Small-Molecule Activation Mediated by a Uranium Bipyridyl Metallocene

Addition of potassium
graphite (KC8) to a solution of
(η5-C5Me5)2UCl2 (1) and 2,2′-bipyridine (bipy) gives
the uranium bipyridyl metallocene (η5-C5Me5)2U­(bipy) (2) in good yield.
In complex 2 a bipy radical anion is coordinated to a
U­(III) atom, and it is therefore an ideal starting material for small-molecule
activation: e.g., it serves as a synthetic equivalent for the (η5-C5Me5)2UII fragment
on treatment with conjugated alkynes and a variety of heterounsaturated
molecules such as imines, carbodiimide, organic azides, hydrazine,
and azo derivatives. Alternatively, it may also react with aldehydes,
ketones, nitriles, and α,β-unsaturated reagents such as p-ClPhCHO, (CH2)5CO, PhCN, and methyl
methacrylate (MMA), forming the C–C bond coupling products
(η5-C5Me5)2U­[(bipy)­(p-ClPhCHO)] (10), (η5-C5Me5)2U­[(bipy)­{(CH2)5CO}] (11), (η5-C5Me5)2U­[(bipy)­(PhCN)] (12), (η5-C5Me5)2U­[(bipy)­{CH2C­(Me)­CO­(OMe)] (13a), and [(η5-C5Me5)2U­{OC­(OMe)C­(Me)­CH2–3-bipy}]2 (13b), respectively,
in quantitative conversion. Furthermore, addition of CuI to complex 2 induces a single-electron-transfer process to form the uranium­(III)
iodide complex (η5-C5Me5)2U­(I)­(bipy) (14).