Syntheses and Reactivity Studies of Square-Planar Diamido–Pyridine Complexes Based on Earth-Abundant First-Row Transition Elements

The new square-planar complexes M­[NNN]­(pyridine)
(M = Fe (1), Co­(2); NNN = 2,6-bis­(2,6-diisopropylphenylamidomethyl)­pyridine)
were synthesized and fully characterized to investigate small molecule
activation on this platform and also associated ligand innocence.
The equatorial pyridine solvent moiety could not be removed; a new
bis-ligand species Co­[NNN.H]2 (3) was synthesized
in low yield while attempting to make the base-free derivative. Attempts
to prepare the Ni analogue of 1 and 2 instead
yielded crystals of a di-imino–pyridine complex Ni­[PDI]Cl (4) (PDI = 2,6-bis­(2,6-diisopropylphenyliminomethyl)­pyridine),
following loss of methylene backbone hydrogen atoms. Structural analysis
indicates that the PDI ligand is a mono-anionic radical. This susceptibility
of the ligand to oxidative dehydrogenation was also shown when the
reaction of 2 with 2 equiv of trityl chloride yielded
a new complex with an asymmetric imino–amino pyridine ligand
Co­[NNN′]­Cl2 (5) (NNN′ = 2-(2,6-(diisopropylphenyliminomethyl)-6-(diisopropylphenylamidomethyl)-pyridine)
in good yield.