Pyridine-2-carboxamide complexes of arylimidorhenium(VI) derived from 2-pyridylmethyleneamine complexes of arylimidorhenium(V) via oxygen-atom transfer

Complexes of type [Re^VL(NC₆H₄Y-p)Cl₃] (Y = H or Cl) have been synthesized where L is the Schiff base formed from pyridine-2-carbaldehyde and the aniline p-XC₆H₄NH₂ (X = Me or Cl). Treatment with aqueous nitric acid in acetonitrile converts them into [Re^VIL′(NC₆H₄Y-p)Cl₃], where L′ is a monoanionic pyridine-2-carboxamide. The latter complexes display hyperfine-split six-line solution EPR spectra at room temperature. The crystal structures of [ReL(NC₆H₄Cl)Cl₃] and [ReL′(NC₆H₄Cl)Cl₃] (X = Me in both cases) revealed the presence of severely distorted and meridionally configured ReCl₃N₃ co-ordination spheres. The effective metal radius decreases only marginally upon metal oxidation and the imide fragment is approximately linear and triple bonded, Re≡N-C, in both cases. The rhenium(VI)-rhenium(V) reduction potentials in the two types of complex are ≈1.0 and ≈0.2 V respectively.