Synthesis of U(iv) imidos from Tp*2U(CH2Ph) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) by extrusion of bibenzyl

Abstract

Addition of organic azides, N₃R (R = 2,4,6-trimethylphenyl (Mes), phenyl (Ph), 1-adamantyl (Ad)), to a solution of the uranium(III) alkyl complex, Tp*₂U(CH₂Ph) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) (1), results in the formation of a family of uranium(IV) imido derivatives, Tp*₂U(NR) (2-R). Notably, these complexes were synthesized in high yields by coupling of the benzyl groups to form bibenzyl. The uranium(IV) imido derivatives, 2-Mes, 2-Ph, and 2-Ad, were all characterized by both ¹H NMR and IR spectroscopy, and 2-Mes and 2-Ad were also characterized by X-ray crystallography. In the molecular structure of 2-Mes, typical κ³-coordination of the Tp* ligands was observed; however in the case of 2-Ad, one pyrazole ring of a Tp* ligand has rotated away from the metal centre, forcing a κ²-coordination of the pyrazoles. This results in a uranium–hydrogen interaction with the Tp* B–H. Treating these imido complexes with para-tolualdehyde results in multiple bond metathesis, forming the terminal uranium(IV) oxo complex, Tp*₂U(O), and the corresponding imine.