Incorporation of Tellurium into a NNN Pincer Ligand Framework and Consequences on Coordination Behavior

Secondary bonding interactions such as hydrogen-bonding have emerged as beneficial design elements in the construction of molecular catalysts. Here we examine the incorporation of chalcogen-bonding units in the form of benzotellurazole moieties into an NNN chelating framework. A series of substituted 2,6-bis(benzotellurazole)pyridines (NNN^R, R = H, ^tBu, CF₃, and Me) have been synthesized through double deoxygenative cyclization of pyridine diamide precursors. The new NNN^R species are fully characterized in solution and the solid state and demonstrate planar structures consistent with related pyridine-bis(benzoxazole) chelates. Coordination complexes of Fe and Mn have been identified and structurally characterized demonstrating intermolecular chalcogen bonding between Te and Cl. Despite this promise, the compounds display very low solubility in common solvents and are found to readily demetalate in the presence of coordinating solvents. To investigate the factors contributing to the weak metal binding, density functional theory calculations are performed. The calculations demonstrate unfavorable energetics associated with the planar syn,syn conformation required for metal binding, which is a consequence of steric interactions between the pyridine unit and the large Te atoms of the benzotellurazole.