Organometallic Uranium(V)−Imido Halide Complexes: From Synthesis to Electronic Structure and Bonding

Abstract

Reaction of (C5Me5)2U(=N-2,4,6-(t)Bu3-C6H2) or (C5Me5)2U(=N-2,6-(i)Pr2-C6H3)(THF) with 5 equiv of CuX(n) (n = 1, X = Cl, Br, I; n = 2, X = F) affords the corresponding uranium(V)-imido halide complexes, (C5Me5)2U(=N-Ar)(X) (where Ar = 2,4,6-(t)Bu3-C6H2 and X = F (3), Cl (4), Br (5), I (6); Ar = 2,6-(i)Pr2-C6H3 and X = F (7), Cl (8), Br (9), I (10)), in good isolated yields of 75-89%. These compounds have been characterized by a combination of single-crystal X-ray diffraction, (1)H NMR spectroscopy, elemental analysis, mass spectrometry, cyclic voltammetry, UV-visible-NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. The uranium L(III)-edge X-ray absorption spectrum of (C5Me5)2U(=N-2,4,6-(t)Bu3-C6H2)(Cl) (4) was analyzed to obtain structural information, and the U=N imido (1.97(1) A), U-Cl (2.60(2) A), and U-C5Me5 (2.84(1) A) distances were consistent with those observed for compounds 3, 5, 6, 8-10, which were all characterized by single-crystal X-ray diffraction studies. All (C5Me5)2U(=N-Ar)(X) complexes exhibit U(V)/U(IV) and U(VI)/U(V) redox couples by voltammetry, with the potential separation between these metal-based couples remaining essentially constant at approximately 1.50 V. The electronic spectra are comprised of pi-->pi* and pi-->nb(5f) transitions involving electrons in the metal-imido bond, and metal-centered f-f bands illustrative of spin-orbit and crystal-field influences on the 5f(1) valence electron configuration. Two distinct sets of bands are attributed to transitions derived from this 5f(1) configuration, and the intensities in these bands increase dramatically over those found in spectra of classical 5f(1) actinide coordination complexes. Temperature-dependent magnetic susceptibilities are reported for all complexes with mu(eff) values ranging from 2.22 to 2.53 mu(B). The onset of quenching of orbital angular momentum by ligand fields is observed to occur at approximately 40 K in all cases. Density functional theory results for the model complexes (C5Me5)2U(=N-C6H5)(F) (11) and (C5Me5)2U(=N-C6H5)(I) (12) show good agreement with experimental structural and electrochemical data and provide a basis for assignment of spectroscopic bands. The bonding analysis describes multiple bonding between the uranium metal center and imido nitrogen which is comprised of one sigma and two pi interactions with variable participation of 5f and 6d orbitals from the uranium center.

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)

“…Comparison of the methyl proton resonance of C 5 Me 5 by 1 H NMR spectroscopy reveals an upfield shift in the order I (9.85 ppm) < Br (8.76 ppm) < Cl (7.85 ppm) << F (3.19 ppm). This trend has been observed before in other cyclopentadienyl complexes and it is directly correlated with the π-donating ability of the halide ligand [51]. Similarly, comparison of the methyl peaks of the C 5 Me 4 Et ligand of 36 (11.9, 8.5, 7.8, 7.8 and 6.6 ppm) and 38 (11.9, 9.11, 9.07, 8.3 and 7.8 ppm) shows the same pattern, where the peak positions of (C 5 Me 4 Et) 2 U(O-2,6-i Pr 2 C 6 H 3 )(Br) appear downfield from those of (C 5 Me 4 Et) 2 U(O-2,6-i Pr 2 C 6 H 3 )(Cl).…”

Pentavalent uranium chemistry—synthetic pursuit of a rare oxidation state

“…Bonding analysis using DFT on the model complexes (CsMes)2 U(=N-Ph)(F) ( 1 28) and (CsMeshU(=N-Ph)(I) (129) supports these findings and describes the multiple bonding between the uranium metal center and imido nitrogen as consisting of one a-and two 1t-interactions with variable 50 participation of 5f and 6d orbitals from the uranium center. 90 The X /Y ligand did not significantly influence the imido parameters. However, as expected on the basis of the ionic radius of the XIY atom S6 the U-X/Y bond length decreases down the series, with U-F < U-Nsp2 < U-Nsp3 < U-CI < U-S < 55 U-Br < U-S e < U-I < U-Te.…”

“…Andersen and co-workers reported the oxidation of (CsH4Me)3U(THF) (89) Complex 90 was characterized structurally (Figure 22). The most notable geometric parameters are the short U=N Figure 22 Ball-and-stick representation of (C 5 H. Meh U(=N-Ph) (90).…”

A relativistic DFT study of magnetic exchange coupling in ketimide bimetallic uranium(IV) complexes

“…Such coordination in the diuranium(IV) complex, throughout the ketimide (1,4-phenylenediketimide) bridging ligand, which appears also in bis(imido) diuranium(V) species [63,90], is likely to maximize the possibility of electronic and magnetic communication between the two metallic centres. Different authors [106,115,120] attributed this peculiar linear U-N-C coordination, to a significant participation of the uranium 5f orbitals in metal-N bonding. This U-N(ketimide) coordination exhibits both r and p interactions between the central metal and bis(ketimide) bridging ligand via the nitrogen electron pairs.…”