# Syntheses and Reactivity of Yb and Sm Inverse Sandwich Arene Complexes

## TL;DR

This paper explores how rare earth metal complexes react with different arene ligands, showing that reactivity depends on the metal's oxidation state and the charge on the bridging benzene anion.

## Contribution

The study reveals distinct reactivity patterns of Yb and Sm inverse sandwich complexes based on their oxidation states and ligand interactions.

## Key findings

- YbII complexes reacted with various arenes to form new YbII complexes with bridging ligands.
- SmIII complexes only reacted with easily reducible substrates like anthracene and COT.
- In situ reduced SmI complexes formed SmIII-arene4−-SmIII complexes with toluene and similar substrates.

## Abstract

Inverse sandwich arene complexes of rare earth metals have gained notable interest due to their unique electronic properties. In these complexes, an arene ligand bridges two metal centres, storing 0, 2, or 4 electrons, which is the basis for unique reactivity. Herein, we report on the reactivity of [(DIPePBDI)Ln]2(η
6,η
6‐benzene) (II‐Ln, Ln = Yb or Sm) and in situ reduced [(DIPePBDI)SmI]2 (V) (DIPePBDI = HC[C(Me)N‐DIPeP]2, DIPeP = 2,6‐CHEt2‐phenyl). The YbII‐benzene2−‐YbII complex (II‐Yb) reacted smoothly with biphenyl, naphthalene, anthracene, and COT, giving a range of new YbII complexes with bridging arene or COT ligands. However, due to much stronger Sm‐arene bonding in II‐Sm, which should be regarded as a SmIII‐benzene4−‐SmIII complex, this reagent only reacted with substrates that can be reduced easily (anthracene and COT). Interestingly, reaction with anthracene gave a SmII‐anthracene2−‐SmII complex, showing that the benzene4− is able to reduce SmIII to SmII. In situ reduced [(DIPePBDI)SmI]2 (V) can be considered a (DIPePBDI)SmI synthon, which reacted smoothly with toluene, biphenyl, or 1,3,5‐triphenyl‐benzene and affords a series of SmIII‐arene4−‐SmIII complexes. However, reaction with pyrene gave an SmII‐pyrene2−‐SmII product. All complexes have been fully characterized with X‐ray diffraction.

The reactivity of inverse sandwich lanthanide benzene complexes depends strongly on the metal oxidation states and consequently, the charge on the bridging benzene anion. Whereas the YbII complex reacted as a 2e donor with biphenyl, naphthalene, anthracene and COT, the strongly bound SmIII complex only reacted with anthracene and COT.