Electronic Perturbations of Iron Dipyrrinato Complexes via Ligand β-Halogenation and meso-Fluoroarylation

Abstract

Systematic electronic variations were introduced into the monoanionic dipyrrinato ligand scaffold via halogenation of the pyrrolic β-positions and/or via the use of fluorinated aryl substituents in the ligand bridgehead position in order to synthesize proligands of the type 1,9-dimesityl-β-R(4)-5-Ar-dipyrrin [R = H, Cl, Br, I; Ar = mesityl, 3,5-(F(3)C)(2)C(6)H(3), C(6)F(5) in ligand 5-position; β = 2,3,7,8 ligand substitution; abbreviated ((β,Ar)L)H]. The electronic perturbations were probed using standard electronic absorption and electrochemical techniques on the different ligand variations and their divalent iron complexes. The free-ligand variations cause modest shifts in the electronic absorption maxima (λ(max): 464-499 nm) and more pronounced shifts in the electrochemical redox potentials for one-electron proligand reductions (E(1/2): -1.25 to -1.99 V) and oxidations (E(1/2): +0.52 to +1.14 V vs [Cp(2)Fe](+/0)). Installation of iron into the dipyrrinato scaffolds was effected via deprotonation of the proligands followed by treatment with FeCl(2) and excess pyridine in tetrahydrofuran to afford complexes of the type ((β,Ar)L)FeCl(py) (py = pyridine). The electrochemical and spectroscopic behavior of these complexes varies significantly across the series: the redox potential of the fully reversible Fe(III/II) couple spans more than 400 mV (E(1/2): -0.34 to +0.50 V vs [Cp(2)Fe](+/0)); λ(max) spans more than 40 nm (506-548 nm); and the (57)Fe Mössbauer quadrupole splitting (|ΔE(Q)|) spans nearly 2.0 mm/s while the isomer shift (δ) remains essentially constant (0.86-0.89 mm/s) across the series. These effects demonstrate how peripheral variation of the dipyrrinato ligand scaffold can allow systematic variation of the chemical and physical properties of iron dipyrrinato complexes.

Ground State and Excited State Tuning in Ferric Dipyrrin Complexes Promoted by Ancillary Ligand Exchange

“…10 The present work illustrates a far more dramatic effect on the observed electrochemical properties upon examination of 4 – 6 . Substitution of the chloride ancillary ligands in 4 with the more electron-rich tert -butoxide ligands shows an increased stabilization of the Fe III oxidation state by cyclic voltammetry, where each alkoxide substitution cathodically shifts the Fe III/II couple by 600 mV.…”

Synthesis, characterization and C–H amination reactivity of nickel iminyl complexes

“…37 The uorinated aryl meso-substituent on the dipyrrin anodically shis the bound transition metal and provides a useful 19 F handle for 19 F NMR characterization. 45 Metalation of ( AdF L)H with Ni followed previously reported protocols for preparing Fe and Co congeners. 37,42,44 Lithiation of ( AdF L)H is carried out by adding PhLi as a solid to a frozen benzene solution of ( AdF L)H. 37,44 The addition of resultant ( AdF L)Li in THF to a frozen solution of NiCl 2 (py) 2 in THF afforded a dark-red, paramagnetic product.…”

Bifunctional Catalysts for CO2 Reduction

“…Systematic electronic variations were introduced into the monoanionic dipyrrin ligand scaffold via halogenation of the pyrollic β-positions and/or use of fluorinated aryl substituents in the ligand bridgehead position yielding ligands of the type ( β,Ar L)H. 7 The electronic perturbations were probed using standard electronic absorption and electrochemical techniques on the different ligand variations and their divalent iron complexes. The electrochemical and spectroscopic behavior of the iron-bound complexes varies significantly across the series; most notably the redox potential of the fullyreversible Fe III/II couple spans more than 400 mV as electron-withdrawing substituents are appended to the dipyrromethene platform ( Figure 3 left panel).…”