Unusual Reactivity of Methylene Group Adjacent to Pyridine-2-Carboxamido Moiety in Iron(III) and Cobalt(III) Complexes

The Fe(III) and Co(III) complexes of the ligand N-(2-picolyl)picolinamide (pmpH; H represents the dissociable amide
hydrogen), namely, [Fe(pmp)2]BF4 (1) and [Co(pmp)2]ClO4 (2), have been synthesized and structurally characterized.
The −CH2− moiety of pmp- in [M(pmp)2]+ (M = Fe, Co) is very reactive and is readily converted to carbonyl
(CO) group upon exposure to dioxygen. Such conversion results in [M(bpca)2]ClO4 complexes (M = Fe (3), Co
(5); bpcaH = bis(2-pyridylcarbonyl)amine) which have been characterized by spectroscopy and X-ray diffraction.
The structure of 5 is reported here for the first time. The reactivity of the −CH2− moiety of pmp- has so far
precluded the isolation of 1 although other metal complexes of pmp- have been reported years ago. The CH2 →
CO transformation arises from the tendency of the coordinated pmp- ligand to achieve further conjugation in the
ligand framework and provides a better way to synthesize the metal complexes of bpcaH ligand. Reaction of 3 with
NaH affords Fe(II) complex [Fe(bpca)2] (4) without any reduction of the ligand frame.