Exploring the effect of the LnIII/LnII redox potential on C–F activation and on oxidation of some lanthanoid organoamides

Abstract

The divalent europium complexes, [Eu(L^Me/Et)₂(thf)₂] and [Eu(L^Et)₂(dme)] (L^Me/Et = p-HC₆F₄N(CH₂)₂NMe₂/Et₂), have been prepared from redox-transmetallation/protolysis (RTP) reactions between Eu metal, Hg(C₆F₅)₂ and L^Me/EtH in thf. The complexes exhibit close (C)F–Ln interactions and the amide ligands feature tridentate N,N′,F chelation. The complexes are thermally robust but on exposure to light they undergo C–F activation. From exposure of [Eu(L^Et)₂(thf)₂] to light, the Eu^III mixed fluoride/oxide cluster, [Eu₄(L^Et)₆F₂O₂] was isolated, but other well-defined C–F activation products have proven elusive due to the stability of Eu^II. Oxidation of [Ln(L^R)₂(thf)₂] (Ln = Eu, R = Me; Ln = Yb, R = Et) with I₂ afforded the heteroleptic iodo complexes, [Ln(L^R)₂I(thf)_n] (Ln = Eu, n = 1; Ln = Yb, n = 0), and the homoleptic complexes, [Ln(L^R)₃]. The formation of the iodo complexes and the heteroleptic complexes appear to occur by different routes. [Yb(L^Et)₃] shows interesting structural differences from reported [Ln(L^Et)₃] (Ln = La, Ce, Nd) complexes, and highlights an incomplete shift towards N,N′ chelation to the much smaller Yb ion. [Sm(L^Me)₃] was prepared from a protolysis reaction between [Sm(CH₂C₆H₄-NMe₂-o)₃] and L^MeH. Heating a solution of [Sm(L^Me)₃] in toluene at 110 °C for three days did not afford any samarium fluoride complex. An RTP reaction with Sm afforded the heteroleptic samarium complex, [Sm(L^Me)₂F]₃, in very low yield. From an attempted protolysis reaction between [Sm(DippForm)₂(thf)₂] and L^MeH, the mixed ligand samarium fluoride complex, [Sm(DippForm)(L^Me)F]₂, was isolated. Overall, the instability of Sm^II precludes control over the C–F activation reactions.