STABILIZATION OF URANIUM(IV) ALKYLS BY BULKY CHELATING LIGANDS - MOLECULAR-STRUCTURE OF [PHC(NSIME3)2]3UME

Chelate ligand-stabilized uranium sigma-methyl complexes are obtained in good yields by treatment of [RC6H4C(NSiMe3)2]3UCl (1) with methyllithium. The molecular structure of [PhC(NSiMe3)2]3UMe (3a) has been determined by X-ray crystallography. A long uranium - carbon bond [249.8(5) pm] indicates steric crowdinq in the molecule. Analogously the dimethyluranium complex [(CF3)3C6H2C(NSiMe3)2]2UMe2 (4b) is prepared from [(CF3)3C6H2C(NSiMe3)2]2UCl2 and two equivalents of methyllithium. Reaction of 1 with NaBH4 yields the tetrahydroborates [RC6H4C(NSiMe3)2]3UBH4 (5). The strongly temperature-dependent H-1-NMR spectra of the complexes 1 and 3 have been studied in detail.