951238-95-2Relevant articles and documents
Systematic studies of early actinide complexes: Uranium(IV) fluoroketimides
Schelter, Eric J.,Yang, Ping,Scott, Brian L.,Thompson,Martin, Richard L.,Hay, P. Jeffrey,Morris, David E.,Kiplinger, Jaqueline L.
, p. 7477 - 7488 (2008/10/09)
The reaction of (C5Me5)2U(CH 3)2 with 2 equiv of N≡C-ArF gives the fluorinated uranium(IV) bis(ketimide) complexes (C5Me 5)2U[-N=C(CH3)(ArF)]2 [where ArF = 2-F-C6H4 (4), 3-F-C 6H4 (5), 4-F-C6H4 (6), 2,6-F 2-C6H3 (7), 3,5-F2-C 6H3 (8), 2,4,6-F3-C6H2 (9), 3,4,5-F3-C6H2 (10), and C 6F5 (11)]. These have been characterized by single-crystal X-ray diffraction, 1H and 19F NMR, cyclic voltammetry, UV-visible-near-IR absorption spectroscopy, and variable-temperature magnetic susceptibility. Density functional theory (DFT) results are reported for complexes 6 and 11 for comparison with experimental data. The most significant structural perturbation imparted by the F substitution in these complexes is a rotation of the fluorinated aryl (ArF) group out of the plane defined by the N=C(CMe)(Cipso) fragment in complexes 7, 9, and 11 when the ArF group possesses two ofluorine atoms. Excellent agreement is obtained between the DFT-calculated and experimental crystal structures for 11, which displays the distortion, as well as for 6, which does not. In 7, 9, and 11, the out-of-plane rotation results in large angles (φ - 53.7-89.4°) between the planes formed by ketimide atoms N=C(C Me)(Cipso) and the ketimide aryl groups. Complexes 6 and 10 do not contain o-fluorine atoms and display interplanar angles in the range of φ = 7-26.8°. Complex 4 with a single o-fluorine substituent has intermediate values of φ = 20.4 and 49.5°. The distortions in 7,9, and 11 result from an unfavorable steric interaction between one of the two o-fluorine atoms and the methyl group [-N=C(CH3)] on the ketimide ligand. All complexes exhibit UV/UIV and U IV/UIII redox couples, although the distortion in 7, 9, and 11 appears to be a factor in rendering the UIV/UIII couple irreversible. The potential separation between these couples remains constant at 2.15 ± 0.03 V. The electronic spectra are dominated by unusually intense f-f transitions in the near-IR that retain nearly identical band energies but vary in intensity as a function of the fluorinated ketimide ligand, and visible and near-UV bands assigned to metal (5f)-to-ligand (π*) charge-transfer and interconfiguration (5f2 → 5f1-6d1) transitions, respectively. Variable-temperature magnetic susceptibility data for these complexes indicate a temperature- independent paramagnetism (TIP) below ～50 K that results from admixing of low-lying crystal-field excited states derived from the symmetry-split 3H4 5f2 manifold into the ground state. The magnitude of the TIP is smaller for the complexes possessing two o-fluorine atoms (7, 9, and 11), indicating that the energy separation between ground and TIP-admixed excited states is larger as a consequence of the greater basicity of these ligands.
