Cation-Mediated Conversion of the State of Charge in Uranium Arene Inverted-Sandwich Complexes
Résumé
Two new arene inverted‐sandwich complexes of uranium supported by siloxide ancillary ligands [K{U(OSi(OtBu)3)3}2(μ‐η6:η6‐C7H8)] (3) and [K2{U(OSi(OtBu)3)3}2(μ‐η6:η6‐C7H8)] (4) were synthesized by the reduction of the parent arene‐bridged complex [{U(OSi(OtBu)3)3}2(μ‐η6:η6‐C7H8)] (2) with stoichiometric amounts of KC8 yielding a rare family of inverted‐sandwich complexes in three states of charge. The structural data and computational studies of the electronic structure are in agreement with the presence of high‐valent uranium centers bridged by a reduced tetra‐anionic toluene with the best formulation being UV–(arene4−)–UV, KUIV–(arene4−)–UV, and K2UIV–(arene4−)–UIV for complexes 2, 3, and 4 respectively. The potassium cations in complexes 3 and 4 are coordinated to the siloxide ligands both in the solid state and in solution. The addition of KOTf (OTf=triflate) to the neutral compound 2 promotes its disproportionation to yield complexes 3 and 4 (depending on the stoichiometry) and the UIV mononuclear complex [U(OSi(OtBu)3)3(OTf)(thf)2] (5). This unprecedented reactivity demonstrates the key role of potassium for the stability of these complexes.