Controlling selectivity in the reductive activation of CO₂ by mixed sandwich uranium(iii) complexes

Abstract

The uranium complexes [U(η8-C8H6(1,4-SiMe3)2)(η5-CpMe4R)] can be tuned to selectively reduce CO2, giving U(iv) complexes incorporating bridging oxo, carbonate, or oxalate groups.

Carbon Dioxide Activation by a Uranium(III) Complex Derived from a Chelating Bis(aryloxide) Ligand

“…Complex 6 shows an irreversible reduction wave at −2.19 V vs FeCp2 +/0 ( Figure S4) which is in excellent agreement with the quasi-reversible process at −2.18 V vs FeCp2 +/0 seen in 3 and is assigned to the U IV /U III couple in this system. This value is similar to other U IV /U III redox couples found in other U III systems studied by us and others 10,21 and is consistent with a strongly reducing metal center. Further supporting this assignment is the observation of a single quasi-reversible reduction process at −2.19 V vs FeCp2 +/0 in the dinuclear U(IV) complex, 4 ( Figure S2).…”

“…solvent-free) has recently been reported as a potentially high yielding and selective approach to exploring subsequent reduction chemistry. 19 Recent work from our own laboratory has used supercritical CO2 to promote the exclusive formation of U(IV) bridging carbonate complexes, 10 and this approach was used to investigate the reductive activation of CO2 by 3 (Scheme 3). The reaction of solid 3 in supercritical CO2 resulted in an immediate color change from green-black to orange, and the resultant orange powder contained only one major product (>96% by 1 H NMR spectroscopy), confirming the highly selective nature of the reaction.…”

Activation of Heteroallenes COxS2–x (x = 0–2): Experimental and Theoretical Evidence of the Synthetic Versatility of a Bulky Guanidinato SmII Complex

“…This C-S bond formation is reminiscent of the C-O bond formation reported by Castro et al in carbonate formation in U III and Sm II chemistry. [30][31][32][33] How-ever, in the latter, after C-O bond formation, C-O bond cleavage occurred to form a CO molecule. Interestingly, in this study (Figure 3), C-S bond breaking is not observed, which strengthens the argument of the lack of stability of the CS molecule.…”

Lanthanides and actinides: Annual survey of their organometallic chemistry covering the year 2014

“…[164] Electrochemical studies on both the uranium(III) complexes and the dimeric uranium(IV) CO 2 reduction products have been carried out and all exhibited quasireversible redox processes. In particular, the similarities in the U(III)/U(IV) redox couples suggested that the selectivity in the outcome of CO 2 reductive activation by these complexes is steric in origin rather than electronic.…”

“…Three possible mechanisms have been identified, as illustrated in Sm III -CO 2 -Sm III Cp * 2 was also observed and was found to react with a second molecule of CO 2 to yield the corresponding bimetallic oxalate complex via C-C coupling (mechanism M3). [164] 2LU III + CO 2 LU IV -CO 2 The CASSCF methodology was used to calculate the ground state electron densities of a series of seven actinocenes, AnCOT, (An = Th-Cm, COT = η 8 -C 8 H 8 ). Topological analysis revealed increased values of the electron density at the An-C bond for An = Pa-Pu, suggesting enhanced covalent character in metal-ligand bonding for these complexes.…”