleavage yields, a tremendous decrease in the rate (200 times) is observed on replacing the two pyridyl moieties in 2 by two carboxylates as in 1 and a significant decrease in rate is observed on replacing the pyridyl moieties in 2 by strongly σ -donating benzimidazole moieties as in 3. This is in conformity with the decrease in Lewis acidities of the iron(III) centers.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Iron(III) Complexes; Tridentate; Meridional Coordination; Carboxylate Donors; Intradiol Cleavage
ID Code:30958
Deposited On:27 Dec 2010 06:55
Last Modified:05 Mar 2011 05:42

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