Ytterbocenes as One‐ and Two‐Electron Reductants in their Reactions with Diazadienes: Yb III Mixed‐Ligand Bent‐Sandwich Complexes Containing a Dianion of Diazabutadiene

Ytterbocene [Yb(C 5 MeH 4 ) 2 (thf) 2 ] reacts with diazabutadiene 2,6‐ i Pr 2 C 6 H 3 NCHCHNC 6 H 3 i Pr 2 ‐2,6 (DAD) as a one‐electron reductant to afford a bis(cyclopentadienyl) Yb III derivative containing a DAD radical anion [Yb(C 5 MeH 4 ) 2 (dad −. )]. However, ytterbocenes [YbCp* 2 (thf) 2 ] (Cp*=C 5 Me 5 , C 5 Me 4 H) coordinated by sterically demanding cyclopentadienyl ligands act as two‐electron reductants in their reactions with DAD. These reactions occur by abstraction of one Cp* ring and result in the formation of novel Yb III mixed‐ligand bent‐sandwich complexes, [YbCp*(dad)(thf)], in which the dianion of DAD has an uncommon terminal η 4 ‐coordination to the ytterbium atom. The variable‐temperature magnetic measurements of complex [Yb(C 5 Me 5 )(dad)(thf)] suggest the existence of redox tautomerism for this compound.