Pyridine diimine (PDI) ligands are a privileged scaffold that have been of large interest because of their redox-noninnocence. In conjunction with a metal center, the ligand can store additional electron density along its backbone that could assist in catalytic transformations. Expanding on previous work in these systems, we have altered the central pyridine ring of the ligand from an NNN donor architecture to an NCN pincer by inverting the pyridine ring. The N donors from the imines force the metal to bind in a meridional geometry and position the metal for the subsequent C-H activation. In the past, metalation of NCN pincers has been mostly limited to group 10 transition metals due to difficulty in activation of the C-H bond of the central aryl group for other transition metals. This hurdle, among others, has left this scaffold mostly unexplored on first-row transition metals. Changing the coordination environment of the metal can be used to alter the electronic nature of the complex from those known on the well-explored PDI systems and may lead to new reactivity. Inversion of the pyridine ring also provides an uncoordinated nitrogen at the 4-position of the ring. The para-nitrogen of the pyridine ring still has the potential to serve as a rich donor and provides the opportunity to functionalize the ligand with protons, Lewis acids, and/or alkyl groups. The addition of substituents at this site can be used to fine-tune the electronic properties of this system. Our lab is currently working on the synthesis and characterization of this new platform of pincer complexes.

Synthesis and characterization of an new class of redox-active pincer complexes

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