Ring Nitrogenation of Aromatic Amines by the Excited State of an Osmium(VI) Nitrido Complex.

The reactivity of electrophilic Os VI and Ru VI nitrides toward various aliphatic and aromatic amines have been previously reported; these reactions all go through an initial nucleophilic addition of the amine nitrogen to M VI ≡N (M = Os, Ru) to generate a M IV hydrazido species. Herein, we report that the excited state of a luminescent osmium(VI) nitrido complex, [Os VI (N)( L )(CN) 3 ] - ( OsN , HL = 2-(2-hydroxy-5-nitrophenyl)benzoxazole), undergoes unprecedented ring nitrogenation of aromatic amines. Visible-light irradiation of OsN generates OsN* , which predominantly attacks the aromatic ring of 2,6-dimethylaniline (Me 2 PhNH 2 ) to give an Os(II) benzoquinone diimine compound (PPh 4 )[Os II ( L )(CN) 3 ( p -NH═Me 2 Ph═NH 2 )] [ (PPh 4 )2 ] in 60% yield, while nucleophilic addition of the amine N to OsN* also occurs to give the osmium(II) diazonium compound (PPh 4 )[Os II ( L )(CN) 3 (N = N-Me 2 Ph)] [ (PPh 4 )1 ] as a minor product (10% yield). On the other hand, OsN* undergoes exclusive ring nitrogenation of diphenylamine, indole, and carbazole to give the corresponding osmium(II) benzoquinone diimines. All products have been characterized by various spectroscopic techniques and by X-ray crystallography. The reaction between OsN* and Ar 2 N is proposed to proceed via an initial 1e - transfer (ET) followed by proton transfer (PT) to generate Os V NH and Ar 2 N • intermediates, which then further combine to give the product. The benzoquinone diimine ligands are susceptible to oxidation. Oxidation of 2 with H 2 O 2 at ambient conditions affords [Os IV ( L )(CN) 3 (N═PhMe 2 (O)═O)] - , which bears the previously unknown (epoxy)benzoquinone iminato ligand.