Concomitant Carboxylate and Oxalate Formation From the Activation of CO₂ by a Thorium(III) Complex

Abstract

Improving our comprehension of diverse CO2 activation pathways is of vital importance for the widespread future utilization of this abundant greenhouse gas. CO2 activation by uranium(III) complexes is now relatively well understood, with oxo/carbonate formation predominating as CO2 is readily reduced to CO, but isolated thorium(III) CO2 activation is unprecedented. We show that the thorium(III) complex, [Th(Cp′′)3] (1, Cp′′={C5H3(SiMe3)2‐1,3}), reacts with CO2 to give the mixed oxalate‐carboxylate thorium(IV) complex [{Th(Cp′′)2[κ2‐O2C{C5H3‐3,3′‐(SiMe3)2}]}2(μ‐κ2:κ2‐C2O4)] (3). The concomitant formation of oxalate and carboxylate is unique for CO2 activation, as in previous examples either reduction or insertion is favored to yield a single product. Therefore, thorium(III) CO2 activation can differ from better understood uranium(III) chemistry.

A Relativistic DFT Probe of Thorium and Protactinium Complexes Supported by Heterocalix[4]arene and Redox Properties of Early‐Middle Actinides

“…In contrast, the Th(III) complex remains rare due to the greatly negative reduction potential −2.35 V (vs. Fc + /Fc), where 0.65 V was used to correct the original value (vs. NHE) . Although recent advance in the synthetic technique leads to more accessibility of Th III complexes, the study of redox properties of Th VI /Th III complexes remains underexplored, to our best of knowledge. For example, above E 0 of Th VI/III ions in water is the only available value, and moreover was obtained with the assistance of electron‐transfer and f ‐ d absorption bands .…”

“…The molecular chemistry of thorium is dominated by the IV oxidation state in contrast to III and II ones. Although extremely low reduction potentials of Th IV/III (‐3.0 V versus NHE) and Th III/II (‐4.9 V) were presumed, several Th III complexes and even one Th II complex have been synthesized and structurally characterized via massive efforts . In addition to commonly used cyclopentadienyl (Cp), cyclooctatetraenyl (COT) and their substituted derivatives, a small‐cavity macrocyclic trans ‐calix[2]pyrrole[2]benzene (H 2 L, Figure ), synthesized by the Sessler's group, has been found suitable for chelating Th IV .…”

Computational Comparative Mechanistic Study of C−E (E=C,N,O,S) Coupling Reactions through CO2 Activation Mediated by Uranium(III) Complexes

“…The reported homogeneous catalytic systems mainly rely on the d ‐transition metal complexes . In recent years, to benefit from their ability to adopt multiple oxidation states and their reducibility at low oxidation states, researchers in this field have expanded their studies to the 5 f elements, among which are the trivalent uranium complexes …”

“…The study of these catalytic systems is therefore of fundamental importance to understand the role of 5 f orbitals in homogeneous catalysis, and contributes to the evaluation and rational design of new types of catalytic systems. Computational tools have been used to gain mechanistic insights into U III ‐mediated CO 2 activation …”

“…The reportedh omogeneous catalytic systems mainly rely on the d-transition metal complexes. In recent years, to benefitf rom their ability to adopt multiple oxidation states and their reducibility at low oxidation states,r esearchers in this field have expandedtheir studies to the 5f elements, [22][23][24][25][26][27][28][29] amongw hich are the trivalenturanium complexes. [30][31][32][33][34] In trivalentu ranium complexes, the electron-richUatom is protected by bulky ligands [30,35] such as the hydrotris(3,5-dimethylpyrazolyl)-borate ligand (Tp*), which is ab ulky Lewis base, [36,37] and the complexese xist as salts.…”