Functionalized pyridine in pyclen-based iron(iii) complexes: evaluation of fundamental properties

Abstract

Six iron(iii) pyridinophane complexes were evaluated to determine whether functionalizing the pyridine ring could introduce a handle by which electrochemical properties and thermodynamic stability can be tuned.

Recent progress in the chemistry of 12-membered pyridine-containing tetraazamacrocycles: from synthesis to catalysis

“…In line with their previous studies with OH-substituted pyclen derivatives (see Scheme 2), [10][11][12][13] Green's group also reported the synthesis of di-hydroxyl macrocyclic pyridinophane L40. 55 The ligand L40 was prepared by dimerization of 4-benzyloxy-2,6-bis-(chloromethyl)pyridine (2a) with tosyl amide 74 (Scheme 17).…”

“…As expected, the presence of the hydroxyl moiety significantly enhanced the antioxidant activity. Moreover, their chelation abilities were demonstrated with the preparation of several ions from transition [10][11][12] and group 2 metals. 13 A related contribution from Green's group focused on providing methodology for the synthesis of pyclen macrocycles bearing electron-withdrawing groups at position 4 on the pyridine ring (Scheme 3).…”

“…13 A related contribution from Green's group focused on providing methodology for the synthesis of pyclen macrocycles bearing electron-withdrawing groups at position 4 on the pyridine ring (Scheme 3). 12,14 Conventional methodologies were employed to prepare the required 4-substituted bis-(2,6-bromomethyl)pyridine derivatives 4a-d, whose better solubility with respect to chloro analogues ensured a more efficient cyclization. Moreover, the selection of the protected triamines 1 relied on the functional group compatibility for the deprotection step.…”

Mechanistic Insights into Iron-Catalyzed C–H Bond Activation and C–C Coupling

“…However, an acylperoxo-Fe­(III) in equilibrium with oxo-Fe IV and Fe V is formed when [FeL4­(OTf) 2 ] is exposed to an oxidant. ,, To further support this, iron hydroxides form readily . The Fe III (OH) species of the L1–L3 complexes is likely present in pyrrole, based on speciation curve-derived potentiometric studies that indicate that this species is present at pH values >∼8.5. The Fe III (OH) species could readily oxidize to higher valent species, which is supported by our DFT and experiments by others. , Therefore, due to the ambiguity of the oxidation states (Fe IV vs Fe V ) within the active catalytic cycle, both possibilities are represented (Scheme ).…”

“…20,21,78 To further support this, iron hydroxides form readily. 79 The Fe III (OH) species of the L1−L3 complexes is likely present in pyrrole, based on speciation curve-derived potentiometric studies 80 that indicate that this species is present at pH values >∼8.5. The Fe III (OH) species could readily oxidize to higher valent species, which is supported by our DFT and experiments by others.…”