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 (<b>1</b>), Co­(<b>2</b>); 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 (<b>3</b>) was synthesized in low yield while attempting to make the base-free derivative. Attempts to prepare the Ni analogue of <b>1</b> and <b>2</b> instead yielded crystals of a di-imino–pyridine complex Ni­[PDI]Cl (<b>4</b>) (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 <b>2</b> with 2 equiv of trityl chloride yielded a new complex with an asymmetric imino–amino pyridine ligand Co­[NNN′]­Cl₂ (<b>5</b>) (NNN′ = 2-(2,6-(diisopropylphenyliminomethyl)-6-(diisopropylphenylamidomethyl)-pyridine) in good yield