Facile ligand oxidation and ring nitration in ruthenium complexes derived from a ligand with dicarboxamide-N and phosphine-P donors.

The reaction of the tetradentate dicarboxamide ligand 1,2-bis-N-[2'(diphenylphosphanyl)benzoyl]diaminobenzene (dppbH(2)) with RuCl(3) in DMF or ethanol results in metal-mediated ligand oxidation and formation of the diamagnetic Ru(II) complex [(dppQ)Ru(Cl)(2)] (1) with N(2)P(2) chromophore. The o-phenylenedicarboxamide portion of the dppb(2-) ligand is oxidized to a o-benzoquinonediimine (bqdi) moiety in [(dppQ)Ru(Cl)(2)]. Presence of oxygen accelerates the ligand oxidation process. Unlike other tetradentate dicarboxamide ligands with pyridine-N, phenolato-O, or thiolato-S donors, dppb(2-) provides stability to the +2 oxidation state of ruthenium and facilitates oxidation of the coordinated ligand frame. Results of spectroscopic and redox studies strongly support the +2 oxidation state of Ru in 1. Exposure of 1 to NO(g) does not lead to formation of any metal nitrosyl; instead, the bqdi ring is nitrated to afford [(NO(2)dppQ)Ru(Cl)(2)] (2).