Ligand metalation in the reactivity of a tetravalent uranium amides

The reactions of organolithium reagents with the tetravalent UCl(2)[N(SiMe(3))(2)](2) and its DME solvate have been examined. Treatment of both compounds with methyl-lithium in diethyl ether resulted in one electron reduction of the metal center and gamma-deprotonation of one of the ligands. The dimeric {U[(mu-CH(2)-SiMe(2))N(SiMe(3))](2)[mu-Li(DME)]}(2) (1) was isolated from the reaction mixture regardless of the amount of MeLi employed. The employment of LiCH(2)SiMe(3) in DME led instead to multiple gamma-deprotonation events at the same carbon atom with formation of the trimetallic {U[(mu-CH(2)-SiMe(2))N(SiMe(3))][N(SiMe(3))(2)]}(2){U[(mu(3)-C-SiMe(2))N(SiMe(3))][N(SiMe(3))(2)]}{mu-OMe} (2) cluster centered on a fully deprotonated carbon atom. Crystallographic analysis revealed the presence of mu-OCH(3) units in the cluster as generated by DME solvent cleavage. A similar reaction carried out in the absence of DME led to the isolation of a closely related trimetallic {U[mu-(CH(2)-SiMe(2))N(SiMe(3))][N(SiMe(3))(2)]}(2){U[(mu(3)-C-SiMe(2))N(SiMe(3))][(mu-CH(2)-SiMe(2))N(SiMe(3))]} (3). One additional gamma-deprotonated fragment replacing the bridging methoxy group of 2 was present in this case. The presence of a fully deprotonated carbon atom bridging three metal centers and of one silicon atom was confirmed by both X-ray structures and NMR data. An attempt to reduce UCl(2)[N(SiMe(3))(2)](2) with KC(8) in a coordinating solvent resulted in ligand scrambling with the formation of two products. The first is a trimeric U(III) cluster formulated as {U-mu-Cl[N(SiMe(3))(2)][DME]}(2){U-mu-Cl[N(SiMe(3))(2)](2)}{mu(3)-Cl}(2) (4). The second was U[N(SiMe(3))(2)](3). A similar reduction reaction carried out in noncoordinating toluene resulted instead in an attack on the ligand affording the dimeric {U-mu-Cl[N(SiMe(3))(2)](2)[ horizontal lineN(SiMe(3))]}(2) (5). Alkylation of UCl(2)[N(SiMe(3))(2)](2) with n-butyl-lithium in hexane surprisingly yielded the pentavalent U[(mu-CH(2)-SiMe(2))N(SiMe(3))](2)[N(SiMe(3))(2)] (6). The acquisition of one additional ligand during the reaction hinted at the presence of other products in the reaction mixture.