Unprecedented Pyrazine-Bridged Guanidinate Rare Earth Complexes Through a Bridge Splitting Reaction Path

The development of reaction pathways and ancillary ligand scaffolds is essential in the pursuit of higher nuclearity rare earth metal clusters that are relevant in storage materials and catalysis. Guanidinate anions represent attractive ligands due to their high degree of customizability allowing for facile alterations of both their steric and electronic properties. Here, we demonstrate an unprecedented bridge splitting reaction that shifts chloride anions in favor of a bridging neutral pyrazine to give pyrazine-bridged dinuclear guanidinate rare earth complexes, [{(Me3Si)2NC(NiPr)2}2RECl]2(mu-pyz) (RE =Y (1) and Er (2), pyz=pyrazine). Each six-coordinate metal center is ligated by two guanidinates, one chloride ligand, and one nitrogen atom from the bridging pyrazine unit. The molecules were characterized by X-ray crystallography, IR, NMR, and UV-Vis spectroscopy. DFT calculations conducted on 1 provide insight into both the bonding picture and the mechanism of complex formation. This type of reaction constitutes a seminal application of a bridge splitting mechanism to the rare earth metals. Two dinuclear pyrazine-bridged rare earth complexes were synthesized through a bridge splitting reaction, and unambiguously characterized by X-ray crystallography, spectroscopy, and computations. The cyclic voltammograms reveal multiple redox features which are attributed to the bridging pyrazine ligand. These materials represent promising building blocks for the development of supramolecular systems. image