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. 2022 Feb 21;61(7):3249-3255.
doi: 10.1021/acs.inorgchem.1c03744. Epub 2022 Feb 7.

Exploring the Redox Properties of Bench-Stable Uranyl(VI) Diamido-Dipyrrin Complexes

Karlotta van Rees  1 , Emma K Hield  1 , Ambre Carpentier  2 , Laurent Maron  2 , Stephen Sproules  3 , Jason B Love  1
Affiliations

Exploring the Redox Properties of Bench-Stable Uranyl(VI) Diamido-Dipyrrin Complexes

Karlotta van Rees et al. Inorg Chem. .

Abstract

The uranyl complexes UO2(OAc)(L) and UO2Cl(L) of the redox-active, acyclic diamido-dipyrrin anion L- are reported and their redox properties explored. Because of the inert nature of the complexes toward hydrolysis and oxidation, synthesis of both the ligands and complexes was conducted under ambient conditions. Voltammetric, electron paramagnetic resonance spectroscopy, and density functional theory studies show that one-electron chemical reduction by the reagent CoCp2 leads to the formation of a dipyrrin radical for both complexes [Cp2Co][UO2(OAc)(L•)] and [Cp2Co][UO2Cl(L•)].

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Structures of uranyl(VI) di-imine and dipyrrin complexes.
Scheme 1
Scheme 1. Synthesis of HL
Reaction conditions: (i) neat tBuNH2, reflux, 16 h; (ii) 0.5 equiv of C6F5CHO, 5 mol % p-TSA, PhCH3, reflux, 16 h; (iii) 1.1 equiv of DDQ, THF, RT, 24 h.
Scheme 2
Scheme 2. Synthesis of Uranyl Complexes of HL
Reaction conditions: (i) 1.1 equiv of UO2(OAc)2·2H2O or UO2Cl2(THF)2, NEt3, MeOH/CHCl3 (1:3, v/v), heated to reflux in air for 16 h; (ii) 1.5 equiv of KH under N2, THF, RT, 16 h, followed by the addition of UO2Cl2(THF)2; (iii) 1 equiv of CoCp2, THF, RT, 16 h.
Figure 2
Figure 2
X-ray crystal structure of HL viewed from the side and top. For clarity, all hydrogen atoms except those involved in hydrogen bonding are omitted (displacement ellipsoids are drawn at 50% probability).
Figure 3
Figure 3
X-ray crystal structures of UO2(OAc)(L) (a and c) and UO2Cl(L) (b and d) viewed from the side and top. For clarity, all hydrogen atoms except on amide N1 and N4 are omitted (displacement ellipsoids drawn at 50% probability).
Figure 4
Figure 4
Stacked CVs for HL, UO2(OAc)(L) and UO2Cl(L). All measured as 1 mM MeCN solutions (0.1 M [nBu4N][PF6] supporting electrolyte, glassy-carbon working electrode, platinum gauze counter electrode, and silver wire quasi-reference electrode). Potentials are referenced against the Fc/Fc+ couple recorded under identical conditions.
Figure 5
Figure 5
UV–vis spectra of HL in CH2Cl2, UO2(OAc)(L) and UO2Cl(L) in THF, and [Cp2Co][UO2(OAc)(L•)] and [Cp2Co][UO2Cl(L•)] in pyridine.
Figure 6
Figure 6
Molecular orbital plots of UO2(OAc)(L) (a and b) and UO2Cl(L) (d and e) and spin-density plots of the singly reduced complexes [UO2(X)(L•)]− (c and f). The ISO value is 0.02 au. Hydrogen atoms were omitted for clarity. Positive is purple; negative is red. All energies are depicted in kilocalories per mole.
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