Synthesis and structures of ruthenium di‐ and tricarbonyl complexes derived from 4,5‐diazafluoren‐9‐one

Carbon monoxide (CO) has recently been shown to impart beneficial effects in mammalian physiology and considerable research attention is now being directed toward metal–carbonyl complexes as a means of delivering CO to biological targets. Two ruthenium carbonyl complexes, namely trans‐dicarbonyldichlorido(4,5‐diazafluoren‐9‐one‐κ²N,N′)ruthenium(II), [RuCl₂(C₁₁H₆N₂O)(CO)₂], (1), and fac‐tricarbonyldichlorido(4,5‐diazafluoren‐9‐one‐κN)ruthenium(II), [RuCl₂(C₁₁H₆N₂O)(CO)₃], (2), have been isolated and structurally characterized. In the case of complex (1), the trans‐directing effect of the CO ligands allows bidentate coordination of the 4,5‐diazafluoren‐9‐one (dafo) ligand despite a larger bite distance between the N‐donor atoms. In complex (2), the cis disposition of two chloride ligands restricts the ability of the dafo molecule to bind ruthenium in a bidentate fashion. Both complexes exhibit well defined ¹H NMR spectra confirming the diamagnetic ground state of Ru^II and display a strong absorption band around 300 nm in the UV.