Tuning the Diiron Core Geometry in Carboxylate-Bridged Macrocyclic Model Complexes Affects Their Redox Properties and Supports Oxidation Chemistry

Abstract

We introduce a novel platform to mimic the coordination environment of carboxylate-bridged diiron proteins by tethering a small, dangling internal carboxylate, (CH)COOH, to phenol-imine macrocyclic ligands (HPIMICn). In the presence of an external bulky carboxylic acid (RCOH), the ligands react with [Fe(Mes)] (Mes = 2,4,6-trimethylphenyl) to afford dinuclear [Fe(PIMICn)(RCO)(MeCN)] (n = 4-6) complexes. X-ray diffraction studies revealed structural similarities between these complexes and the reduced diiron active sites of proteins such as Class I ribonucleotide reductase (RNR) R2 and soluble methane monooxygenase hydroxylase. The number of CH units of the internal carboxylate arm controls the diiron core geometry, affecting in turn the anodic peak potential of the complexes. As functional synthetic models, these complexes facilitate the oxidation of C-H bonds in the presence of peroxides and oxo transfer from O to an internal phosphine moiety.

Coordinating Ability of Anions, Solvents, Amino Acids, and Gases towards Alkaline and Alkaline‐Earth Elements, Transition Metals, and Lanthanides

“…[47] In one case, the presence of MeCN but not THF coordinated to Fe in two binuclear complexes was observed in am ixture of the two solvents, and was attributedt ot he betterc oordinating ability of MeCN. [48] However,s uch an explanation must be taken with ag rain of salt, since the differencei nc oordinating ability indicesb etween these two solvents is within the expectedu ncertainty.…”

The crystal structure of [Fe2(PIMIC6)(AnthCO2)(CH3CN)]·[Fe2(PIMIC6)(AnthCO2)(CH3CN)0.9(CH2Cl2)0.1]·[Fe2(PIMIC6)(AnthCO2)(OH2)]·0.75CH3CN: a crystallographer's nightmare or a fascinating case of disorder?

“…Hydrogen atoms as well as minor occupied disorder components are omitted for clarity. between dichloromethane and the diiron core with distances of 3.230 (3), 2.885 (3), 3.168 (3) and 2.922 (3) Å were observed (Wang et al, 2017). Other than that, there are no reports about iron-dichloromethane interactions.…”

“…Based on a free refinement of the occupancy its value was constrained to 90% to generate a less complicated sum formula. Lippard and coworkers (including the author of this publication) recently published the crystal structure of (2) and related complexes (Wang et al, 2017). There, similar non-covalent interactions Arrangement of the three discrete complex molecules in the asymmetric unit and assignment of residues 1-3.…”

“…Crystals of (1) were obtained by slow re-crystallization of the air-sensitive complex [Fe 2 (PIMIC6)(AnthCO 2 )(CH 3 CN)] (Wang et al, 2017) [(2), Fig. 1] from a mixture of CH 3 CN and CH 2 Cl 2 (DCM) in a glove box with nitrogen atmosphere.…”

“…Large red blocks suitable for X-ray structure analysis could be harvested after six months. The crystals were cooled with dry ice and handled under a CO 2 atmosphere during preparation and mounting because of the air sensitivity of (2) and solvent loss observed in (2) and related compounds (Wang et al, 2017).…”