Metalloradical Compounds with 1,2‐Dipivaloylhydrazido Ligands: Electron Transfer and Alkylation/Protonation Effects

Under oxidative conditions the complexes M(bpy) 2 Cl 2 , M = Ru or Os, react with 1,2‐dipivaloylhydrazine H 2 L = t BuC(O)‐NH‐NH‐C(O)‐ t Bu to yield the paramagnetic compounds [M(L)(bpy) 2 ](PF 6 ) { 1 (PF 6 ), M = Ru and 2 (PF 6 ), M = Os}. Crystal structures of 1 (ClO 4 ) and 2 (PF 6 ) reveal an NNCO chelate coordination of L with d (NN) ≈ 1.39 Å. EPR spectroscopy suggests a metal/ligand mixed situation for the unpaired electron, with 29 % (Ru, 1 + ) or 46 % (Os, 2 + ) metal spin contribution according to DFT calculations. Both complex cations exhibit reversible one‐electron oxidation and reduction ( K c ≈ 10 19 for 1 + and 10 12 for 2 + ) which could also be monitored by IR (ν CO ) and UV/Vis‐NIR spectroelectrochemistry. These data confirm a metal/ligand orbital mixing M II (L · – ) ↔ M III (L 2– ), with the osmium analogue favoring the latter alternative. Reaction of Ru(bpy) 2 Cl 2 under non‐oxidizing conditions yields the intermediate ( 1 H)(PF 6 ) which could be oxidatively deprotonated to 1 + or methylated to ( 1 Me)(PF 6 ), both identified by 1 H and 13 C NMR. While oxidation of ( 1 H) + proceeds irreversibly due to proton loss, the reversible spectroelectrochemical oxidation of ( 1 Me) + suggests a metal‐based process Ru II (LMe – ) → Ru III (LMe – ). The results reveal that not only dinuclear complexes of 1,2‐diacylhydrazido ligands but also mononuclear analogues are distinguished by remarkably variable metal/ligand mixed contributions to the frontier orbitals.