Tris(pyridyl)borates: an emergent class of versatile and robust polydentate ligands for catalysis and materials applications.

Tridentate ligands that incorporate pyridyl rather than pyrazolyl groups are emerging as an attractive class of "scorpionate"-type ligands with enhanced electron donation, increased stability, and divergent geometry at the metal centre relative to tris(pyrazolyl)borates originally introduced by Trofimenko. Following our initial reports, the tris(pyridyl)borate (Tpyb) ligand architecture has been adopted by several research groups in pursuit of functional metal complexes that offer new opportunities in catalysis and materials science. While earlier work had been focused on symmetric octahedral complexes, ML 2 , which are advantageous as highly robust building blocks in materials sciences, recently introduced new ligand designs provide access to heteroleptic metal complexes with vacant sites that lend themselves to applications in catalysis. Signficant progress has also been made in the post-complexation functionalization of these ligands via electrophilic and nucleophilic substitution reactions at the boron centres, opening up new routes for integration of Tpyb complexes with diverse functional materials while also raising interesting mechanistic questions.