Unexpected dispersion-stabilized tris(terphenylthiolate) complexes, Ln(SAr ^iPr6)₃, arising from two-electron...

The first examples of a M(EAr ^iPr6)₃ complex [Ar ^iPr6 = C₆H₃-2,6-(C₆H₂-2,4,6- ⁱ Pr₃)₂] of any metal with any donor, E = O, S, NH, PH, have been isolated from the two-electron reduction of 1,3,5,7-cyclooctatetraene by the Ln(II) complexes Ln(SAr ^iPr6)₂ [Ln = La, Nd]. Two equiv. of Ln(SAr ^iPr6)₂ react with C₈H₈ to form the (C₈H₈)^2--ligated Ln(III) complexes, Ln(SAr ^iPr6)(C₈H₈). Surprisingly, the second product of this reaction is the tris(terphenylthiolate), Ln(SAr ^iPr6)₃, a complex expected to be too sterically crowded to exist. A computational study showed that interligand London dispersion effects (LDEs) in Ln(SAr ^iPr6)₃ are responsible for approximately half of the dissociation energy of the thiolate ligands. Overall, the results demonstrate that the (SAr ^iPr6)^1- ligand platform has a wide range of electronic and steric flexibility in rare-earth metal complexes.