Tetrazine Chelate Ligands Bridging Two [Ru(acac)₂] Fragments: Mixed Valency and Radical Complex Formation

Abstract Using bis(3‐methyl‐2‐pyridyl)‐1,2,4,5‐tetrazine 1 , 3‐(2‐pyrimidyl)‐6‐methyl‐1,2,4,5‐tetrazine 2 and bis(2‐pyrimidyl)‐1,2,4,5‐tetrazine=bmtz as ligands, the complexes 3 =[Ru(acac) 2 ( 1 )], 4 ={[Ru(acac) 2 ] 2 ( 1 )], 5 ={[Ru(acac) 2 ] 2 (bmtz)], and 6 ={[Ru(acac) 2 ] 2 ( 2 )] were prepared and identified by structure analysis of crystallized material. The one‐electron oxidized form 6 (PF 6 ) was also studied structurally, suggesting a Class II mixed‐valent situation. The neutral dinuclear systems exhibit two reversible oxidation processes with comproportionation constants 10 9.2 < K c <10 14.1 and one reduction which were analyzed UV/vis/NIR and EPR spectroscopically. Oxidation produces largely metal‐based mixed‐valent cations with very weak intervalence absorptions in the near IR whereas the electron uptake occurs at the tetrazine acceptor.