Preparation, Solution Behavior, and Solid-State Structures of (1,3-R₂C₅H₃)₂UX₂, Where R Is CMe₃or SiMe₃and X Is a One-Electron Ligand

Abstract

High-yield preparations of the uranium metallocenes [1,3-(Me3Si)2C5H3]2UCl2 (Cp‘ ‘2UCl2) and [1,3-(Me3C)2C5H3]2UCl2 (Cp⧧ 2UCl2) have been developed from the reaction of UCl4 and the corresponding magnesocenes Cp‘ ‘2Mg and Cp⧧ 2Mg in diethyl ether. The chloride ligands can be exchanged with either Me3SiBr or Me3SiI to give the uranium metallocene bromides or iodides. The fluorides were prepared by the reaction of BF3·OEt2 with Cp‘ ‘2U(NMe)2, Cp⧧ 2U(OMe)2, or Cp⧧ 2UMe2. The crystal structures of Cp‘ ‘2UCl2, Cp⧧ 2UCl2, Cp‘ ‘2UMe2, Cp⧧ 2UF2, and dimeric (Cp‘ ‘2UF2)2 are reported. The idealized symmetry of the monomers Cp‘ ‘2UX2 and Cp⧧ 2UCl2 is C 2 v when X is F, Cl, or Br and C 2 when X is I or Me; in the dimer, the idealized symmetry is C i . This preference is rationalized by intramolecular and intermolecular steric effects. The solution ring conformations and intramolecular exchange processes have been studied by variable-temperature 1H NMR spectroscopy. In all cases, the low-temperature limiting spectra are consistent with the idealized symmetry observed in the solid state.

Expanding the Chemistry of Actinide Metallocene Bromides. Synthesis, Properties and Molecular Structures of the Tetravalent and Trivalent Uranium Bromide Complexes: (C5Me4R)2UBr2, (C5Me4R)2U(O-2,6-iPr2C6H3)(Br), and [K(THF)][(C5Me4R)2UBr2] (R = Me, Et)

“…The compounds (C5Me4R)2UBr2 (R = Me (33), Et (34)) were obtained by treating (C5Me4R)2UCl2 (R = Me (31), Et (32)) with excess Me3SiBr (Scheme 1) similar to the method reported by Andersen for the preparation of the bent cyclopentadienyl species (1,3-R′2C5H3)2UBr2 [4] and (1,2,4-R′3C5H2)2UBr2 [5] (R′ = t Bu, SiMe3). Complexes 33 and 34 can be obtained in 96% and 90% yield, respectively, using this procedure, but it is important to add fresh Me3SiBr three times to the reaction mixture and to let the mixture react for at least 12 h each time.…”

“…The bis(cyclopentadienyl) complexes of uranium (C 5 Me 4 R) 2 UX 2 (R = Me or Et; X = Cl or I) [1][2][3], (1,3-R 1 2 C 5 H 3 ) 2 UX 2 and (1,2,4-R 1 3 C 5 H 3 ) 2 UX 2 (R 1 = t Bu, SiMe 3 ; X = Cl, I) [4][5][6][7] have been known for years, owing to the ease of preparation of reliable chloride and iodide starting materials. With the vast amount of literature attention devoted to (C 5 Me 4 R)UX 2 compounds, it is curious that the corresponding bis(cyclopentadienyl) uranium bromide systems have not been investigated to a similar extent.…”

“…An alternative method that has been employed to prepare uranium(IV) bromide complexes is halide exchange. For example, (1,2,4-t Bu 3 C 5 H 2 ) 2 UBr 2 (16) [5] and (1,3-R 2 C 5 H 3 ) 2 UBr 2 (R = SiMe 3 (17), t Bu (18)) [4] were prepared by reacting the chloride analogues with excess Me 3 SiBr, and (17) from its chloride analogue and BBr 3 [7].…”

“…The η 2 -suldenamido derivative (C 5 Me 5 ) 2 U(η 2 -t BuNSPh)(Br) (23) was obtained after long reaction times of chloride complex with MeMgBr [21]. Finally, protonolysis of (η 3 -C 3 H 5 ) 4 U with HBr provided (η 3 -C 3 H 5 ) 3 UBr (24) [22].…”

“…An alternative method that has been employed to prepare uranium(IV) bromide complexes is halide exchange. For example, (1,2,4-t Bu3C5H2)2UBr2 (16) [5] and (1,3-R2C5H3)2UBr2 (R = SiMe3 (17), t Bu (18)) [4] were prepared by reacting the chloride analogues with excess Me3SiBr, and (17) from its chloride analogue and BBr3 [7]. In recent years, oxidation chemistry has been developed to access a variety of uranium(IV) bromide complexes such as (C5Me5)2U(X)(Br) (X = N(SiMe3)2 (19) [17], ( i PrN)2C(Me) (20) [18], MeNC(Me)NAd (21) [19]), which were synthesized by treating (C5Me5)2U(X) with CuBr or AgBr.…”