Synthesis, structure and redox properties of single-atom bridged diuranium complexes supported by aryloxides

Single-atom (group 15 and group 16 anions) bridged dimetallic complexes of low oxidation state uranium provide a convenient route to implement multielectron transfer and promote magnetic communication in uranium chemistry, but remain extremely rare. Here we report the synthesis, redox and magnetic properties of N3-, O2-, and S2- bridged diuranium complexes supported by bulky aryloxide ligands. The U(iv)/U(iv) nitride [Cs(THF)8][(U(OAr)3)2(mu-N)], 1 could be prepared and characterized but could not be reduced. Reduction of the neutral U(iv)/U(iv) complexes [(U(OAr)3)2(mu-X)] A (X = O) and B (X = S) led to the isolation and characterization of the U(iv)/U(iii) and U(iii)/U(iii) analogues. Complexes [(K(THF)4)2(U(OAr)2)2(mu-S)2], 5 and [K(2.2.2-cryptand)]2[(U(OAr)3)2(mu-S)], 6 are the first examples of U(iii) sulphide bridged complexes. Computational studies and redox properties allow the reactivity of the dimetallic complexes to be related to their electronic structure. Reduction of the neutral UIV-X-UIV (X = O or S) complexes supported by aryloxide ligands yielded the UIV/UIII and UIII/UIII analogues. Notably, UIII-S-UIII is the first example of a U(iii) sulphide-bridged complex.