title: Triptycene-based Bis(benzimidazole) Carboxylate-Bridged Biomimetic Diiron(II) Complexes.
abstract: A triptycene-based bis(benzimidazole) ester ligand,L3, was designed to enhance the electron donating ability of the heterocyclic nitrogen atoms relative to those of the first generation bis(benzoxazole) analogs,L1andL2. A convergent synthesis ofL3was designed and executed. Three-component titration experiments using UV-visible spectroscopy revealed that the desired diiron(II) complex could be obtained with a 1:2:1 ratio ofL3:Fe(OTf)2(MeCN)2:external carboxylate reactants. X-ray crystallographic studies of two diiron complexes derived in this manner fromL3revealed their formulas to be [Fe2L3(μ-OH)(μ-O2CR)(OTf)2], where R = 2,6-bis(p-tolyl)benzoate (7) or triphenylacetate (8). The structures are similar to that of a diiron complex derived fromL1, [Fe2L1(μ-OH)(μ-O2CArTol)(OTf)2] (9) with a notable difference being that, in7and8, the geometry at iron more closely resembles square-pyramidal than trigonal-bipyramidal. Mössbauer spectroscopic analyses of7and8indicate the presence of high-spin diiron(II) cores. These results demonstrate the importance of substituting benzimidazole for benzoxazole for assembling biomimetic diiron complexes with syn disposition of twoN-donor ligands, as found in O2-activating carboxylate-bridged diiron centers in biology.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.forename: Chan Myae
authors.initials: CM
authors.lastname: Myae Soe
authors.forename: Justin J
authors.initials: JJ
authors.lastname: Wilson
authors.forename: Suan Lian
authors.initials: SL
authors.lastname: Tuang
authors.forename: Ulf-Peter
authors.initials: UP
authors.lastname: Apfel
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Lippard