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.