Syntheses and Reactivity Studies of Square-Planar
Diamido–Pyridine Complexes Based on Earth-Abundant First-Row
Transition Elements
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Abstract
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]<sub>2</sub> (<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′]Cl<sub>2</sub> (<b>5</b>) (NNN′ = 2-(2,6-(diisopropylphenyliminomethyl)-6-(diisopropylphenylamidomethyl)-pyridine)
in good yield