Thorium- and Uranium-Mediated C–H Activation of a Silyl-Substituted Cyclobutadienyl Ligand

[Image: see text] Cyclobutadienyl complexes of the f-elements are a relatively new yet poorly understood class of sandwich and half-sandwich organometallic compounds. We now describe cyclobutadienyl transfer reactions of the magnesium reagent [(η(4)-Cb'''')Mg(THF)(3)] (1), where Cb'''' is tetrakis(trimethylsilyl)cyclobutadienyl, toward thorium(IV) and uranium(IV) tetrachlorides. The 1:1 stoichiometric reactions between 1 and AnCl(4) proceed with intact transfer of Cb'''' to give the half-sandwich complexes [(η(4)-Cb'''')AnCl(μ-Cl)(3)Mg(THF)(3)] (An = Th, 2; An = U, 3). Using a 2:1 reaction stoichiometry produces [Mg(2)Cl(3)(THF)(6)][(η(4)-Cb'''')An(η(3)-C(4)H(SiMe(3))(3)-κ-(CH(2)SiMe(2))(Cl)] (An = Th, [Mg(2)Cl(3)(THF)(6)][4]; An = U [Mg(2)Cl(3)(THF)(6)][5]), in which one Cb'''' ligand has undergone cyclometalation of a trimethylsilyl group, resulting in the formation of an An–C σ-bond, protonation of the four-membered ring, and an η(3)-allylic interaction with the actinide. Complex solution-phase dynamics are observed with multinuclear nuclear magnetic resonance spectroscopy for both sandwich complexes. A computational analysis of the reaction mechanism leading to the formation of 4 and 5 indicates that the cyclobutadienyl ligands undergo C–H activation across the actinide center.