Metalation of Pyrrole-Based NNN-Pincer Ligands with Heteroaromatic Donor Substituents

Abstract

Enzymes are extremely effective biological catalysts and are exemplary models for the design of smaller molecular catalysts. Inspired by such frameworks, we synthesized the pincer ligands 2,5-bis((1H-pyrazol-1-yl)methyl)-1H-pyrrole (pyr-NNN-pyz) and 2,5-Bis((1H-1,2,4-triazol-1-yl)methyl)-1H-pyrrole (pyr-NNN-trz), and performed metalation reactions with palladium and nickel in attempt to synthesize products of the form M(pyr-NNN-R)Cl (M = Ni, Pd; R = pyz, trz). Conditions such as solvent, atmosphere, and use of a base were changed in order to find optimum metalation conditions. Products of these reactions were primarily analyzed using 1H NMR spectroscopy. Thus far, tridentate coordination of the ligand has not been confirmed, though an asymmetric product has been observed. Many complexes containing heterocyclic aromatic-NNN pincer ligands are proficient at catalyzing reactions such as a proton-coupled electron transfer (PCET) reaction. In addition to considering such reactions, we will attempt to invoke metal-ligand cooperation through hydrogenation/dehydrogenation-type reactions to discover new reaction pathways.