Activation of SO₂ and CO₂ by Trivalent Uranium Leading to Sulfite/Dithionite and Carbonate/Oxalate Complexes

Abstract

The first sulfite [{(((nP,Me) ArO)3 tacn)U(IV) }2 (μ-κ(1) :κ(2) -SO3 )] (tacn=triazacyclononane) and dithionite [{(((nP,Me) ArO)3 tacn)U(IV) }2 (μ-κ(2) :κ(2) -S2 O4 )] complexes of uranium from reaction with gaseous SO2 have been prepared. Additionally, the reductive activation of CO2 was investigated with respect to the rare oxalate [{(((nP,Me) ArO)3 tacn)U(IV) }2 (μ-κ(2) :κ(2) -C2 O4 )] formation. This ultimately provides the unique S2 O4 (2-) /C2 O4 (2-) and SO3 (2-) /CO3 (2-) complex pairs. All new complexes were characterized by a combination of single-crystal X-ray diffraction, elemental analysis, UV/Vis/NIR electronic absorption, IR vibrational, and (1) H NMR spectroscopy, as well as magnetization (VT SQUID) studies. Moreover, density functional theory (DFT) calculations were carried out to gain further insight into the reaction mechanisms. All observations, together with DFT, support the assumption that SO2 and CO2 show similar (dithionite/oxalate) to analogous (sulfite/carbonate) activation behavior with uranium complexes.

Magnesium(I) Dimers Bearing Tripodal Diimine–Enolate Ligands: Proficient Reagents for the Controlled Reductive Activation of CO2 and SO2

“…Another reason for exploring this chemistry was that a series of lanthanide metal(II) and uranium(III) compounds were recently shown to reductively couple SO 2 to give dithionite, [S 2 O 4 ] 2− , complexes, (cf., the formation of II and 13 ) 15. 16 In view of the emerging analogies between magnesium(I) systems and low‐valent f‐block metal systems, it seemed reasonable that magnesium(I) compounds could yield related magnesium dithionite complexes, crystallographically characterized examples of which are currently unknown. Indeed, to our knowledge, the only structurally authenticated examples of any discreet molecular main group dithionite compound are a silicon(IV) species, accessed by reduction of SO 2 with a silicon(II) compound,17 and Sn 2 (S 2 O 4 ) 2 18…”

A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO2

“…DFT calculations suggested a peculiar reaction path (Scheme ), being very different from the one found for samarocenes or trivalent uranium complexes 3d,e. Here, the CO 2 moiety of the metastable intermediate dimetalloxycarbene 5′ (“ Int‐a ”, Scheme ) directly attacks free CO 2 in a nucleophilic manner known from carbene chemistry 29.…”

Mixed sandwich imido complexes of Uranium(V) and Uranium(IV): Synthesis, structure and redox behaviour

“…U1-N1 (Å) 1.935(7) 1.964(5) 1.980 4R-N1-U1 (˚) 172.6(4) 171.7 (4) 168.4 4Ct(COT)-U (Å) 1.979 71.999(1) 1.983 6Ct(Cp*)-U (Å) 2.500(1) 2.515 32.474 9Ct(COT)-U-Ct(Cp*) (˚) 133.71 3133.76 9136.16 3Table 1: Comparison of key metric parameters of complexes (2), 3and 4.…”

“…Low valent actinide (essentially uranium and thorium) chemistry has attracted significant attention, both from a purely academic viewpoint but also in the context of activation of important small molecules. 1 Examples of the latter include CO cyclo-oligomerisation, 2 CO2 3 and SO2 4 reductive coupling, NO/CO co-disproportionation, 5 CO/H2 coupling, 6 N2 activation, 7 and electro-catalytic splitting of H2O promoted by sterically encumbered U(III) complexes. 8 The common denominator amongst all these examples is that they employ the An(III)/An(IV) (An = the other hand, uranium complexes in oxidation state (IV) exhibit reactivity attributed mainly to the insertion of reactive molecules (CO, CO2) into U(IV)-X (X = C, H, heteroatom), 9 although there are examples of U(III) alkyl complexes with bulky substituents that will also undergo such reactivity rather than promote a redox event.…”