Reduction chemistry of the mixed ligand metallocene [(C5Me5)(C8H8)U]2(μ-C8H8) with bipyridines

The U4+ cyclooctatetraenyl complex, [(C5Me5)(C8H8)U]2(μ-C8H8), 1, reacts with two equiv of 4,4′-dimethyl-2,2′-bipyridine (Me2bipy) and 2 equiv of 2,2′-bipyridine (bipy) to form 2 equiv of (η5-C5Me5)(η8-C8H8)U(Me2bipy-κ2N,N′) and (η5-C5Me5)(η8-C8H8)U(bipy-κ2N,N′), respectively. X-ray crystallography, infrared spectroscopy, and density functional theory calculations indicate that the products are best described as U4+ complexes of bipyridyl radical anions. Hence, only one of the (C8H8)2− ligands in 1 acts as a reductant and delivers 2 electrons per equiv of 1. Since the reduction potentials of uncomplexed (C8H8)2−, Me2bipy, and bipy are −1.86, −2.15, and −2.10 V vs SCE, respectively, it is likely that prior coordination of the bipyridine reagents enhances the electron transfer.