Unexpected dispersion-stabilized tris(terphenylthiolate) complexes, Ln(SAriPr6)3, arising from two-electron reduction by Ln(SAriPr6)2 [AriPr6 = C6H3-2,6-(C6H2-2,6,4-iPr3)2]

Abstract

The first examples of a M(EAr^iPr6)₃ complex [Ar^iPr6 = C₆H₃-2,6-(C₆H₂-2,4,6-ⁱPr₃)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.