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

Abstract

Complexes of type [Re ^V L(NC ₆ H ₄ Y-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-XC ₆ H ₄ NH ₂ (X = Me or Cl). Treatment with aqueous nitric acid in acetonitrile converts them into [Re ^VI L′(NC ₆ H ₄ Y-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(NC ₆ H ₄ Cl)Cl ₃ ] and [ReL′(NC ₆ H ₄ Cl)Cl ₃ ] (X = Me in both cases) revealed the presence of severely distorted and meridionally configured ReCl ₃ N ₃ co-ordination spheres. The effective metal radius decreases only marginally upon metal oxidation and the imide fragment is approximately linear and triple bonded, ReN–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.