A Mild Protocol To Generate Uranium(IV) Mixed-Ligand Metallocene Complexes using Copper(I) Iodide

Reaction of the trivalent uranium complexes (C5Me5)(2)UI(THF) (1), (C5Me5)(2)U[N(SiMe3)(2)] (3), (C5Me5)(2)U(NPh2)(THF) (4), and (C5Me5)(2)U(O-2,6-Pr-i(2)-C6H3)(THF) (5) with copper(I) iodide affords the corresponding tetravalent uranium diiodide, amide iodide, and aryloxide iodide complexes (C5Me5)(2)UI2 (2), (C5Me5)(2)U[N(SiMe3)(2)](I) (6), (C5Me5)(2)U(NPh2)(I) (7) and (C5Me5)(2)U(O-2,6-Pr-i(2)-C6H3)(I) (8), respectively. This protocol was also extended to the synthesis of the alkyl iodide complex (C5Me5)(2)U(CHPh2)(I) (10). The isolation of complex 10 from the in situ generated trivalent uranium alkyl complex (C5Me5)(2)U(CHPh2)(THF) (9) illustrates the synthetic value of this oxidation procedure in those situations where the uranium(III) metallocene complex cannot be isolated or is unstable. Overoxidation and ligand redistribution are not observed with this Cu-based U-III -> U-IV oxidation procedure. Attempted functionalization of the U-IV amide iodide complex (C5Me5)(2)U[N(SiMe3)(2)](I) (6) with Me2Mg afforded the novel azametallacycle (C5Me5)(2)U[eta(2)(N,C)-CH2SiMe2N(SiMe3)] (12) by intramoiecular C-H activation and liberation of methane. Reaction between (C5Me5)(2)U(NPh2)(I) (7) and Me2Mg afforded a mixture of the products (C5Me5)(2)U(NPh2)(Me) (13), (C5Me5)(2)UMe2 (14), and (C5Me5)(2)U(NPh2)(2) (15) at room temperature; heating the mixture smoothly furnished the azametallacycle (C5Me5)(2)U[eta(2)(N,C)-(o-C6H4)NPh] (16). Similarly, reaction between 14 and HNPh2 at 100 degrees C produced the azametallacycle 16 by aminolysis and subsequent intramolecular C-H activation.