Direct Synthesis of Ligand-Based Radicals by the Addition of Bipyridine to Chromium(II) Compounds

The reaction of 2,2′-bipyridine (bpy) with monomeric chromium­(II) precursors was used to prepare the <i>S</i> = 1 complexes Cr­(tBu-acac)₂(bpy) (<b>1</b>) and (η⁵-Cp)­(η¹-Cp)­Cr­(bpy) (<b>3</b>), as well as the <i>S</i> = 2 compound Cr­[N­(SiMe₃)₂]₂(bpy) (<b>4</b>). The crystallographically determined bond lengths indicate that the bpy ligands in <b>1</b> and <b>3</b> are best regarded as radical anions, while <b>4</b> shows no structural evidence for electron transfer from Cr^II to the neutral bpy ligand