An Allyl Uranium(IV) Sandwich Complex: Are ϕ Bonding Interactions Possible?

Alkyl Coordination in meso-(ONO)2- Supported Uranium(IV) Complexes

A series of U(IV) complexes bearing alkyl and chloride ligands in the trans configuration was synthesized and characterized. Starting with the diastereopure U(IV) trans-dichloride complex meso-( tBu2PONO)UCl2(dtbpy) (1, tBu2PONO = 2,6-bis((di-tert-butylphosphino)methanolato)pyridine), four distinct alkyl groups were employed to prepare ( tBu2PONO)U(R)Cl(dtbpy), where R = (trimethylsilyl)methyl (neosilyl), 2a, R = 2,2-dimethyl propyl (neopentyl), 2b, and R = 2-methyl-2-phenyl propyl (neophyl), 2c. Alkylation occurs with specificity but generates a predominant species and a minor species corresponding to anti/syn regioisomers relative to the tBu2P groups of the ligand. For synthesis using R = methyl, the dimethyl complex ( tBu2PONO)U(Me)2(dtbpy), 2d, was prepared; the addition of 1 equiv of MeLi produced a mixture of products. Complexes 2a-2d were characterized using single crystal X-ray diffraction (SC-XRD), UV-vis-nIR, and 1H and 31P NMR spectroscopies.

Synthesis and comparison of iso-structural f-block metal complexes (Ce, U, Np, Pu) featuring η6-arene interactions

Reaction of the terphenyl bis(anilide) ligand [{K(DME)₂}₂L^Ar] (L^Ar = {C₆H₄[(2,6-ⁱPr²C₆H₃)NC₆H₄]₂}^2-) with trivalent chloride "MCl₃" salts (M = Ce, U, Np) yields two distinct products; neutral L^ArM(Cl)(THF) (1^M) (M = Np, Ce), and the "-ate" complexes [K(DME)₂][(L^Ar)Np(Cl)₂] (2^Np) or ([L^ArM(Cl)₂(μ-K(X)₂)])_∞ (2^Ce, 2^U) (M = Ce, U) (X = DME or Et₂O) (2^M). Alternatively, analogous reactions with the iodide [MI₃(THF)₄] salts provide access to the neutral compounds L^ArM(I)(THF) (3^M) (M = Ce, U, Np, Pu). All complexes exhibit close arene contacts suggestive of η⁶-interactions with the central arene ring of the terphenyl backbone, with 3^M comprising the first structurally characterized Pu η⁶-arene moiety. Notably, the metal-arene bond metrics diverge from the predicted trends of metal-carbon interactions based on ionic radii, with the uranium complexes exhibiting the shortest M-C_centroid distance in all cases. Overall, the data presents a systematic study of f-element M-η⁶-arene complexes across the early actinides U, Np, Pu, and comparison to cerium congeners.

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

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 [(η⁴-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 AnCl₄ proceed with intact transfer of Cb'''' to give the half-sandwich complexes [(η⁴-Cb'''')AnCl(μ-Cl)₃Mg(THF)₃] (An = Th, 2; An = U, 3). Using a 2:1 reaction stoichiometry produces [Mg₂Cl₃(THF)₆][(η⁴-Cb'''')An(η³-C₄H(SiMe₃)₃-κ-(CH₂SiMe₂)(Cl)] (An = Th, [Mg₂Cl₃(THF)₆][4]; An = U [Mg₂Cl₃(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 η³-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.