The addition of 1 equiv of HSiPh(3) to UO(2)((Ar)acnac)(2) ((Ar)acnac = ArNC(Ph)CHC(Ph)O; Ar = 3,5-(t)Bu(2)C(6)H(3)), in the presence of 1 equiv of B(C(6)F(5))(3), results in the formation of U(OSiPh(3))(OB{C(6)F(5)}(3))((Ar)acnac)(2) (1), via silylation of an oxo ligand and reduction of the uranium center. The addition of 1 equiv of Cp(2)Co to 1 results in a reduction to uranium(IV) and the formation of [Cp(2)Co][U(OSiPh(3))(OB{C(6)F(5)}(3))((Ar)acnac)(2)] (2) in 78% yield. Complexes 1 and 2 have been characterized by X-ray crystallography, while the solution-phase redox properties of 1 have been measured with cyclic voltammetry.

In actinide chemistry, it has been shown that equatorial ligands bound to the metal centers of actinyl ions have a strong influence on the chemistry and therefore the electronic structure of the O═An═O moiety. While this influence has received a significant amount of attention, considerably less research has been done to investigate how the identity of the actinide metal itself (U, Np, Pu, Am) affects the actinyl stretching frequencies. Herein, we present the structural and spectroscopic characterization of six actinyl tetrachloride compounds (M2AnO2Cl4: M = Rb, Cs, Me4N; An = U, Pu) as well as the stretching and interactive force constants of the actinyl moiety in each species. Our results show a decrease in the stretching force constant and a weakening of the An═O bond when traversing the actinides from uranyl to plutonyl, which is interesting because the solid state molecular structures show a slight contraction of the An═O bond length when uranium is replaced with plutonium. Additionally, the interaction force constants for both the uranyl and plutonyl compounds were found to be negative, which corresponds to a reduction of the force constant for the symmetric stretching mode.

Addition of 2 equiv of B(C(6)F(5))(3) to [Cp*(2)Co][U(V)O(2)((Ar)acnac)(2)] (1) [(Ar)acnac = ArNC(Ph)CHC(Ph)O; Ar = 3,5-(t)Bu(2)C(6)H(3)] results in the formation of [Cp*(2)Co][U(V){OB(C(6)F(5))(3)}(2)((Ar)acnac)(2)] (2) in good yield. Reduction of 2 with 1 equiv of Cp*(2)Co generates [Cp*(2)Co](2)[U(IV){OB(C(6)F(5))(3)}(2)((Ar)acnac)(2)] (3), also in good yield. This reaction is chemically reversible, as shown by the reaction of 3 with AgOTf, which regenerates 2. Interestingly, addition of only 1 equiv of B(C(6)F(5))(3) to 1 does not produce the monofunctionalized U(V) complex. Instead, the products of disproportionation, namely, 3 and U(VI)O(2)((Ar)acnac)(2), are observed in a 1:1 ratio.

We present the structural and spectroscopic characterization of six uranyl tetrachloride compounds along with a quantified analysis showing the influence of both the crystallographic phase and the lattice solvent upon the vibrational properties of the uranyl moiety. From the uranyl symmetric and asymmetric stretching frequencies we use a valence bond potential model to calculate the stretching and interaction force constants of the uranyl moiety in each compound. Quantifying these second-sphere influences provides insight into the vibrational properties, and indirectly the electronic structure, of the uranyl ion in its ground state. These data provide a better guide for assessing the validity of future comparisons with respect to bond strength, length, and electronic properties among series of actinyl compounds where non-actinide variables may be at play.

A series of tetravalent An(IV) complexes with a bis-phenyl β-ketoiminate N,O donor ligand has been synthesized with the aim of identifying bonding trends and changes across the actinide series. The neutral molecules are homoleptic with the formula An((Ar)acnac)(4) (An = Th (1), U (2), Np (3), Pu (4); (Ar)acnac = ArNC(Ph)CHC(Ph)O; Ar = 3,5-(t)Bu(2)C(6)H(3)) and were synthesized through salt metathesis reactions with actinide chloride precursors. NMR and electronic absorption spectroscopy confirm the purity of all four new compounds and demonstrate stability in both solution and the solid state. The Th, U, and Pu complexes were structurally elucidated by single-crystal X-ray diffraction and shown to be isostructural in space group C2/c. Analysis of the bond lengths reveals shortening of the An-O and An-N distances arising from the actinide contraction upon moving from 1 to 2. The shortening is more pronounced upon moving from 2 to 4, and the steric constraints of the tetrakis complexes appear to prevent the enhanced U-O versus Pu-O orbital interactions previously observed in the comparison of UI(2)((Ar)acnac)(2) and PuI(2)((Ar)acnac)(2) bis-complexes. Computational analysis of models for 1, 2, and 4 (1a, 2a, and 4a, respectively) concludes that both the An-O and the An-N bonds are predominantly ionic for all three molecules, with the An-O bonds being slightly more covalent. Molecular orbital energy level diagrams indicate the largest 5f-ligand orbital mixing for 4a (Pu), but spatial overlap considerations do not lead to the conclusion that this implies significantly greater covalency in the Pu-ligand bonding. QTAIM bond critical point data suggest that both U-O/U-N and Pu-O/Pu-N are marginally more covalent than the Th analogues.