Iron Substitution for Sodium in a Carboxylate-Bridged, Heterodinuclear Sodium−Iron Complex

• Published in: Journal of the American Chemical Society 2005-11, Vol.127 (46), p.16004-16005
• Main Authors: Kodanko, Jeremy J, Xu, Dong, Song, Datong, Lippard, Stephen J
• Format: Article
• Language: English
• Subjects: Carboxylic Acids - chemistry; Chemistry; Coordination compounds; Exact sciences and technology; Inorganic chemistry and origins of life; Iron - chemistry; Molecular Structure; Preparations and properties; Sodium - chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja054943d

The synthesis and structural characterization of the carboxylate-bridged, heterodinuclear iron−sodium complex [NaFe(PIC2DET)(μ-O2CTrp)3] (2), where PIC2DET (1) is a 2,3-diethynyltriptycene-linked dipicolinic methyl ester ligand and Trp is 9-triptycenyl, are described. The metal ions in 2 are bridged by three triptycene carboxylates with an Fe···Na distance of 3.181(2) Å, and each is coordinated to a pyridine nitrogen and carbonyl oxygen atom of 1, forming two five-membered chelate rings. A linkage isomer in which Fe1 is bound by the other ester oxygen atom of 1 was identified by X-ray crystallographic analysis. Treatment of 2 with Fe(OTf)2·2MeCN resulted in substitution of sodium by iron(II) to give the cationic diiron(II) complex [Fe2(PIC2DET)(μ-O2CTrp)3][OTf] (3). This reaction was investigated by UV−vis, IR, MS, and stopped-flow spectroscopy. The substitution is first order with respect to 2 and zero order with respect to Fe(OTf)2·2MeCN (k obs = 21 ± 2 s-1), consistent with a dissociative mechanism. A positive enthalpy of activation (ΔH ⧧ = 59 ± 6 kJ mol-1) and negative entropy of activation (ΔS ⧧ = −20 ± 6 J mol-1 K-1) were calculated from the temperature dependence of the rate-determining dissociation step.