Triptycene‐Based, 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, L1 and L2. A convergent synthesis of L3 was 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 of L3:Fe(OTf)2(MeCN)2:external carboxylate reactants. X-ray crystallographic studies of two diiron complexes derived in this manner from L3 revealed 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 from L1, [Fe2L1(μ-OH)(μ-O2CArTol)(OTf)2] (9) with a notable difference being that, in 7 and 8, the geometry at iron more closely resembles square-pyramidal than trigonal-bipyramidal. Mössbauer spectroscopic analyses of 7 and 8 indicate 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 two N-donor ligands, as found in O2-activating carboxylate-bridged diiron centers in biology.

A Family of Tri- and Dimetallic Pyridine Dicarboxamide Cryptates: Unusual O,N,O-Coordination and Facile Access to Secondary Coordination Sphere Hydrogen Bonding Interactions

“…In contrast to the sulfide- or oxide-bridged clusters, the diiron, tricopper, and heme-iron–copper active sites of the bacterial monooxygenases, multicopper oxidases, and cytochrome c oxidase, respectively, display weak interactions between the metal centers in the reduced state, but substrate binding activates cooperativity between the metal centers. − ,,, , A number of groups have developed self-assembled and designed ligands to model these active sites; , however, these systems display limited a priori control of the metal–metal distance or are unable to probe the role of proximal hydrogen bonding interactions. In addition, few examples have been reported in which hydrogen bonding interactions are incorporated into dinucleating ligands …”

Copper‐ and Palladium‐Cocatalyzed Intramolecular C–H Functionalization/C–N Bond Formation: A Route to the Synthesis of Indoloisoquinoline Derivatives

“…Lippard’s research program is centered around bioinorganic chemistry, including platinum anticancer drugs, diiron complexes, bacterial multicomponent monooxygenases, and inorganic neurotransmitters and signal transducers. He has reported in the European Journal of Inorganic Chemistry on biomimetic diiron complexes 10 …”

Empfänger der National Awards 2014 der American Chemical Society

“…Sein Forschungsprogramm hat als Schwerpunkt die bioanorganische Chemie, einschließlich Platin‐Zytostatika, Dieisenkomplexe, bakterielle Mehrkomponenten‐Monooxygenasen sowie anorganische Neurotransmitter und Signalgeber. Er hat im European Journal of Inorganic Chemistry biomimetische Dieisenkomplexe vorgestellt 10 …”