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

Complexes of type [(ReL)-L-V(NC6H4Y-p)Cl-3] (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 [(ReL)-L-VI'(NC6H4Y-p)Cl-3], 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)Cl-3] and [ReL'(NC6H4Cl)Cl-3] (X = Me in both cases) revealed the presence of severely distorted and meridionally configured ReCl3N3 do-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 approximate to 1.0 and approximate to 0.2 V respectively.