Carbon Dioxide Reduction by Multimetallic Uranium(IV) Complexes Supported by Redox-Active Schiff Base Ligands

Marta Falcone, Nadir Jori, Marinella Mazzanti, Rosario Scopelliti
AMER CHEMICAL SOC, 2020
Journal paper

Abstract

The synthesis, structure, and reactivity with CO2 and CS2 of new U(IV) complexes with a redox-active Schiff base are reported. The reaction of UI3 with the heptadentate Schiff base ligand 2,2',2 ''-tris(salicylideneimino)-triethylamine (trensal) did not lead to the formation of a U(III) complex but to the reductive coupling and C-C bond formation between two imino groups of the Schiff base, yielding the U(IV) complex [U-2(bis-trensal)], 1. Further reduction of 1 led to the dinuclear macrocyclic complex [{K(THF)(3)}(2)U-2(cyclotrensal)], 3-THF, through a second C-C bond formation reaction between two additional imino groups. Complexes 1 and 3 are oxidized by AgOTf resulting in the cleavage of the C-C bonds and leading to the formation of the U(IV) complex [U(trensal)]OTf, 2. Complex 1 does not reduce CO2 or CS2 but undergoes insertion of CO2 into one of the U-N bonds. In contrast, the reaction of 3 with 2 equiv of CO2 leads to the reductive disproportionation of CO2 to afford carbonate in 80% yield. In the presence of a large excess of CO2 multiple reactions take place, as supported by the isolation of the crystals of [{K(THF)(3)}U-2(mu-O)(CO2-CO-cyclo-trensal)(U(trensal))], 4. The higher reductive activity toward CO2 of complex 3 compared to previously reported U(IV) complexes of reduced Schiff bases is interpreted in terms of its redox properties.

Official source

https://infoscience.epfl.ch/record/277932?ln=en

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related concepts

Related publications

, , ,

Here we have explored the ability of Schiff bases to act as electron reservoirs and to enable the multi-electron reduction of small molecules by lanthanide complexes. We report the reductive chemistry of the Ln(iii) complexes of the tripodal heptadentate Schiff base H(3)trensal (2,2 ',2 ''-tris(salicylideneimino)triethylamine), [Ln(III)(trensal)],1-Ln(Ln = Sm, Nd, Eu). We show that the reduction of the [Eu-III(trensal)] complex leads to the first example of a Eu(ii) Schiff base complex [{K(mu-THF)(THF)(2)}(2){Eu-II(trensal)}(2)],3-Eu. In contrast the one- and two-electron reduction of the [Nd-III(trensal)] and [Sm-III(trensal)] leads to the intermolecular reductive coupling of the imino groups of the trensal ligand and to the formation of one and two C-C bonds leaving the metal center in the +3 oxidation state. The resulting one- and two electron reduced complexes [{K(THF)(3)}(2)Ln(2)(bis-trensal)],2-Ln, and [{K(THF)(3)}(2){K(THF)}(2)Ln(2)(cyclo-trensal)],4-Ln(Ln = Sm, Nd) are able to effect the reductive disproportionation of carbon dioxide by transferring the electrons stored in the C-C bonds to CO(2)to selectively afford carbonate and CO. The selectivity of the reaction contrasts with the formation of multiple CO(2)reduction products previously reported for a U(iv)-trensal system.

ROYAL SOC CHEMISTRY2020

Transition-metal catalyzed C-H functionalizations have impacted and changed synthetic approaches towards the construction of relevant complex molecules, comprising natural products, active pharmaceutical ingredients, and organic materials. This thesis describes the development of Rh(III)-catalyzed reactions via directed C-H functionalization and non-directed C-H functionalization. In this respect, acylated sulfonamides and N-sulfonyl ketimines were successfully employed as suitable directing groups, enabling directed C-H bond activation in the presence of a rhodium(III) catalyst. Subsequent migratory insertion of internal alkynes delivered a rich array of versatile benzosultams and chiral spirocyclic sultams, both of which are relevant structures in medicinal chemistry. Notably, the use of rhodium(III) complexes equipped with a suitable atropchiral cyclopentadienyl ligand enables enantioselective and high yielding access to the challenging spirocyclic sultam scaffolds. Complementary to the directed C-H bond functionalizations, application of CpRh(III) complexes in non-directed C-H functionalization reactions have been disclosed. Specific applications of this challenging strategy include the synthesis of highly valuable polyarenes from completely unbiased arenes via double C-H activation, and subsequent addition of internal alkynes. This method provides a convenient handle to access highly substituted and highly soluble acenes, possessing valuable electronic and photo physical properties. Furthermore, non-directed C-H functionalization of electron-rich heterocycles was also developed. In this context, a CpRh(III) catalyst enables a C2-selective activation of heteroarenes. Upon addition across an alkyne, a transmetalation to Cu(II) allows reductive C-O bond formation to deliver tetrasubstituted enol esters in a trans-selective fashion. A three-component coupling of heteroarenes, alkynes, and carboxylic acids was successfully demonstrated.

EPFL2016

The synthesis, structure, and reactivity of a new complex of U(IV) with the tridentate Schiff base ligand Menaphtquinolen are reported. The reduction of the bis-ligand complexes [UX2(Menaphtquinolen) 2] (X = Cl, (1-Cl); I (1-I)) with potassium metal affords the U(IV) complex of the new tetranionic hexadentate ligand μ-bis- Menaphtquinolen formed through the intramolecular reductive coupling of the imino groups of each Menaphtquinolen unit. The solid state structure of the [U(μ-bis-Menaphtquinolen)]2 dimer 2 isolated from toluene confirms the presence of a U(IV) complex of the reduced ligand. Reactivity studies with molecular oxygen and 9,10-phenanthrenequinone show that complex 2 can act as a multielectron reducing agent releasing two electrons through the cleavage of the C-C bond to restore the original imino function of the ligand. In the resulting U(IV) and U(VI) complexes [U(9,10-phenanthrenediol)(Menaphtquinolen)2], 3, and [UO2(Menaphtquinolen)2], 4, the restored tridentate Schiff base allows for the coordination of the reduced substrate to the metal. Electrochemical studies of complex 2 show the presence of irreversible ligand centered reduction processes and of a reversible U(IV)/U(III) couple. © 2013 American Chemical Society.

2013