Uranium-mediated reductive conversion of CO2 to CO and carbonate in a single-vessel, closed synthetic cycle

Abstract

The new neopentyl (Neop)-substituted tris(aryloxide) U(III) complex [(((Neop,Me)ArO)(3)tacn)U(III)] reacts with CO(2) to form CO and the bridging carbonate complex [{(((Neop,Me)ArO)(3)tacn)U(IV)}(2)(μ-CO(3))]. The uranium(IV) bridging oxo [{(((Neop,Me)ArO)(3)tacn)U(IV)}(2)(μ-O)] has been determined to be the intermediate in this reaction. For the first time, both U(iv) complexes can be reduced back to the U(III) starting material. Thus, with KC(8) as reductant, [(((Neop,Me)ArO)(3)tacn)U(III)] engages in a synthetic cycle, in which CO(2) is converted to CO and CO(3)(2-).

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

“…Accordingly, all new complexes show typical U IV magnetic behavior with minor ( 3 , 4 , and 7 ) to no temperature‐independent paramagnetism (TIP; 5 , 6 ) below 15 K. At 2 K, all complexes have low magnetic moment values varying from 0.50 to 0.67μ B per U, which is in good agreement with a non‐magnetic ground state and akin to other known U IV complexes 4a. 11, 15 Similar to other known tetravalent uranium complexes, all compounds possess comparable temperature‐dependent magnetic moments with initial steep increase up to 60 K, followed by a monotonic increase that results in room‐temperature‐obtained magnetic moments ranging from 2.43 to 2.69μ B per uranium center. These values are all significantly lower than the theoretical value of 3.58μ B .…”

“…The observed SO 2 uranium reactivity demonstrates remarkable similarity between uranium SO 2 and CO 2 activation chemistry. In analogy to the SO 2 activation chemistry, reaction with CO 2 led either to the recently reported carbonate complex [{(( nP,Me ArO) 3 tacn)U IV } 2 (mk 2 :k 2 -CO 3 )] (5) [11] or, under specific conditions, to the hitherto unknown uranium oxalate species [{(( nP,Me ArO) 3 tacn)U IV } 2 (mk 2 :k 2 -C 2 O 4 )] (7; Scheme 1). Similar to the procedure of the "single-vessel, closed synthetic cycle", [11] a 20 mL vial was charged with starting complex 1 dissolved in THF and excess KC 8 , the suspension was stirred over an atmosphere of CO 2 for several hours, and filtered over Celite.…”

“…In analogy to the SO 2 activation chemistry, reaction with CO 2 led either to the recently reported carbonate complex [{(( nP,Me ArO) 3 tacn)U IV } 2 (mk 2 :k 2 -CO 3 )] (5) [11] or, under specific conditions, to the hitherto unknown uranium oxalate species [{(( nP,Me ArO) 3 tacn)U IV } 2 (mk 2 :k 2 -C 2 O 4 )] (7; Scheme 1). Similar to the procedure of the "single-vessel, closed synthetic cycle", [11] a 20 mL vial was charged with starting complex 1 dissolved in THF and excess KC 8 , the suspension was stirred over an atmosphere of CO 2 for several hours, and filtered over Celite. Because compound 7 can be reduced slowly with KC 8 to form starting complex 1 and K 2 C 2 O 4 , the presence of K 2 C 2 O 4 in the filter cake was verified, by washing it with deuterated water and recording the 13 C NMR (see the Supporting Information).…”

“…The X-ray structures of complexes 3 and 5 reveal different coordination modes for the bridging SO 3 2À and CO 3 2À ligand (Figure 1, for more details about 5, see Ref. [11]). In contrast to the m-k 2 :k 2 -bound carbonate in 5, the sulfite in 3 coordinates in m-k 1 :k 2 fashion.…”

Synthesis of Differently Substituted tacn‐Based Ligands: Towards the Control of Solubility and Electronic and Steric Properties of Uranium Coordination Complexes

“…The reactions of these highly substituted lipophilic ligands with UCl 4 in the absence of base led directly to four isolable uranium(IV) chloro complexes [{( R1,R2 ArO) 3 tacn}U IV Cl] ( 14 ). In principle, the reduction of 14 with Na(Hg) or KC 8 should generate the analogous U III species,5h,16 which makes accessible uranium(III) complexes from conveniently available UO 3 · 2H 2 O17 as an “off‐the‐shelf” starting material as opposed to starting from valuable uranium metal (subject to occasional restricted supply) 25. The molecular structures of complexes 14 were determined and confirmed by 1 H NMR and UV/Vis spectroscopy, elemental analyses, SQUID magnetic susceptibility data, and single‐crystal X‐ray analyses.…”