Similarities and Differences in Benzene Reduction with Ca, Sr, Yb and Sm: Strong Evidence for Tetra‐Anionic Benzene

Abstract

Inverse sandwich complexes of Yb and Sm stabilized by a bulky b‐diketiminate (BDI) ligand have been prepared: (BDI)Ln(h6,h6‐C6H6)Ln(BDI); Ln = lanthanide. Coordinated benzene ligands can be neutral, di‐anionic or, often controversially discussed, even tetra‐anionic. The formal charge on benzene is correlated to assignment of the metal oxidation state which generally poses a problem. Herein, we take advantage of the structural similarities found when comparing CaII with YbII, and SrII with SmII complexes. In this work, we found an excellent overlap of the Ca/Yb inverse sandwich structures but a striking difference for the Sr/Sm pair. The much shorter Sm‐N and Sm‐C6H6 distances are strong evidence for a SmIII‐benzeneˉ4‐SmIII assignment. This was further supported by NMR spectrometry, magnetic susceptibility, reactivity and comprehensive computational investigation.

Correction: Neutral inverse-sandwich rare-earth metal complexes of the benzene tetraanion

“…For the samarium benzene complex [(BDI)Sm(THF)] 2 (μ-η 6 ,η 6 -C 6 H 6 ) ( 2-Sm ) reported in our article, two structurally related complexes [(BDI)Sm] 2 (μ-η 6 ,η 6 -C 6 H 6 ) and [(BDI Cy )Sm] 2 (μ-η 6 ,η 6 -C 6 H 6 ) (BDI Cy = CH[C(Me)NDicyp] 2 , Dicyp = 2,6-dicyclohexylphenyl) have been recently reported in ref. 1 and ref. 2 , respectively.…”